DOCUMENT RE UME

ED 054 927 SE 011 306AUTHOR Kaben, Jerrold WilliamTITLE How Far a Star. A Supplement in Space Oriented

Concepts for Science and Mathematics Curricula forIntermediate Grades.

INSTITUTION National Aeronautics and Space Administration,Washington, D.C.

SPONS AGENCY Office of Education (DHEW), Washington, D.C.PUB DATE 69NOTE 112p.

EDRS PRICEDESCRIPTORS

ABSTRACT

MF-$0.65 HC-$6.58*Aerospace Technology; *Astronomy; InstructionalMaterials; 4-Intermediate Grades; *Mathematics;Measurement; Resource Materials; *Science Activities;Scientific Principles

Space science-oriented concepts and suggestedactivities are presented for intermediate grade teachers of scienceand mathematics in a book designed toltelp bring applications ofspace-oriented mathematics into the classroom. Concepts andactivities are considered in these areas: methods of keeping time(historically); measurement as related to time, distance, andastronomy, including lunar photographs and measurement activities;communication in space, sound, and satellites; measuring theatmosphere; and measuring and interpreting the light from stars. Aglossary of space terms, an aerospace bibliography, and a subjectindex are included. (PR)

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HOW FAR A STAR

A SUPPLEMENT IN SPACE ORIENTED CONCEPTS

FOR SCIENCE AND MATHEMATICS CURRICULA FOR INTERMEDIATE GRADES

Prepared fr9m materials furnished by the NationalAeronautics and Space Administration in cooperationwith. the Unitfi: States Office of Education by aCommittee on Space Science Oriented Mathematics

1969

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CONTgNTS

Chapter ITHE MYSTERY OF TIME 1

History of Time, Early Timekeepers, Sundial Model, Mechanical Time-keeperi, The Foucault Pendulum, Time in Space, Review of Scientific

Notation, Rendezvous in Space

Chapter IIMEASURING THE UNKNOWN -

17

Time Standards, Need for Better TimekeeDers, Units of Time, Limitsand Errors, Earth as a Timekeeper, Rotation and Revolution, Sideraland Solar Days, The Moon, Phases and gotions, Measuring with theVernier ahd Ruler, Distances in Space, Errors in Measurement, SatelliteOrbits, Ranger Photographs, Moon MeaSurernents with Scale, MoonAtlas, Measurement Techniques

Chapter III"EMPTY" SPACE

67

Discussion of Space, Communication in Space, Sound, Satellite Com-munication, Weather Satellites, Weather over Earth

Chapter IVTHE MEASURE OF OUR ATMOSIIFIERE

79

History, Atmospheric Levels, Nature of Cases, Weather Observations,VoEume, Density, and Pressure, Measurenient of the Upper Atmos-phere, Density, Temperature, Instruments of 'Measurement

Chapter VWHAT LIGHT CAN TELL US -

97

Measurement, Direct and Indirect, Stars, Brightness and Magnitude,Celestial Coordinates, Spectra of Light, Wavelength, Identification ofSpectra, Model Spectroscope and Its A iicatior

Chap rer ViTO THE FUTURE

109

People and the Space Program

GLOSSARYr, 111

BIBLIOGRAPHY121

INDEX. . . . . ..... .... .123

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You can usually judge the length of aninch with reasonable accuracy. But onehour of time may seem much longer thananother. Have you heard the saying, "Thereis nothing more plentiful than time?"Certainly this is true when you are waitingeagerly for something pleasant to happen.But when you are enjoying yourself at aparty, you would be more likely to agreewith another proverb, "Time flies. '

So we need a way of measuring timethat is the same for play-time, work-timeof just plain "waiting" time. Write whatYou know to be our basic methods of timemeasurement. Did you ineude stopwatches, rotation of Earth, the atomicclock, and star transits?

;Early measurement methods were in-exact. As our lives become more complex,we need to measure time more accurately.But an exact measure is still one of themost perplexing problems of our space ageand the search for an exact standard of timemeasurement continues.

Early Americans recorded the durationof time in such units as moons and winters.Is it possible to imagine a NASA/GoddardSpace Flight Center scientist saying an OGO(Orbiting Geophysical Observatory) satel-lite has been in orbit for "five moons?"Obviously, the units of moons and winte.rsare not very useful today. However, they doraise a question common to all units ofmeasurement where does the measure be-gin and where does it end? Whatever unitof measure we use should give the measureof time meaning. It needs to help us tounderstand the duration between "before"and "after."

Early man, like today's space scientists,needed to know enough about the passageof time to make predictions so that he couldgive order to his life. Copy and completeFigure 1-4 to list ways early man used timefor prediction. Make a similar list formodern man. You can see that we nowneed a more accurate measurement of timethan in the past.

Beginning about 4000 B.C. the civiliza-tions of Babylonia and Egypt flourishedin the valleys of the Tigris, Euphrates, andNile Rivers. Did you know that thesenations are credited with the invention ofcalendars as well as the sciences of astron-omy and mathematics?

4

SOME APPLICATIONS OF TIME PREDICTIONS

EARLY MAN MODERN MAN

crop planting

flock movement

the first frost

river floods

food animal migrations

solar flares

launch windows

satellite orbits

Figure 1-4

Read the history of Central Americaand find another people who made veryaccurate predictions by using unusual meth-ods (Fig. 1-5).

To the Babylonians we credit thoseparts of our measuring system based ontheir mystic number twelve. Perhaps thiswas because astronomers observed thatthere seemed to be twelve full moons inthe course of a year. Can you list thoseparts .of our present measurement systemswhich involve twelve as a factor? Forexample, the Babylonian circle had 360dexees (12 x 30). There are 24 hours in aday (12 x 2), 60 minutes in an hour (12 x5), 360 days in a year (12 x 30).

As one of the first observations made byman was that the seasons reoccured after aperiod -of about twelve moons, the measureof a year was considered to be abouttwelve moons. Each moon was namedin relationship to some event in the lifeof plants and animals or some sacredobservance. Each month began at sundownof the day when the new crescent moonwas seen in the sky.

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a result, hmar calendars (Figure I-6), neededan extra month every few years in order tomatch the seasons and make time predic-tions more exact.Certain lunar measured calendars have

been -retained for use today_ The calendarused in some sections of India, the Hebrewreligious calendar, and the Christian methodfor fixing the date of Easter emplo-csphases of the moon as a means of nieasuringtiine. Probably no one in all Babylonia,Egypt, Greece or Rome had ever thought ofa clock, yet these people could measurethe passage of time, appropriate to the needsof their culture.

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When man first tried to tell time byobserving the movement of our planet,Earth, it was as difficult as it would befor you to tell time from a clok which hadneither hands nor face_ Lost, forever in theyears be-fore history was written, are theworks of the early men who watched themoving shadows cast by the sun, and usedthem to mark the passage of time, (FigureI-7 ) Let's examine- how you can makemeaSurements similar to those of the "lost"'scientists.From sunrise to sunset, mark the end ofa shadow cast by a utility pole, flag pole,fence post or other vertical, staff. Record

and position of the shadow at various timesduring the day. Keep a record for t.IT, schoolyear then you can compare the positionsand lengths of the shadows at the beginningof the school year, during the winter, dur-ing the spring and at the end of the schoolyear.

To help you understand the differentshadow lengths, conduct the followinginvestigation. Place an unshaded lamp, toserve as a sun, in the center of a darkenedroom. Attach a small stick or a figuremade of pipe cleaners to a world globe.Place the globe about 2 or 3 meters fromthe "sun" so that its axis is tilted 231/2degrees toward the "sun." Measure theshadow cast by the stick. Move the globeto the other side of the unshaded bulb,placing it exactly the same distance fromthe lamp as it was before. Do not changethe tilt of the axis. It will now tilt awayfrom the "sun." Measure the shadow'slength. Was the shadow longer when theaxis was tilted toward or away from the

Figuie 1-7

the length for every hour as in Figure 1-8.What means can you devise to accurately:determine the end of the shadow; measurethe time intervals; and mark shadowlengths? What , kinds of tables, graphs,scale drawings, etc., can you develop tokeep a record of your results?

You can investigaie the way time canbe determined by the sun s rays and howthe tilt of Earth's axis causes sunlight tostrike Earth at different angles. Using themethods developed for Figure 1-8, recordshadows cast over a long period of time.If possible, mark the shadow's positiondirectly on the surface of the playground,your driveway or other permanent location.If not, record them on a large piece of chartpaper or wrapping paper. Again note theexact location of the pole's shadows at thesame time each day and record the length

sun? You can see that the actual shadowlength will vary according to the objectyou placed on the globe. Remember the

place on Earth which is receiving the mostdirect rays will have the shortest shadows.What would you hypothesize if you movedthe globe (tilted the same amount and inthe same direction) to other positionsequidistant from the sun?

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Winter -9 1/2 hoursof daylight

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Summer - 15 hours of daylight

Autumn - 12 hoursof daylight

Winter-9 1/2 hoursof daylight

Figure 1-9

You also know from daily observationsthat the number of hours of daylight variesthroughout the year. Figure 1-9 illustrateshow the hours of daylight and darknessvary at the NASA/Goddard Space FlightCenter, Greenbelt, Maryland, U.S.A.

If we recognize that the changes in yourshadows and the apparent position of thesun are due to the motion of Earth in space,we must notice that there are two distinctmajor motions. The first you have justinvestigated: the movement of Earth in itsorbit around the sun, revolution. Thesecond motion, of course, is the rotationof Earth on its axis (Figure I-10).

Earth makes a complete rotation on itsaxis in about 23 hours and 56 minutes. Wecall this a sidereal or star day. Our solarday, however, is a few minutes longer thanthis because as Earth rotates it continues torevolve around the sun, (Figure I-11). Dueto variations in orbital speed our solar day

Figure I-11

varies from 23 hours 59 minutes to a littleover twenty four hours.

If we seek to det0-mine how far the sunwill appear to move in the sky in one hour,we calculate that if Earth rotates a completecircle of 360° in twenty four hours, thenumber of angular degrees for each hour ofrotation equals 360/24 or 15° per hour. Thesun then will appear to move 15° per hour.

If we select the point where the sun isshining directly on Earth as solar noon, wecan tell the time at vari,3us points aroundthe globe by moving 150 In either direction(Figure 1-12).

CDFigure 1-13

Figure 1-12

These hour lines are the meridian& ThePrime Mericfian which passes through Green-wich, England, serves as a starting point formeasurement east and west around theglobe. (Figure I-13.)

To summarize, Earth rotates from westto east. Therefore, the sun's apparentpath is from east to west and your shadowrecords move from west to east. The sun'sapparent motion across the sky can be usedto measure time.

Figure 1-14

Prior to 2000 B.C., the first knownshadow clock (Figure 1-14) was built Thisgave a measure to parts of the day.

A stick was joined to a long, narrowpiece of wood to form a T (Figure 15).The piece of wood had markings whichrepresented hours of the day. This tookup a lot of space and was later replacedby the sundial which was both more con-venient and more accurate,

Based on observations that the lengthof the shadow changed with the seasons,the sundial was developed to Peatlit allow-ances for position on Earth and the seasonsof the year. You have seen, how yourown shadow charts could be used to tell

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time. But a major difficulty would be tomake charts that would be correct regard-less of the season or your position on Earth.

You can build a measurement instrumentthat will record local sun time correctedfor position and season. Your sundial willhave four parts (Figure 1-16). The shadowstick or gnomon (pronounced nö'man), theequatorial ring on which to read gnomonshadows, the equatorial ring support, andthe base are the four parts of the sundial.Use stiff cardboard or flexible metal forconstruction of the gnomon, the equatorialring, and support. If cardboard is used, aweather-resistant spray will rna,ke your

EQUATORIAL RING1/2IN.

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Figure 116 Figure 117

sundial more permanent. The base is madeof wood.

Note, when constructing the gnomon,the angle 0 (called "theta") should beequal to your local latitude. Your localiatitude may be determined from a map.Measure this angle carefully with a pro-tractor. In Figure 1-16, the distance AB isgiven for a latitude of 40°. If your latitudeis less than 40°, angle 0 will be ' 's than40°. If your latitude is greaterangle 8 will be greater than 40°.

After making the parts according 1..0 Ithedimensions in Figure 1-16, bend the cequa-torial ring into a circle with the madcf3ngson the inside, and fasten the two inchlap with glue. Slide the gnomon into thenotch of the wooden base and insert -theequatorial ring support into the gnomon..After the equatorial ring slits are hookedon the supports, your sundial should It>oklike Figure I-17.

In use, your sundial should be on a love',surface with the gnomon pointing due-North. North may be determined at niaktfrom the position of the North Sttar,Polaris, or in the daytime by using acompass. On sunny days, the time is readfrom the position of the leading edge of thegnomon shadow on the equatorial ringscale. This will be your local solar time.

Civilizations using sundials sought toovercome difficulties such as cloudy daysand darkness by the use of devices that didnot depend on Earth's rotation. Two suchdevices were water clocks and hour glasses.Both inventions were based on the principleof rate of flow.

About 800 or 900 B.C. the water clock,a clepsydra (klep' se-dre), was developed.It was a bowl- with a small hole in thebottom. When the bowl was filled, thewater dripped out slowly. By marking theinside of the bowl with lines, time wasmeasured as the water level became lower.

The trouble with the clepsydra (whichmeans water thief) was that someone hadto fill the bowl as soon as the water ranout. Then too, the rate of water flowchanged as the reservoir emptied and, ofcousse, a frozen water clack was not a goodmersuring device!

Aas the art of glass blowing progressedduriag the 8th Century A.D., the sandglass or hour glass was invented. Usingsandi-instead of water, the grains emptiedout of one glass vessel through a hole intoanotner glass vessel of the same size. Thesanz glass proved best for measuring shortpeninds of time. A three-minute glass, forinst=ce, may be used in your home totime boiling eggs or telephone calls. Butyou would need many many sand glassesto measure a whole day in hours, minutes,and seconds. And someone would have tobe there to turn the glass over when thetop vessel is empty.

Figure 1-19

Throughout the evolution of bettertime keeping, more accurate mechanicaldevices have been sought. All mechanicalclocks have several things in common:hands, dials, bells or other ways to markthe passing of time; the escapement orregulation devices; and a source of power.We often think of the pendulum in thisconnection.

Figure 1-20

When he was only nineteen, Galileo isreported to have used his pulse as a meansto measure time for the comparison of theswing times of a pendulum. A more de-tailed, account of Galileo's experiment isgiven-lin another book in this series, FromHere, Where? pp. 82 ff.

You can compare Galileo's measure-ments with experimental results of your.own by constructing a simple pendulum.

Tie a small Weight such as a bolt or leadsinker, to a string about 10 to 15 incheslong and let it hang down as you hold the,other end of the string. Now pull theweight, a pendulum bob, to one side :didrelease it (Figure I-21). It will ,beginswinging back and forth.

Cut the string in half and repeat yourobservations. What change do you observein the period of time measured for a corn-plete swing? The period will be shorter.The length of the string (t) arid the-Periodof the swing (T) are related. As the lengthof the string is changed the period of swing

varies. A simple relationship of L to T is asfollows:

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very cic.. _ to this relationship. They wouldbe exact, except that the usual experimentalerrors in timing swings, measuring length,and det rmining the end of the swing willincur lilt differences.

To ch--,Tck your observations, make atable of your results like Figure 1-22.Notice that you have two variables !.h. theconstructiten of your pendulum; the lengthof the pendulum, and the weight of the

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bob. As you use your pendulum, anothervariable is the size of the arc used to startthe pendulum swinging. We are interestedin measuring the time necessary for onecomplete swing of the pendulum._ _

Time five successive swings for thePerid-iihim lengths as in Figure 1-23. Meas-ure length from the pivot point to the.center of the bob. Use a complete swingcycle (back and forth) of the bob as theperiod. You will find that a support foryour pendulum, such as a thumbtack overa doorway or a ladder, will help your in-vestigation. From your measurement offive periods, find the average for oneperiod. For example, if you obtained fivecomplete swings in twelve seconds, theaverage period for one swing would be12/5 = 2.4 seconds.

At The top of the arc, gravitationalforce directs the pendulum bob towardthe center of Earth. The string acts as acontrol on the direction of fall. Inertia,according to Newton's first law of motion,carries the bob to the top of the other sideof the arc (Figure 1-23). There the bobreaches the point where Earth's grairitationalforces are gteater than inertial forces andthe bob swings back.

If no other forces acted on the pen-dulum, we would have perpetual motion.However, friction at the pivot and frictionbetween the moving pendulum parts and'air molecules result in the pendulum grad-ually slowing to a stop.

Figure 1-24 illustrates how these prine3-pies are applied to a mechanical clock.The pendulum regulates the motion andthe hang:no weight provides the energy toovercome the action of frictional forces.Yau may see a similar arrangement :;-.1

some "cuckoo" clocks. One of the cuckooweights is for the pendulum mechanism,the other is to operate the cuckoo.

Figure 1-23 shows how grairitationalforces cause the downward movement ofthe bob and inertial movement forces it-to the end of its arc. You know that theforce of gravity depends on many factors;altitude, the shape and density of Earth,and Earth's rotation. As a consequence, apendulum clock moved from one locationto another on Earth or in space would notkeep the same time. Therefore, most clockpendulums have a screw adjustment tocorrect for local variations.

The movement of our Earth on its axisin space also has another effect on themotion o-f pendulums. The French phys-icist Jean Bernard Leon Foucault usedthis motion to demonstrate that Earthrotates on its axis.

FOucault suspended a very long pendu-liim frOm the ceiling of a high room andSet the-pendulum in incition. Aftet obServ-ing the pendulum for many hours, hediscovered that the pendulum was notswinging in the same geographical directionas it was when it started. That is, if hispendulum was swinging back and forthtoward one wall of the room, it graduallywould appear to change its direction toward

PEN DULUM

Figure 1-24

Figure 1-25

the next wall and so on unt.11 the pendulumappedred to be swinging back in the direc-tion of its starting point.

By doing the following project you canexamine Foucault's reasoning that Earthand the observer are moving in relation tothe direction of swing of the pendulum.

You will need: a rotating mechanism(phonograph turntable, piano stool or lazySusan; .support. such as wood dowel; heavyweight, such as a lead sinker; string; squarewastebasket, ring stand or other support;and clamps (Figure 1-25). _

Tie the weight to one end of a stringabout 60 centimeters long. Attach the otherend to a Ph foot piece of dowel or broomhandle about 30 centimeters long. Placethe dowel across the top of a wastebasket,ring stand or other support, allowing theweight to swing freely. Place the supporton top of the lazy Susan or piano stooLSet the pendulum in motion and then ro-tate the lazy Susan or piano stool veryslowly.

See if the swing direction changes withrespect to the platform. As Earth movesunder the pendulum, the pendulum appearsto change the direction of its swing. Aswinging pendulum at the North Polewould appear to make a complete turn,360°, in 24 hours. As you move towardthe Equator, the effect becomes less pro-nounced and a longer and longer period isnecessary to make a 360° change. At apoint exactly perpendicular to the axis of

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Eatth, the Equator, tl, woud be noapparent change in dire- non sina:e at thispoint Earth is no longr "turninkg under"the pemduium.

What's up There?, a ither boOk in thisseries will provide- yor with some usefulinfor, aation on applican. ,ns of pendulumprinci'ples in satelllite in ruments. Readparticalarly the secthion or usirng -three pen-dulum accelerometfas tr: 2rovide measure-ment of satellite possition , pp. 61-67.

How would yoia descm'be the distancebetween two cities? Wm_i_ your answer inunits of miles or hours? If your responsewas in hours, yolu wouild be using thelanguage of astrommers. kstronomers usethe term light-year to imdkate tthe distanceto nearby stars. A light-rear is the distancelight would travel in one year at a rate ofabout 300,000 kilometer, per second.

Our closest star after :'he sun is ProximaCentauri. Proxima Centauhi is about 4.3light years away, or the arne distance thatlight will travel in 4.3 y -:-ts at the rate of300,000 kilometers per econd. How faraway is Proxima Centauri in kilometers? Tofind out, first calculate how far lighttravels in one year. To make this calcula-tion, you will need to multiply. 300,000by the number of seconds in one min-ute (60), the number of minutes in onehour (60), the number of hours in aday (24), the number of days in a year(36514), = (300,000) x (60) (60) (24)(36514), = (300,000) x (31,557,600) =9,467,280,000,000 = 9..46728 x 1012 kil-ometers._ A generally used value for the Iihtyear is 9.46 x 10" kilometers (read asnine and forty six hundredths times ten tothe twelfth power kilometers). Therefore,the distance to Proxima Centauri would be4.3 x 9.46 (10" ) = 40.678 x 10' . Inscientific notation, it is 40.67 (1012), andwould be read as "forty and sixty sevenhundredths times ten to the twelfth power."

rf you do'nof understand scien-tifiC-no-tation, copy and complete Figure 1-26.Then read pp. 4-5 and p. 80 in What'. -11There, the first book of this series.

In our space age, time is an importantfactor to us. When do you launch a spacevehicle so that it will get where you want itto go, and arrive when you, wanted it toget there? For example, suppose you

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Figure 1-26

planned to have your rocket rendezvous inspace with another spacecraft. Since arocket carries only a limited amount offuel and spends most of its time coasting inspace, you would have to leave Earth atjust the right time to arrive in positionalong side the vehicle with which you wish torendezvous. There would be no use arrivingin orbit on one side of Earth when therendezvous vehicle was on the other side.

Let's suppose you wish to rendezvousover a particular point in the AtlanticOcean. Assume that an Agena targetvehicle in orbit travels about 5 miles persecond and that it takes about 90 minutesfor Agena to orbit Earth. You can see thatif you wish to meet the Agena in orbit atone point over Earth's surface, you willhave that opportunity once every 90minutes. In addition, if you do not wantto miss Agena by more than 5 miles, yourtake-off will have to be accurate within onesecond. Every 90 minutes there will be aone second interval during which you mustlaunch to accomplish your rendezvous asplanned. That one second time interval iscalled a launch window.

Figure 1-27 shows events which are.pos-sible during different periods of time. Oneof the shortest periods we know is thelength of time it takes a proton to revolveonce in the nucleus of an atom. Thelargest period of time we know about isour estimate of the age of the universe.

As man has passed through time formany, many years on his journey tocivilization, he has learned that he livesin a world of many rhythms. He foundrhythms high in the sky, and buried deep inthe rocks. He found rhythms in the heartof the atom, and out in the far reaches ofspace. And, besides those that he foundin nature, he learned how to make many

TIMESCALE OF THE UNIVERSE

Durationsin seconds Ages or periods of time

1022 unknown outer limits of time

10" possible oge of the universe (?)age of the eorth (5 billion years)one revolution of the sun oround the galaxy

10'S oge of younger mountain systennduration of hurnon race (o million years)written history

1010 age of a nation0 year 0ne revolution of eorth around suna month

/OS o day one rotation of the earthan hour eating ale meola minute taking of a breath

a second a heartbeatblink of an eyeMILLI vibration period of audible sound

WS MICRO a flash of lightningdumtion of a muon particleNANO time far light to cross a room

le° vibration period of radarPICO time far on air molecule to spin oncevibration period oF infra-red radiation

10-1S vibration period of visible lightvibration period of x-rays

10-20 vibration period of gamma raystime far a proton to revolve once in the nucleus of an atom

lo-25 unknown inner limits of time

Figure 1-27

more. By mastering these rhythms he de-veloped the art of measuring thne So nowhe can measure time, not only for seconds,days, and years not only for centuriesbut for billions of years on the one hand,and a billionth of a second on the other.But his mastery of rhythm means morethan the measurement of time. It meansan increasing understanding of nature. Hisknowledge of rhythms not only lights upthe hidden, dark corners of the past, but italso helps him to plan for the future.Armed with knowledge of the rhythms ofthe universe, man continues to pass throughtime.

In the next chapter we will see whathas been done to standardize our time sothat we all can "be on timer'

_

r11

MEASURING THE UNKNOWN

In order to describe the measure of outerspace, we need to consider distance as itrelates to time. We can experience, or"feel," the measure of time and distance,used in our day to day living. We cannot"feel" the measure of outer space. So wemust use mathematical models to help usdescribe measures that are beyond oursenses, our "feelings."

Let's begin with some measurements weknow and can feel. Then use these to de-velop ways to describe the measure of thingswe may never feel and distances which wemay never travel.

Everyday we are using measurementswhich we know by feeling. Some are theresult of simple observations such as theheight of a step as we approach a stairway,the time of day when we are hungry orsleepy, or the speed of an approaching caras we cross the street. Simple proceduresfor measuring distance are estimating byeye, ear, or by using a rule or tape measure.Obviously we cannot use these to measurethe distance to an orbiting satellite or thespeed of Earth as it orbits the sun. Todaywe have to describe very large and verysmall measures such as one angstrom(0.00000001 (10-8) centimeters), the timeof one nanosecond (0.000000001 (10-9)seconds), or the speed of light (186,000miles per second).

Remember also that measurementsimply supplies information to help a sci-entist or you to answer a question orto solve a problem. Measurement is subjectto error. So we must develop preciseinstruments and use them carefully. Whatappears to be a correct answer may turnout to be incorrect if more precise measur-ing instruments and techniques are usedto collect the information.

Now let's attempt to make some meas-urements which we can "feel" to help us tounderstand the more precise instrumentsused by our space age scientists today.

Take your pulse: Count the pulsationsin a minute of time. What is your pulserate in pulses per minute? Have sortie ofyour friends take their pulse counts. Dopulse counts vary? Some of the factorsthat effect pulse counts include activity,rest, age, and emotion.

Most people have a pulse rate of about72 pulses per minute. We will use this as astandard for this exercise. Is your own ratehigher or lower than our selected standard?if 72 pulses occur in one minute, then theaverage number of standard pulses persecond is 72/60 or 1.2 pulses in one second.Twenty seconds of clock time would beequal to 20 x 1.2, or 24 pulses of "hearttime."

If we were to keep time in "standardheart time," we could develop a scale asfollows:

Clock Time Heart Time1 second 1.2 pulses1 minute 72.0 pulses

In space science, however, we need away to describe very long periods of timeand very short periods. Sometimes we areable to use smaller numbers by introducinglarger units. For example, instead of saying365 days, we describe this period of timeas one year. We also say one mile insteadof 5,280 feet. It is more convenient to usethe larger unit and the smaller number.

If we introduce larger units into standardheart time, we may describe 1,000 pulsesas 1 kilopulse. The word "kilo" comes tous from the Greek language and is trans-lated as "one thousand." We may sub-stitute 1 megapulse for 1,000 kilopulses,"mega" from the Greek meaning great.Summarizing we may saY:

1,000 pulses = 1 kilopulse1,000 kilopulses = 1 megapulse

Clock Time

1.0 second0.1 seconds0.01 seconds0.001 seconds or1 millisecond0.000001 seconds or1 microsecond0.000000001 seconds1 nanosecond0.000000000001 secondsor 1 picosecond

Read as:

one secondone tenthone hundredthone Jiousandth

one millionth

one billionth

one trillionth

Heart Time

1.2 pulses0.12 pulses0.012 pulses0.0012 pulses or1.2 millipulses0.0000012 pulses or1 micropulse0.0000000012 pulsesor 1.2 nanopulses0.0000000000012pulses or 1 picopulse

Table II- 1

How many pulses are in a megapulse?

1 rmgapulse = 1,000 kilopulses

1 megapulse 1000 x 1000 pulses

1 megapulse = 1,000,000 or I million pulses

Now we can add these to our table.

lthour 4,320.0 pulses or4.32 "kilopulses"

1 year 37,842 "megapulses"We could describe the five hour drive

from New York to Washington, D. C. instandard heart time, as taking 21,600pulses or 21 kilopulses, plus 600 .pulses.Mariner IV's trip to Mars took sevenmonths. Seven months equals 3 mega-pulses, plus 1 kilopulse, plus 104 pulses ofstandard heart time.

An exceptional high school sprinter canrun the 100 yard dash in 9.8' seconds.From Table II-1 we. standardized 1 secondas 1.2 pulses. So we are able to expressthis in "standard" heart time' as 100 yardsin 9.8 x 1.2, or 11.76 pulses. He is able toaverag6 1 yard per 11.76/100, or 0.1176pulses over the 100 yard distance. TheRanger IX's pictures of the moon wererecorded to the thousandth of a second(0.001 seconds). This would be equal to.12 ten-thousandths of a pulse, or 0.0012of a pulse.

Scientific Notation

1.2 pulses1.2 x 10-1 pulses1.2 x 10-2 pulses1.2 x 10-3 pulses

1.2 x 10-6 pulses

1.2 x 10-9 pulses

1.2 x 10-1 2 pulses

Converting our table to standard hearttime, we have:

1 millipulse= 10-3 pulses

0.001 millipulses = 1 micropulse= 10-6 pulses

0.001 micropulses 1 nanopulse= 10-9 pulses

0.001 nanopulses = 1 picopulse= 10-1 2 pulses

Our heart time is based on an imaginarystandard heart, . pulsating at a rate of 72pulses per minute. If we were to keeptime in standard heart time, our standardheart would be placed in the NationalBureau of Standards at Washington, D.C.It might be placed next to the standardmeter and standard kilogram (Figure 11-3).

0.001 pulses

Prior to the invention of our familiarmechanical and electrical clocks, the pulsewas used as one of man's timing methods.You know how Galileo discovered theprinciple of the pendulum by timing theswing of a cathedral chandelier with his

pulse beat. Huygens (Hi gens) used Galileo'sdiscovery of the principle of the pendulumto regulate the first mechanical clock.

Run in place for 15 seconds. Now takeyour pulse rate in pulses per minute. Com-pare this rate to your rate when you wereat rest.

Pulse rate at restPulse rate after running

Your heart speeds up and slows down.Our standard heart also would vary withchanges in conditions such as pressure,oxygen supply, temperature, food supply,and activity. Consider, for example, whatwould happen to our methods of measuringif the foot became longer or shorter, or ifthe pound became heavier or lighter. Al-though standard heart time is a possibilityand was useful in the past, it is obvious thatscientists have attempted to find othertimekeepers which show less vadation. Thefollowing exercises will help you understandanother historical timekeepMg method.

The answers for the exercises in thisChapter will be found at the end of thisChapter.Exercises:

1.a.

Figure 11-5

With a pin, punch a small hole in thebottom of a paper cup. Fill the cupwith water. Place the cup overanother cup, so that the water dripsinto the second cup. Suggestion:Make the hole large enough so thatyou have 50 to 80 drops per minute.Count the number of drops of waterin one minute of time. Record thedrops in a minute. Repeat, countingthe number of drops in a minute.Repeat the procedure three moretimes. Record your results in a tablelike the one below:Test 1 ? drops in 1 minuteTest 2 9 drops in I minuteTest 3 ? drops in 1 minuteTest 4 drops in 1 minuteTest 5 ? drops in 1 minuteTotal ? drops in 5 minutes

Table 11-2Compute the average number of drops

per minute. We will consider this numberas the standard in Drop Time.

b. Copy and complete the followingusing your standard drop time:

Clock Time(1) 1 second(2) 1 minute(3) 1 hour

(4) 1 day(5) 1 year

Drop Time? drops

drops (standard).L drops or? kilodrops? kilodrops

kilodrops ormegadrops

Remember:1,000 drops = 1 kilodrop1,000 kilodrops = 1 megadrop

Table 11-3

c. How many drops in a megadrop?2. A'satellite orbits the earth in 90 minutes.

How long is this in Drop Time?3. Mariner IV took 22 pictures of the

planet Mars in 25 minutes.a. How long did it take Mariner IV to

take 22 pictures in Drop Time?b. How long did it take in Drop Time to

take 1 picture?4. What are some of the problems in keep-

ing time with drops of water?The measures we use effect our under-

standing of modern space science and tech-nology. The development of measurementand the instruments needed have grown asa matter of convenience. As the needarose for man to better understand theworld and to make measurements of "non-ordinary" distances, as in the solar system,man produced more precise instruments toobtain more accUrate measurements.

Long ago man was able to describedistance by his arms' width, a step orpace, or the width of his palm. Whenthere was little communication, the lengthof the measuring unit was' of little conse-quence: a trip along a trapping line, oneor two days; and winter, one or two monthsaway. It would not make much difference.

When families grouped into-tribes, tribesinto nations, and as nations came into con-tact with each other, communication ofmeasures was needed. With the railroad,automobile, airplane, radio, telephone, tele-vision, and satellite networks, man hasfound that it was necessary to standardizehis methods of measure. No longer couldhe pace off a distance, spread"' his arms,or measure the height of a wall with hishand; people of different sizes yieldedvarious results.

The method of defining these ancientunits has disappeared from daily use andin their place have come other methods.As detailed earlier, man's observations andability to .observe, have resulted in a sys-tem of units and standards used throughout

WIDTH OF A PALM

ca-

VOilOw

14.--"ti 401

1 ARMS WIDTH

1 PACE

Figure 11-6

Let us investigate the instruments andtechniques used to determine distance,scale, and time. A few thousand yearsago, man's ability to measure was de-termined by the precision of his eye. Whathe could see, he could estimate and there-fore measure.

ti

Figure 11-7

a. The Sun is brighter than the star, Polaris.the world. b. The pyramid is taller than the tree.

,

22

2 4

Early instruments were developed sothat man could measure more accurately.

Sextant(ANGLE)

Hour Glass(TIME)

Figure 11-8

Knotted Rope(DISTANCE)

He now could measure the mile to theyard, foot, inch, and fraction of an inch.Light could be measured in terms of thebrightness of the sun, candle, or color.Time could be determined in units of theyear, month, day, hour, minute, second,or fraction of a second.

More precise instruments enabled sci-entists to make observations that had notbeen possible before. Ancient theoriesgave way as new ideas were supported bymon accurate measurements.

By 1600, scientists began to specializeand to consider themselves primarily asphysicists, astronomers, biologists, chem-ists, and engineers. Each of the new sci-ences required special measurement tech-niques, and measurement became more'accurate.

LIPPERSHEY - TELESCOPE

VERNIER - VERNIER SCALE

TORRICELLI - BAROMETER

GALILEO - THERMOMETER

OERSTED - ELECTROMAGNET

NEWTON - SPECTROSCOPE

Scientists could measure positions on Eartli, distances between cities, and the diameter

of Earth.

LONGITUDELATITUDE

LOS ANGELES

NEW YORK

DISTANCE FROMNEW YORK 70 LOS ANCMLES

DIAMETER OFTHE EARTH

They could "Reach Out" into space and nr.r.-asure the diameter of the moon, the brightness

of the sun, and the tremendous distances tarrlhe stars.

235,000 MILES

itAADON

Figure II-11

He could more accurately determine the length of a year, the time of day, or the timeit "took" for a ball_ to drop from a tower.

SUMMER

SPRING

FALL

WINTER EASTSUNRISE

NOON

Figure II-12

slWESTSUNSET

Old ideas and concepts gave way to the new theories brought about by these approaches.

Ancient Theory

Earth FlatFixed

Planets Orbit the Earth

Atmosphere "4 ethers"

Modern Theory

Round, pear shaped,MovingOrbit the SunOxygen, nitrogen, CO2 , H2 0

Table 1I-4

In order to describe the measure ofobjects which cannot be seen or felt,today's scientists do not always think interms of the mile or the foot, the sun'sbrightness or the candle, the year or thesecond, but deal in fractions of units.Many scientists are concerned with distancessuch as of 0.00000001 centimeters (oneangstrom), light measured in terms of0.0001 candles (one ten-thousandth of acandle) and time in terms of the nano-second (0.000000001 seconds) one bil-lionth of a second.

Even with modern procedures, man'sability to measure depends upon the pre-cision of his instruments and his skill inreading or inteipreting these instrument&

Because instruments are subject to error,the scientist, as we do, must recognize thelimits of_his own ability.and of his measur-ing devices. One of the primary concerns ofthe scientist is to reduce experimental error.Errors are reduced by better technique andmore precise instruments.

We will riow see how scientists have re-fined their techniques and instruments inthe measurement of time, distance, andscale.

Time measurement must have had itsorigin in the mind of man as he watchedday follow night and the seasons nas& So,it is not surprising ,that man finally chosethe sun as the basis for measuring time.(Figure 11-13).

MIDNIGHT-M NNOON

Figure 11-13

From koollo driving the sun acrow thesky, to tire sun revolving around Earth,and to filially Earth revolving around thesun, man has utilized the periodic motionof Earth as an almost perfect "standare oftime. The basic units of time betcarre theday, the tnonth, and the year.

We accept the fact that Earth rotze=s onits axis once a day and Earth revolvesaround the sun once a year. But, what isa day? What is a year?

hi Figure 11-13, Earth makes one rota-tion from M to N to M every 24 hours.

S.:UN

Our day begins at midnight and ends atmidnight. Figure 1144 compares Earth toa giant 24 hour clock.

Point A, Figure 14, rotatms around thecenter of Earth, . C, and at -due end of 24hours it would have compled one rota-tion, or a circle.. For our punaoses, we willassume 360 degrees in a circle and noon.asour 00 and 24 hour point The mathe-matical symbol, for the wadi degree is °We are able to ielate hours of time to de-grees of a circile, lust as we -related hearttime to clock time as in Table II-1. For a

MIDNIGHT 12 0 or 24 NOON SUN

more detailed discussion of hours of timeand degrees of a circle, reference is made toanother book of this series, Shapes ofTomorrow, Chapter 3, pp. 61-64.

Do Ind confuse the terms minutes andseconds of arc with minutes and seconds oftime.

When speaking of angles, we say degreeof arc, or:

10 (one degree) of arc = 60'(sixty minutes) of arc

l' (one minute) of arc = 60"(sixty seconds) ef arc

Notice the symbol for minutes of arc is ',and the symbol used for seconds of arcis "

Earth Time

1 revolution24 hours

1 hour4 minutes1 minute4 seconds

of 0 hours, then 6 hours later at 6 P.M..,the sun is at an angle of 90° (or 6 hours.

1 holm. = 150_ 6 tours = 90°At 12:010 midnight, the sun is at an angleof 180° -or 12 hours. At 6 A.M., the sunis at an angle of 270° or LS Itours. At 12Noon, the sun is back at 0' -or0 hours. Wehave completed 24 hours or 360° .

We use the sun's posi6cm as seem fromEarth ari a reference for our :time. There-fore, When we give our loPal time, we areactually speaking of the angle of thesun_ This term is used by a=onorners andspace scientists to describe 'dime.

Consider Figure 11-16. Wa., are lookingdown at Eaxth from above tire North Pole,

Angle in degrees of arc

1-zircle

360 degrees15 degrees of arc

1 degree of arc15 minutes of arc

1 minute of arc

Table II-S

Trace the protractor at the end of thechapter. Cut it out and use it to measurethe angles in Figure II-15. Record youranswers. Compare your answers with thosegiven. How accurately do you measure?What can you say about your- instrument(the protractor)?

We an actually speak of time in terms ofan angle, Figure 11-14. If we use the positionof the sun at 12:00 noon as a starting point

N. Points A, B, C, D, and E represent satel-lite tracking stations. The hour angle ofthe sun from position A is 0 hours. There-fore, the time is 11:00 N-Oon. Conipare thehour angle of the sun from the other fourpoints. What dme is it at each position,when it is 12:00-Noon at Position A? SeeTable 11-6.

S UN

Figure II-16

Position

A

1;13,

Time

12:002:16 PM7:24 PM1:00 AM

10:30 AM

Angle of the Sun Hour Angle

0° 0'34° 0'

111° 0'195° 0'337" 30'

Table 11-6

5.a. Trace and carefully cut out the card-boamd earth, Figure 11-18. Center the=din over the circle below in FigureE-1.9. Push a straight pin or small paperfastener through point N on the earthanak-through the center of the circle asimlicated, so that the earth freely ro-tates around the pin. Align the arrowmarked New York, at 0 hours or12:00 Noon.

b. Whac time is it at New York? 12:00Noon.When is it 12:00 Noon at New York.(1) What time is it in Greenwich?(2) What time is it in Moscow?(3) What time is it in Tokyo?(4) What time is it in Los Angeles?

c. Rotate New York counter-clockwise90° or 6 hours.(1) What time is it now in New York?(2) What is the hour angle of the sun

from this position?With New York at this position, what

time is it now at:(3) Greenwich, England(4) Moscow, Russia(5) Tokyo, Japan(6) Los Angeles, California

d. (1) How many hours difference wasrepresented by rotating New York0° to 90°?

As you rotated New York from 00 to90°, how many hours did:

(2) Greenwich, England rotate?(3) Moscow, Russia rotate?(4) Tokyo, Japan rotate?(5) Los Angeles, California rotate?

e. Rotate New York in the same direc-tion, counter-clockwise, to 270° or

o hours 0 minutes2 hours 16 minutes7 hours 24 neinutes

13 hours 0 minutes22 hours 30 minutes

18 hours. Make a table like the onebelow and record the time now at:

Time Angle of the SunNew YorkGreenwichMoscowTokyoLos Angeles

Table 11-7

Note to student: We have been concernedwith only the hour angle ot the sun, there-fore, local time. We have not taken up thechange from one day to another, Mondayto Tuesday, etc., or standard time.

Figure IP! 7

As instruments improved and the ac-curacy of measurements increased, man be-gan to doubt the simple motion of hisplanet. As we found the pulse could not be

used as a standard for time, man found thatEarth was no longer an acceptable time.standard.

Observations of the stars created thefirst doubt of Earth's simple motion. Thestars appear to move i° farther to the westeach night. This is the same as saying a starrises four minutes earlier each night. Re-member from Table 11-5, we are able toshow that an angle of 10 is equal to fourminutes of time. We are able to explainthis observation by taking into accountEarth's revolution around the sun.

Figure 11-20

When Earth is at position A, Figure 11-20,the sun and a distant star are in a line asseen from M on Earth. Note that scale andangles are exaggerated for clarity. Afterone Earth rotation the star would appearto have returned to position M. However,Earth ha3 moved to position B due to itsrevolution around the sun. The Earth mustrotate about one degree or four minutesbefore the sun appears to return to positionM2. Therefore it takes 23 hours and 56minutes for Earth to complete a star day,sidereal day, and 24 hours to complete asun day, solar day.

A sidereal day = 23 hours 56 minutesA solar day = 24 hours

Another observatica which cast doubt onEarth as an accurate timekeeper was thatEarth's revolution around the sun did nottake 365 days but about 36514 days.Every four years a day is gained. This doesnot seem to be very important, but overhundreds of years we would find that theseasons would be confuse& Spring wouldbegin in the summer, summer in the fall,fall in the winter and winter in the spring.

Further it was finally discovered thatEarth's orbit around the sun was notcircular but a nearly circular ellipse as inFigure 11-21.

The Earth does not move at a uniformspeed as it revolves around the sun. At itsclosest approach to the sun, perihelion,Earth is at a distance of about 91,500,000miles from the sun. At its greatest distancefrom the sun, aphelion, Earth is about94,500,000 miles from the sun.

AphelionPerihelionAverage distance

94,500,000 miles91,500,000 miles93,000,000 miles

Table 11-8

The Earth is at perihelion in winter andat aphelion in summer. For purposes ofillustration, Figure 11-21 was constructedwith a greatly exaggerated elliptical orbitof Earth. One of the laws concerningplanetary motion states that a planet willmove faster in its orbit when it is closestto the sun and slower when it is farthestfrom the sun. As shown in Figure 11-21,again exaggerated, Earth moves from A toB in one day in January. It will move asmaller distance, C to D, in one day in July,

As previously shown, Figure 11-20, thedifference between the solar and siderealday is due to the distance that Earth re-volves in its orbit.

Although exaggerated, the distancetraveled from A to 13 in January is greaterthan C to D in July. Due to this difference,the solar day is somewhat shorter in Julyand longer in January. If we were keepingtime with a watch, we would find thesun would be about eight minutes be-hind the watch in spring and about eightminutes ahead of the watch in fall. Ourwatch time does not speed up in July orslow down in January. We keep time as

an average, or we speak of the average ormean solar day as 24 hours. Our clocksand watches which run at a uniform rateduring the year, actually keep average ormean time.

Another reason that solar days are notuniform in length of time is due to the factthat the axis on which Earth rotates is notperpendicular to the plane of Earth's orbit.This produces some interesting observa-tions in the sky. For the present it will besufficient to say that this phenomenonalone would cause the sun to be tenminutes behind a watch in February andAugust and ten minutes ahead in May andNovember.

By adding the effects of Earth's orbitand the axis of Earth, we arrive at trulycomplicated observations as in Table 11-9:

Month Minutes

February 15 minutes, watch behind the sunMay 4 minutes, watch behind the sunJuly 6 minutes, watch behind the sunOctober 16 minutes, watch ahead of the sun

Table 11-9

Apparent solar time was accurate enoughfor our ancestors. It is not nearly accurateenough for the aerospace age. With ourprecise instruments we have turned fromEarth's rotation, to a calculated averageor mean time.

Another early timekeeper was our near-est neighbor in space, the Moon. Man wasable to estimate the time of night fromthe appearance of the moon and its posi-tion in the sky. More recently, scientistshave investigated the moon not as a time-keeper, but as a landing place for Man'sfirst venture into outer space.

As you know, the moon orbits Earth atan average distance of about 240,000miles.

As illustrated in Figure 11-22, the moonpasses from position 1, to 2, to 3, to 4, andreturns to position 1 as it orbits Earth. Onelunar orbit takes about 30 days. Noticethe orbit of the moon is approximated as acircle. Remember a circle has 360°. Ifthe moon completes one orbit or 3600 in30 days, then it moves 12° in one day!

FIRST

QUARTER

SUN

NEW MOON

FULL MOON

Figure II-22

LASTQUARTER

360° 12° in one day30 daysIf the moon is at position 1, Figure 11-22,

seven and one-half days later it would be atposition 2. The moon would have moved7% days at 12° per day or 90° in 7% days.From position 2 it would move to position3, and it would be 90° from position 2, or180° from position 1. At position 3, themoon would have orbited 270° in 22%days. Returning to position 1, the moonhas completed a 360° orbit in 30 days.Each day the moon would appear to havemoved 12° in the sky.

Look again at Figure 11-22. When themoon is at position 1, the moon is betweenthe sun and Earth. As the moon passes be-tween the sun and Earth, one of threethings occurs as shown in Figure 11-23.

Throughout the year, as the moon orbitsEarth (Figure 11-23) it can appear to passabove the sun, a; below the sun, c; or di-rectly between the sun and Earth, b. Posi-tions a and c occur most frequently.Position b infrequently occurs. What dowe call the phenomena when the moonpasses directly across the disc or face ofthe sun as in position b? In any event,position a, b, and c, m Figure 11-23 could

Figure 11-23

represent the moon at position 1 in Figure11-22. Therefore once each month the moonaoes appear to pass "between" the sun andEarth. Why don't we notice this when itoccurs? We only "see" it occur when themoon is at pOsition b (Figure 11-23).

Again refer to Figure 11-22. If we arelooking from Earth at the moon, position1, we are looking directly into the sun.Can you see any object in the sky in thedaytime except for the sun?

N ORT H PO LEFigure 11-24

FIRSTQUARTER

NEW MOON

THIRDQUARTER

FULL MOONFigure 11-25

When the moon, sun and Earth are inposition as illustrated by Figure 11-24, thelighted side of the moon is the side towardthe sun. Besides being in the daytime sky,we are looking at the dark side of themoon. Can we see the moon as illustrated_in Figure 11-24? No It would be in thesky, but we could not see it.

When the moon is at position I, (FigureII-25) we refer to the moon as a new moon.Seven and one-half days later, when themoon is at position 2, the moon is referredto as the first quarter. The 15 day oldmoon at position 3, is called the full moon.At position 4, 221/2 days after new moon,the moon is called the third quarter. 71/2

days after third quarter or. 30 days afternew moon, the moon is back at position 1and is again referred to as the new moon.

When speaking of the moon, usefulterminology is illustrated in Figure 11-26.As the lighted side of the moon visiblefrom Earth becomes larger, new moon tofull moon, the moon is said to be waxing.As the lighted side-as seen from Earth be-comes smaller, full moon to new moon,

CNEW WAXING WAXING

CRESCENT 1st QUARTERWAXING FULL WANINGGIBBOUS GIBBOUS

Figure11-26

33

ta4

WANING WANING3rd QUARTER CRESCENT

NEW

the moon is said to be waning. If themoon's lighted side as seen from Earth islarger than a quarter and smaller than full,the moon is said to be gibbous. If thelighted side of the moon as seen fromEarth is less than a quarter but greaterthan when at new moon the moon is saidto be a crescent.

Why is the quarter moon called quarter?How much of the moon is always lightedby the sun? 1/2. How much of that lightedhalf do we see at the quarter phase? 1/2.

1/2 - 1/2 =1/4, or we see 1/4 of the moon's surfaceat the quarter phases. Using the vocabularypreviously described, let us attempt to de-scribe where the moon "goes" in thedaytime.

To better understand the "wanderings"of the Moon and to use the moon as a time-keeper we will make two assumptions.First, we will tell time by the position ofthe sun, and second, we will assume thatthe sun rises into the eastern sky at 6:00 AM,is directly south in the sky at 12:00 noon,an-cl-sets in the west at 6:00 PM (Figure11-27).

1200 NOON

EAST6:00 AM

WEST6:00 PM

You are facing south in Figure-rH-27.East is to the left and west-is-to the right.The sun is high in the sky, directly south.What time is it in Figure II-27? 12:00 Noon.What time did the Sun rise on this day?6:00 AM. What time does the sun set on .

this day? 6:00 PM. If the sun rises at6:00 AM and sets at 6:00 PM, how manyhours does the sun spend in the sky on thisday? 12 hours. How many hours do we seethe sun this day? 12 hours. We see the sunall day unless, of course, it's cloudy orraining. We will assume clear days andnights.

In Figure 11-27, we observe the moon atthe phase we described as new moon. Re-

member when the moon is at this positionin its orbit, the moon is passing "between"the sun and Earth. Figure 11-27 illustratesthe moon passing below the sun's positionas seen from Earth. Read the followingquestion slowly. Reread it. If thesun is directly south at 12:00 noon,and the new moon is directly southwhen the sun is directly s--Outh, what time-is it when the new moon is in the south?12:00 Noon. Remember we tell time bythe position of the sun! , If the new moonis directly south at 12:00 noon, what timewas it when the new moon rose in the east?6:00 AM. If the new moon rises at 6:00AM, is directly south at 12:00 noon, whattime does it set? 6:00 PM. Or we say thenew moon sets when the sun Sets.Do you see the new moon set? No. Thenew moon sets in the fading light of thesun. The new moon rises at 6:00 AM andsets at 6:00 PM. How many hours is thenew moon in the sky? 12 hours. Howmany hours do you see it on this day?You don't. It is only in the sky whenthe sun is in the sky. Also recall that itnew moon we are observing the dark sideof the moon. The lighted side is towardthe sun. (Figure 11-24).

Therefore the new moon phase is thephase of the moon that we cannot see.It is not visible to the unaided eye. Thenew moon is only in the sky in the day-time. It has already set in the west beforedarkness and is not seen in the nighttimesky.

New Moon

Rises 6:00 AMSe ts 6:00 PMHours in the sky 12 hoursIs seen 0 hours

34

:40

Figure 11-28, represents the moon threedays after new moon. The moon has moved3 days or 36° in its orbit around Earth.What time is represented by Figure 11-28?12:00 Noon. The sun is due south. If thesun rises at 6:00 AM and sets at 6:00 PM,what time did the moon rise in Figure11-28? 9:00 AM. The moon is about threehours "behind" the sun. Did you see themoon of Figure 11-28 when it rose in the.east? No. It is daylight at 9:00 AM. Ifyou are outside looking at the moon inFigure 11-28, could you see it? No. Thetime is 12:00 Noon.

Figure 11-29

Figure 11-29 represents the ,3 day oldmoon at sunset, 6:00 PM. Do you see the3 day old moon at sunset? Yes. The moonhas moved out of the glare of the sun.What time will the 3 day old moon set?9:00 PM. If the 3 day old moon rose at9:00 AM and sets at 9:00 PM, how manyhours is it in the sky? 12 hours. Howmany hours do you see it? 3 hours. It isobserved from 6:00 PM until 9:00 PM whenit sets in the west. Could you observe the3 day old moon at 12:00 midnight? No.It has already set.

The three day old moon is considered acrescent as it is between the quarter moonand the new, moon phase. The three dayold crescent moon is said to be waxing.The lighted side is becoming larger as themoon is moving from the new mo6n to fullmoon phase. The moon at this position inits orbit is then described as a 3 day oldwaxing crescent moon.

3 Day, Waxing, Crescent Moon

Rises 9:00 AMSets 9:00 PMHours in the sky. . 12 hoursIs seen 3 hours, 6:00 PM to

9:00 PM

35

EAST

Figure 11-30WEST

In Figure 11-30 the sun is setting in thewest. What time is it? 6:00 PM. The 71/2day old first quarter moon is directly southin the sky at sunset. What time is the firstquarter in the south? 6:00 PM. If thefirst quarter moon is in the south at 6:00PM, what time did it rise? 12:00 Noon.Did you see it when it rose in the east?No. The sun was high in the sky. Whattime will the first auarter moon set?12:00 Midnight. Will you see it as it sets?Yes. It is night. If the first quarter moonrises at 12:00 noon and sets at 12:00midnight, how many hours is the firstquarter moon in the sky? 12. hours. Howmany hours do you see it? 6 hours. Thefirst quarter moon is observed from sunsetuntil it sets about midnight.

Waxing First Quarter

Rises 12:00 NoonSets 12:00 MidnightHours in the sky. . . 12 hoursIs seen 6 hours, 6:00 PM to

12: 00 Midnight

EAST WEST

Figure 11-31

Figure 11-31 represents the 10 day oldwaxing gibbous moon. The ten day oldgibbous moon is about 9 hours "behind"the sun. The sun is setting in Figure 11-31and the gibbous moon is toward the south-east. What time did the waxing gibbousrni:Jon rise? 3:00 PM. Did you see it rise?

No. What time will it be in the south?9:00 PM. What time will it set? 3:00 AM.Do you see it as it sets? Yes. If it rises at3:00 PM and sets at- 3:00 AM, how n. ?myhours is it in the sky? 12 hour How manyhours is it visible? 9 hours.

10 Day, Waxing Gibbous Moon

RisesSetsHours in the sky.Is seen

3:00 PM3:00 AM12 hours9 hours, 6:00 PM to

3:00 AM

EASTFigure 11-32

In Figure 11-32 the full moon :Is risingas the sun is setting. Notice that the fullmoon is opposite the sun in the sky, tw,.:Ivehours "1$0.1ind" the sun. What time isillusirated :cry Figure II-32? 6:00 PM.. Thesun is setting. If the full 15 day moon risesat 6:00 PM, do you see it as it rises?Yes. The sun is setting. The full moonrises as the sun sets. What time will the fullmoon be directly south? 12 Midnight.What time will the full moon set? 6:00 AM.The full moon sets as the sun rises. Howmany hours is the full nloon in the sky?12 hours. How many hours do you see it?12 hours. The full moon is seen all nightfrom sunset to sunrise.

Full Moon

Rises 6.00 PM. . . . . . . . .... 6:00 AM

Hours in the sky 12 hoursIs seen 12 hours, sunset to

sunrise

Notice in Figure 11-33 that the sun isrising. What time is it? 6:00 AM. If the18 day old waning gibbous moon is in thesouthwest at sunrise,, what time was it due

36

Figure 11-33

south? 3:00 AM. What time did it rise inthe east? 9:00 FM. Do you see it as itrises? Yes. If the 18 day old waninggibbous moon rises at 9:00 PM, what timewill it set? 9:00 AM. Will you see itwhen it sets? No. It will disappear fromview in the southwest as 'the sun rises inthe east, setting three hours later.

15 Day, Waning Gibbous Moon

Rises 9:00 PMSets 6:00 AMHours in the sky. . . 12:00 hoursIt is seen 9 hours, 9:00 PM to

6:00 AM

Figure 11-34

Figure 11-34 represents the waning thirdquarter moon.

Exercises: See if you can answer thesequestions without looking backat the various figures.

6.a. The sun is rising in the east, thereforethe time indicated in Figure 11-34 is

b.

C.d.

e.f.

The third quarter moon is directlysouth at orThe third quarter moon rises atDo you see the third quarter moonrise?The third quarter moon sets atDo you see the third quarter moonset?

g. How many hours is the third quarter 8.a. Identify the following phases and themoon in the sky? approximate time. In all cases you

h. How many hours do you see it? are looking south.i. The third quarter moon is seen from

toj. If a quarter moon is observed in the (1) (2)

sky at 10:30 PM, is this the waningthird quarter?

k. 22 day old, waning third quarter?(1) Rises(2) Sets(3) Hours in the sky(4) It is seen hours,

fromto FULL MOON PHASE_

TJME- 9:00 PM

EASTFigure 11-35

WEST

Figure 11-35 represents the 27 day oldwaning crescent moon.7.a. What time is indicated by Figure II-35?

b. In what direction is the crescent moonin Figure 11-35?

c. What time did the waning crescentmoon rise?

d. Did you see it when it rose?e. What time is the waning crescent in

the south?f. What time does the waning crescent

set?g. Do we observe the waning crescent

moon setting?h. How many hours is the waning crescent (2)

moon in the sky?i. How many hours do we see it?j. 27 day old, waning crescent moon:

(1) Rises . ..(2) Sets(3) Hours in the sky(4) Is seen hours,

fromto

(3)

b.

WAXING GIBBOUS

Figure 11-36

IDENTIFY PHASE, TIME OR DIRECTION

The m-Oon continues in its orbit. As themoon again passes "between" the sun andEarth, the moon returns to the new moonphase and the lunar cycle is repeated.

37k.:5":,

38 r

WANING CRESCENT PHASE -TIME _ 6:00 PM

SOUTHEAST SOUTHWEST

Figure 11-37

Caution: In the previous section, we havestated that you cannot "see" the moon inthe daytime sky. However, there are timeswhen you can see the moon when the sun isstill in the sky. This occurs when the moonis near the full phase. This is due to the sun'slight being bent, refracted, as it passesthrough Earth's atmosphere. At this time,tile brilliant moon stands out against thedeep blue of the early evening or earlymorning sky.

Figure II-38

In the precedhig sections, we have seenthe development of the measurement oftime. We will now apply the same basicprinciples and procedures to the directmeasurement . of distance, and later t6indirect measurement of distance with aScale.

Current methods of measuring ordinarydistances are fainiliar to all of us. How-ever, with recent advances in the space sci-ences, the need to measure accurately be-comes exceedingly important. Let usconsider the line below, Figure 11-39.

You could estimate that the line wasless than a foot, a few inches, or between3 and 4 inches. You could do-this by basicobservation, and if this served our purposes,.this is an acceptable answer. However, tomake a more accurate measurement thanthis, we would use a standard ruler. (Atthis point, you should copy and cut out thestandard rule7 inches; and metric ruler,centiineters, found at the end of thechaptel.) Measure the length of the linewith the standard ruler in inches. Theresult of your measurement indeed showsthat the line is less than a foot, it is a fewinches in length, and is in fact between 3and 4 inches. With the ruler, you can de-scribe the length of the line more ac-curately than with your eye. You are nowable to describe the line as being between3%2 and 4 inches. You could also say moreaccurately that the length of the line wasbetween 3 3/4 and 4 inches. A table ofyour measurement steps could be as fol-lows:

MeasurementStep

1

23

Greater than Less than

3 inches 4 inches3 1 /2 inches 4 inches3 3/4 inches 4 inches

Repeating your measurement with acentimeter ruler the following informationcould be obtained:

MeasurementStep Greater than Less than

1 9 centimeters 10 centimeters2 9.5 centimeters 10 centimeters3 9.7 centimeters 9.8 centimeters

or 97 millimeters or 98 millimeters

Table II-10

To attempt to read our measurements as3 7/8 inches or 97.5 millimeters, would beto exceed the precision of our instrument.in this case, the ruler. Errors to be con-

Figure 11-39

38

sidered in a measurement experiment suchas this would include:

a. The width of the printed line on theruler

b. The angle from our eye to the rulerc. Texture of the paperd. Placement of the ruler on the printed

page.If it were necessary to make a more

accurate measurement, we would turn to amore precise instrument, for example, avernier scale. This device enables us to de-termine the length of the line with a greaterdegree of accuracy.

VERNIER SCALE0 1 2 3 4 5r 'it e `1- '1 I

0 1 2 3 4 5 6 7 8 9 10PRIMARY SCALE

Figure 11-40

The vernier scale is a common attachmentto measuring instruments, such as the ruler,micrometer, or protractor. The vernier isused to determine a fraction of division onthe main scale that is the primary scale asin Figure-II:40. Vernier graduations aredifferent from the primary scale, but beara simple relation to it. For example, thevernier represented by Figure 11-40 is soarranged that it reads 0.2 or 1/5 of a divi-sion on the primary scale. In order to makea reading like this, five divisions on thevernier scale must equal four diviNions onthe primary scale (Figure 11-41). Eachvernier scale division is equal to 4/5 of aprimary scale division. The difference inthe length of the divisions is ealled the"least count" of the vernier. By using theprinbiple of "least count," we could con-struct a vernier to read 1/32 or 1/64inches, or 0.5 millimeters, 0.1 millimeters,and so on.

0 1

0 1

VERNIER SCALE

2 3 4

1

1 I

2

PRIMARY SCALE

,F4gure 11-41

4

39

VERN IER SCALE

0 1 2 3 4 5'V1111111 III Io 2 3 4 5 6 7 8 9 10

PRIMARY SCALE

Figure 11-42

In reading the vernier measurement ofthe penny in Figure 11-40 two readings mustbe taken. The first reading is to determinethe position of the vernier 0 on the primaryscale. Prior to the measurement, the vernier0 is at primary 6, (Figure 11-42). Then toread the diameter of the penny, Figure11-40, the vernier 0 is between 2 and 3 unitson the priinary scale. This tells us that thediameter of the penny is between 2 and 3units. The second reading will determinethe fraction of the scale unit. In this read-ing, we must determine which vernier divi-sion coincides most directly with a primary_scale division. Upon inspection of FigureH-40, we- see that the vernier scale isarranged as follows:

Vernier Scale Primary Scale0 falls between 2 and 31 falls between 3 and 43 coincides with 54 falls between 5 and 65 falls between 6 and 7

Vernier 3 coincides with a primary scaledivision, and therefore, is the division whichrepresents the fraction of a primary scaledivision. If one vernier division is equalto0.2 of a scale division, then three vernierdivisions equal 0.6 of a primary scale divi-sion. Our actual reading is obtained byadding the vernier reading to the primaryscale reading.

Primary ReadingVernier ReadingDiameter of penny

2.0. unitsO. 6 units2.6 units

In this manner, we are able to directlymeasure the diameter of the penny with ahigh degree of accuracy by making use ofan instrument of greater precision than astandard rule.

At this time, the student should care-fully read the directions below and then

copy and cut out the vernier at the end ofthis chapter.Directions:

Carefully:(1) Copy and cut out the vernier(2) Cut along Line C to A(3) Cut along Line B to AThe vernier scale should slide freely and

evenly along the primary scale. The smallestunit on the main scale is 14" or 8/32 inches.The vernier scale is read in 1/32 inches.This vernier is read the same way as out-lined above. The primary scale is read to thenearest 1/4 or 8/32 iziches plus the vernierreading up to 7/32 inches.Example: Place the vernier over the linein Figure 11-39. We are able to see that thevernier 0 is between 3 3/4, that is 3_24132,and 4 inches. The vernier 3 coincides mostclosely with a primary scale division. Theline then measures 3 24/32 inches + 3/32inches or 3 27/32 inches.

It should be noted that this measurementis more accurate than the measurement ob-tained with the standard ruler or vernierprimary scale because the vernier is moreprecise than the ruler. However, it againshould be noted that the same kinds oferrors involved with the ruler measurementare included with the vernier measurement.In this case, the errors are more critical be-cause of the accuracy of the measurement.In actual practice, vernier scales have beendesigned to measure to the nevrest 0.001inches (one-thousandth of an inch).

Let us approximate one of the funda-mental distances of astronomy, the astro-

nomical unit. The astronomical unit, A.U.,is the average distance bitween the center ofthe sun and the center of Earth. Astrono-mers have spent hundreds of years in ob-serving and calculating to refine this basicmeasurement.

Figure 11-43 represents Earth's orbit ofthe sun. It is drawn to scale, I" equals48 million miles. To simple inspection,the orbit of Earth appears as a circle.If we were to carefully measure Figure11-43, we would fmd that Earth's orbitis not a circle, but elliptical, slightly oval.If we were to report our measurementof the astronomical unit to a group ofscientists, we would include in our report:

1. Aphelion2. Perihelion3. Average distance from the sun4. Eccentricity of Earth's orbit

The above four characteristics are reterredto as the primary orbital elements pertain-ing to the shape of Earth's orbit. Fromthese four elements, a scientist couldproduce our drawing of Earth's orbit.

Aphelion miles

Perihelion miles

Average Distance miles

Eccentricity miles

To determine Earth's farthest point fromthe sun, aphelion, we would measure thedistance from the sun, (s) to El (Figure

S.

SUN

Figure 11-43

40

11-43). This_distance is 1 31/32 inches. If.1 inch equals 48 million miles, then1-31/32 inches equals 94,500,000 miles.At E1, aphelion, Earth is 94,500,000miles from the sun. To determine Earth'sclosest point to the sun, perihelion, wewould measure the distance from the sun(s) to E2. This distance is 1 29/32 inches.With a scale of 1 inch equals 48 millionmiles, 1 29/32 inches equals 91,500,000miles. At E, , perihelion, Earth is 91,500,-000 miles from the sun. To determine theaverage of Earth's distance from the sun,we could add the aphelion distance to theperihelion distance and divide the sum bytwo. This would give us Earth's averagedistance as 93,000,000 miles. However,to reduce the possibility of error due tomeasurement, we could take a number ofmeasurements around Earth's orbit.

Figure 11-44

If we made the indicated measurements At this point we havein Figure 11-44, we would tabulate the re-sults in a table as follows: Aphelion 94.5 x 106 miles

Perihelion 91.5 x 106 miles

Average distance 93.0 x 106 miles

1 A.U. = 93 mi:iion miles, 93.0 x 106 miles

Table II- 12

The eccentricity of Earth's orbit is a meas-ure of the "roundness" of the orbit orellipse. If Earth's orbit was a perfectcircle, the eccentricity would be 0. Theeccentricity of an ellipse is always less than

Measurement Altitude Scale In che s

1 a-s 1 31/32

2 b-s 1 31/323 c-s 1 30/324 d-s 1 31/325 f-s 1 29./32

6 E2-s k 28/32'7 g-s 1 29/328 h-s 1 29/329 i-s 1 29/32

10 j-s 1 31/32

11 k-s 1 31/32

12 E1 -s 1 31/32

Sum = 23 8/32

Table II-11

If we were to sum the 12 measurements,and divide by 12, we would have anaverage, or mean Earth-sun distance of:23 8/32/12 = 1 30/32 = 1 15/16 inches.

From the scale, one inch equal to 48million miles, 1_15/16 inches equals 93million miles.

4 1

1. The closer the eccentricity to 1, themore elliptical the orbit.

Figure.11-45

For purposes of illustration, the ellipticalorbit of Earth has been exaggerated inFigure 11-45. Notice that the sun is notat the center of the ellipse, C. The Earth atposition Ei is at aphelion at a distance fromthe center of the sun of A. The Earth inposition E, is at perihelion at a distance ofP from the center of the sun. We are ableto express the eccentricity of Earth's orbitin terms of the aphelion (A) and perihelion(P) distances.

A - PEccentricity, e =A + P

94,500,000 - 91,500,000e 94,500,000 +91,500,000

3,000,000 3 1e

186,000,000 186 63

e = 0.016

Since the eccentricity is small, 0.016,as compared to 1, we know Earth's orbitis nearly circular.

To interpret these results, consider theaccuracy of our measurement. Your vernieris able to measure to the nearest 1/32 ofan_ inch. Therefore, each measurement issubject to an error of 1/32 inches (1/64inches below the value and 1/64 inchesabove the value). Thus, the measure-ment, in the case of average Earth-sundistance 1 15/16 inches, should be written1 15/16 ± 1/64 inches. If we were to con-vert this number to mile's, 1 inch equals48,000,000 miles, we would show that theaverage Earth-sun distance to be 93,000,000± 750,000 miles. Our report of the primary

orbital elements of Earth would now appearas:

Aphelion 94.5 x 106 ± 7.50 x 103Average Distance 93.0 x 106 ± 7.50 x 103Perihelion 91.5 x 106 ± 7.50 x 103Eccentricity 0.016

The astronomical unit, A.U., would havea value of 93 x 106 miles plus or tninus7.50 x 103 miles. With today's standards,our measurements of Earth's orbit are notvery realistic and are subject to error.

With the advent of the space age, manhas continued to refine this basic measure-ment. Table 11-13 illustrates some recenthistory of the measurement of the astro-nomical unit.

If we were to report the orbital elementsof a satellite, we would report the samefour primary characteristics as we did forEarth's orbit. For satellites which orbitEarth, we refer to the highest point in orbitas apogee and the low point as perigee.Apogee and perigee are measured from thecenter of Earth, but generally are reportedfrom the surface of Earth.

Although scientists measure and maketheir calculations based on the satellite'sdistance from the center of Earth, thealtitude of a satellite is reported to thegeneral public as the average distance of thesatellite from the surface of Earth.

That is to say, altitude of Echo I isreported as 1,000 miles and not as 4,960miles.

Si is a satellite at apogee at a distance Afrom the center of Earth. S2 represents theperigee of the satellite at a distance of Pfrom the center of -Earth, Figure 11-46.

SATELLITE

Figure 11-46

42

Number

Source ofmeasurement

and data

A.U. inmillionsof miles

Experimenter's Estimate ofA.U. value range

1 Newcomb, 1895 93.28 93.20 - - - - 93.35

2 Hinks, 1901 92.83 92.79 - - - - 92.87

3 Noteboorn, 1921 92.91 92.90 92.92

4 Spencer Jones, 1928 92.87 92.82 - - - 92.81

5 Spencer Jones, 1931 93.00 92.99 - - - 93.01

6 Witt, 1933 92.91 92.90 - - - - 91.92

7 Adams, 1941 92.84 92.77 - 92.928 Brower, 1950 92.977 92.945 - - - - 93.008

9 Rabe, 1950 92.9148 92.9107 - - - - 92.9190

10 Millstone Hill, 1958 92.874 92.873 - - - - 92.875

11 Jodrell Bank, 1959 92.876 92.871 - - - - 92.882

12 S. T. L., 1960 92.9251 92.9166 - - - 92.9335

13 Jodrell Bank, 1961 92.960 92.958 - - 92.96214 Cal. Tech., 1961 92.956 92.955 - - - 92.957

15 Soviets, 1961 92.813 92.810 - - - - 92.816

Table 11-13

Example: Echo I was orbited in August of1960. Apogee was measured as 5,010miles and perigee as 4,910 miles. What arethe four primary elements as to the shapeof the orbit? (Use 3,960 miles as theaverage Earth radius)

Apogee = 5,010 - 3,960 = 1,050 miles

Perigee = 4,910 - 3,960 = 950 miles

Average 1,050 + 950Distance 2

1,000 miles

5,010 4,910 100 0.01Eccentricity ,010 + 4,910 9,920

Apogee = 1,050 milesPerigee = 950 milesAverage Distance = 1,000 milesEccentricity = 0.01

Table 11-14

Exercises:9. Explorer 1, the first United States

satellite launched January 21, 1958, hadan apogee measured to be 5,533 milesand a measured perigee of 4,184 miles.Report the four primary orbital elementsas to the shape of the satellite's orbit.

a. Apogee milesb. Perigee milesc. Average Distance milesd, Eccentricity

Table II-15

10. Explorer III launched June 28, 1958,had a reported apogee of 1,740 milesand a reported perigee of 118 miles.What are the four primary orbital ele-ments as to the shape of the orbit?

a. Apogee milesb. Perigee milesc. Average Distance milesd. Eccentricity

Table II-16

Thus far we have been concerned withdirect measurement of distance and time.We can now extend these ideas to indirectmeasurement with a scale.

43

44

Figure 11-47

Earth BasedPhotograph

e)

_."1, 10

Figure 11-47 shows the surface of themoon as photographed from Earth. Figure11-48 is of the same area of the moon asphotographed by Ranger IX on March 24,1965.

These photographs are of particular In-terest because Earth based measurementsof Ptolernaeus (the large crater at the top ofboth photographs) estimate the average

44

4

Figure 11-48

Ranger IXPhotograph

diameter to be over 90 miles. Analysisof Ranger's IX pictures determined theaverage diameter to be about 94 miles. TheEarth based picture represented by Figure11-47 was taken at a distance of about240,000 miles and Figure 11-48 whenRnnger TX was about 470 miles from thesurface of the rrmon.

In both instances and using similarmethods, scientists were able to concludethat the diameter of Ptolemaeus was about90 miles. Although the moon is seen bythe unaided eye at a distance of 234,000miles and wIth a first class telescope at anequivalent distance of 500 miles, Ranger'scameraa "see" it at an equivalent distanceof 1/2 of a mile.

The best Earth-based photograph is ableto resolve, see clearly, lunar surface featuresas small as 1,000 feet. Later we shall com-pare this figure with the resolution ofRanger IX photographs.

You can use Ranger photographs to esti-mate size and distance on the moon, if youunderstand the grid system of the Rangercamera.

...r.-6z_07:20

SCALE-___ ICENTRAL RETICLE

i

,..L

Figure 11-49

The grid system is superimposed on thecamera face. The grid crosses of Figure11-49 are called reticles, (vet'-i-kels). Thecenter cross mark on the camera face iscalled the central reticle. Grid north isdefined as a straight line drawn from thecentral reticle to the middle reticle in thenorth margin. Grid north differs from truelunar north depending upon spacecraft posi-tion, camera attitude, and the altitude ofRangel above the moon.

Actual distances on the moon can becalculated from the camera scale. The scaleis the ratio of the distance between thecentral reticle and the reticle immediatelyto the left and the distance vizible betweenthe two points on the lunar surface. In the

actual analysis of Ranger photographs,there are both north-south ..7cl east-westscales.

The scale also changes as we measuretoward the margin of the photograph dueto the curvature of the moon, the cameraangle, and the longitude of the photo-graphed region. For our purposes ofillustration, we will assume a flat surface,make measurements with an average scaleand assume north-south and east-west scalesto he equal.

Now we will examine in detail two majorcharacteristics affecting our use of theRanger camera grid system: camera angleand satellite altitude. The camera angleis the view of the moon as seen from aparticular camera, such as camera A, ofRanger IX. This instrument was built fora camera angle of 25°. Figure 11-51 repre-sents Ranger IX as it approached thesiirface of the moon and is drawn to scale,1 inch equals 250 miles. At an altitude of1,300 miles, Camera A with a field ofview of 25° would "see" a circular area ofthe moon as in Figure 11-50.

Camera A uses a mask on the lightsensitive electronic tube in place of camerafilm. The resulting image of the moon isthe portion of the full 250 view representedas the shaded area in Figure I1-50.

The area of the moon's surface seen byCamera A's tube would depend upon thealtitude of the satellite. The altitude,Figure 11-51, is the distance from the spacecraft to the surface directly below. At an

1300 MILES A

25°

500 MILES D

Figure II-31

altitude of 1,300 miles, Position A. Figure11-51, Ranger IX viewed a square about492 miles o side, BC. This is a surfacearea of the moon of 492 miles by 492miles or 242,064 square miles and couldresolve features of 2,600 feet. At an alti-tude of 500 miles, position D, Ranger IX'scamera A could photograph a square ofabout 186.8 miles on a side, EF, or asurface area of 186.8 x 186.8 or 34,394square miles. At this altitude, Camera Acould resolve surface features of 1,000feet.

As the altitude continues to decrease,the area photographed decreases, and theresolution increases. We could compileour data as in Table 11-17.

These figures are approximations andwill afford us a general understanding ofthe scientific principles of measurementunderlying the successful Ranger mis-sions.

Remember at an altitude of 1,300 miles,the camera is able to view a square approxi-mately 492 miles on a side. The 492miles represents the distance from thereticle on the left margin to the reticle atthe right margin. The distance representedbetween two reticles, average scale, wouldbe 492 miles divided by 4 or 123 miles.This distance is represented by 1 5/8 inches.Therefore, 1 inch would equal 76 miles.We-may set up a table for scales at variousaltitudes, Table II-18.

Ranger 9

Altitude (Miles)

Camera A

Surface area(Square miles)

Camera Angle 25°

Resolution(feet)

1. 1300 242,064 2,6002. 500 34,894 1,0003. 250 10,000 5004. 100 1,697 2005. 4.5 4 9

Altitude(miles)

Length of side(miles)

Average Scale(neles)

1 inch equals(miles)

1300 492.0 123.0 76475 186.8 46.7 29250 100.0 25.0 15

100 4L2 10.3 6.44.5 2.0 0.5 0.3

Table II-18

Refer to Figures 11-47 and 11-48. Thethree large craters found in the photo-graphs are Ptolemaeus (top center),Albategnius (lower right), and Alphonsus(lower left). The scale for Figure 11-47 is1 inch equals 80 miles.

Use your standard ruler to measure thediameter c,f the crater Ptolemaeus. A closeestimate of the diameter from rim to rimwould be 1.2 inches. To calculate thediameter of Ptolemaeus in miles:

1 inch 1.2 inches80 miles X miles

x = 80 - 1.2x = 96 miles

The scale for Figure 11-48, a Rangerphotograph, is 1 inch equals 65 miles.Measure Ptolemaeus in Figure 11-48 withyour ruler. You will find the diameter tobe 1.4 inches. Calculating the diameter inmiles,

1 inch 1.4 inches65 miles X miles

x = 65 x 1.4x = 91.0 miles

We repeat the procedure for the cratersAlphonsus and Albategnius and record themeasurements in Table 11-19.

Comparing the results of the measure-ments, we find that the diameter of thecraters in Figure 11-47 varies from thoseobtained in Figure 11-48. We can attributethe variation in your mzasurement to:

a. One measimementb. Irregular shaped cratersc. Problem in determining the rim of the

craterd. Black and white shadinge. Not measuring throug;1 the center of

the crater

Scale1 inch =

ScaleDiameter Diameter

PtolernaeusEarth 80 miles 1.2 inches 96.0 miles

Ranger 65 miles 1.4 inches 91.0 miles

AlphonsusEarth 80 miles 0.75 inches 60.0 miles

Ranger 65 miles 0.9 inches 58.5 miles

AlbategniusEarth 80 miles 0.9 inches 72.6 miles

Ranger 65 miles 1.1 Inches 71.5 miles

Table II-19

Figure 11-52

To reduce the occurrence of experi-mental error, we can repeat thy, procedurewe used in determining the astronomicalunit earlier in this chapter. in this manner,we would speak of the average diameter of

the crater. This value would certainly bemore representative and better understood.

Measuring ten random diameters of eacnof the craters in Figures 11-47 and 11-48,we colledt our data as follox .s, Table 20:

Ftolemaeus'Dial Earth-based Ranger

AlphonsusEarth-based Ranger

AlbategniusEarth-based Ranger

1- 1.20 1.30 0.75 0.90 0.90 1.10

2- 1.15 1.40 0.80 0.95 1).85 1.20

3- 1.10 1.40 035 1.00 1.00 1.30

4- 1.00 1.45 0.80 L10 0.95 1.35

5- 1.10 L50 0.85 1.05 1.00 1.20

6- 1.15 1.40 0.80 0.95 0.90 1.05

7- 1.20 1.30 0.80 1.00 1.05 1.15

8- 1.20 1.45 0.70 1.10 1.00 1.10

9- 1.10 1.50 0.75 1.05 1.00 1.10

10- 1.15 1.40 0.80 1.00 0.95 1.20

Total 11.35 14.10 7.80 10.10 9.60 11.75

Total 11.35 14.10 7,80 10.1 9.60 11.75

No. of Trials 10 10 10 10 10 10

Average Diameter(Inches) 1.13 1.41 0.78 1.01 0.96 1.17

Average Diameter(Miles) 90.4 91.0 62.4 65.'t 76.8 6.1

Table 11-20

48

HEIGHT OFMOUNTAIN

Ey this procedure, our figures moreclosely agree with each other. Using thisprocedure to determine the average diam-eters of the craters, we have tended to reducethe possibility of experimental or randomerror. The greatest possibility of error inour determinations would be a constanterror. To reduce the constant error, wewould go back over our procedures and re-check our determinations of:

a. Calibration and precision of measur-ing instruments

b. Distance to moonc. Calculation of scaled. Determination of the center of the

cratere. Dennition of rim of tlie craterBy continuing to refine our procedures

and calculations, we continue to increasethe accirracy of our measurements.

Using the same basic procedure, we areable to calculate the approximate altitudeof the mount lins on the moon. Turn toFigure 11-58. The mountain in the photo-graph is referred to as the central peak ofAlphonsus. The scale on this photographis 1" equals 6.4 miles. When the photo-graph was taken, the sun was at an angle of110 to the surface of the moon. You canmeasure the length of the shadow as 0.5inches. Our scale drawing would appear assFigure 11-53. For purposes of illustration,wc magnify our scale 6 times or say, 3".equals 3.2 miles.

From Figure 11-53, you. are able to de-termine La as 110, the angle of the sun.The line AB represents the length of theshadow f the mountain, 3 inches or 3.2miles. Line CB represents the altitude ofthe mountain. If you measure CTI, youfind it is 5/8 inches long. We determirothe approximate ahitude of the mountainas follows:

3 inches 3.2 miles5/8 inches X miles

5/8 3.2X

3

X = 0.66 milesTo convert our answer into feet, we con-

tinue a- follows:1 mile = 5,280 ft.

0.66 miles = 3,400 ft.

LENGTH OF SHADOWFigure 11-53

The altitude of the central peak ofAlphonsus is about 3,400 ft.

Students familiar with trigonometry maymake more accurate determinations by useof the tangent formula.

tan 11°

0.1944 CB3.2

CB .1944 x 3.2

= 0.62 miles

1 mile = 5,280 ft.

0.62 miles = 3,273 ft.

The altitude of the central peak ofAlphonsus is about 3,300 ft.

Using the above methods, astronomershave determined from both Ranger andEarth-based photographs craters up to about180 miles in diameter and mountainstowering over the surface of the moon morethan 25,000 ft.

Many new and striking ideas aboutthe Moon have resulted from the Ranger,and Surveyor rihotographs. There is stilla great deal more to learn from the_Ramer and -Surveyor photographs. In ract,c.-_,.*ntists will be studying these picturesfor years to come.

Figures 55, 56, 57, 58 and 59 are RangerIX photographs of the crater Alphonsus.You have seen that the scale changes withthe altitude of the satellite. It is necessaryto set up a series of scales to measuresurface features. The scales may be ap-proximated by a number of scale drawingsas represented by 1 igure 11-51.

Exercises:11. Measure the crater marked II in Figures

11-55, 56, 57. Determine its averagediameter.

Crater II

a. Figure 11-55b. Figure II-56c. Figure II-57

AverageScale Diameter

1" = 76 miles1" = 29 miles

_milesmiles

1" = 15 miles__miles

12. Determine an approximate diameterfor the crater marked III, Figures 55and 56.

Crater III

a. Figure II-55b. Figure 11-56

ScaleAverageDiameter

1" = 76 miles _ miles1" 29 miles _ miles

13. From Figure 11-59, determine the di-ameter of various crateis. Scale 1" =0.3 miles. Then, pick out the srmlleststructure visible to your eye, andcalculate its size in feet.

50

14. On the enclosed Atlas of the moon,Figure 11-60, locate and mark the im-pact point of the following moonsatellites. Remember that North isto the bottom of. the page, East to theleft, and West is to the right.a. Ranger VIIImpacted 7/13/64

Lat. 10°SLong. 20°W

b. Ranger VIIIImpacted 2/20/65Lat. 2° NLong. 2° E

c. Ranger IX-1mpacted 3/24/65Lat. 13° SLong. 2° W

d. Surveyor ISoftlanding 6/1/66Lat. 2° SLong. 4°W

e. Surveyor IIFailed, Impacted9/20/66Seathing Bay area, SEof Copernius

f. Surveyor IIISoftlanding 4/19/67Lat. 3°SLong. 23°W

g. Surveyor IVImpacted 7/16/67Lat. 0°NLong. 1°W

h. Surveyor VSoftlanding 9/10/67Lat. 1°NLong. 23°E

i. Surveyor VISoftlanding 11/9/67Lat. 0°NLong. 1°W

. Surveyor VIISoftlanding 1/10/68Lat. 40° SLong. 11°W

diviei

pt,141,1tp "

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Odit4616

141,1111

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_I.1..11171,141.

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59

56

Lunar MapThis map of the moon is based onthe original drawing by Karel Andel,published in 1926 as Mappa Seleno-graphica.

MOUNTAINS AND VALLEYSa. Alpine Valleyb. Alps Mts.c. Altai Mts.d. Apennine Mts.e. Carpathian Mts.f. Caucasus Mts.g. D'Alembert Mts.h. Doerfel Mts.i. Haenius Mts.j. Harbinger Mts.k. Heraclides Prom.1. Hyginus Cleft

m. Jura Mts.

n. Laplace Prom.o. Leibnitz Mts.p. Picoq. Pitonr. Pyrenees Mts.s. Rheita Valleyt. kiphaens Mts.u. Rook Mts.v. Spitzbergenw. Straight Rangex. Straight Wolly. Taurus Mr.z. TenerifTe

LUNAR CRATERS

1. .Abenezra2. Abulfeda3. Agatharcbides4. Agrippa5. Albategnius6. Alexander7."Aliacensis8. Almanon9. Alpetragius

la. Alphonsns11. Apianus12. Apollonius13. Arago14. Archimedes15. Archytas16. Aristarchus17. Aristillus18. Aristoteles19. Arzachel20. Asclepi21. Atlas22. Autolycus23. Azophi24. Baco25. Badly26. Barocitts27. Bayer28. Beaumont29. Bernouilli30. Berzelins31. Bessel32. Bettinus33, Bianchini34. Ric la35. Billy36. Birmingham37. Bin:38. Blancanus39. Blanchinus40. Boguslawcky41. Bohnenberger42. Bond, W. C.43. Bonpland44. Borda15. Boscovich46. 11..,,q!ter47. ::,:ussingar.

48. Bullialdus49. Bu:ckhardt50. Burg

51. Calippus52. Campanus53. Capella54. Capuanus55. Cardanus56. Casatus57. Cassini58. Catharina59.60.61,62.63.64.65.66.67.68.69.70.71.72.73.

1.

75.76.77.

79.80.81.p?.

84.85.86.37.38.89.90.91.92.

CavaleriusCavendishCelsiusCepheusChacornacCichusClairautClausiusClaviusCleomedesColomboCondamineCondorcetCononCookCopernicusCriigerCurtiusCuvierCyrillus

Damoisea LI

DaniellDavyDawes

GasparisDelambreDe la RueDelaunayDelisleDelucDescartesDiophantusDollondDoppelmayer

93. Eichstalt91. Encke95. Endyinion98. Epigenes97. Eratosthenes98. Euclides99. Eudoxus

100, Etiler

/01. Fabriciu.102. Faraday103. Fermat104. Fernelius105. Firmicus106. Flamsteed107. Fontenelle108. Fracastorius109. Fra Mauro110. Franklhi111. Furnenus

!12. Gambart113. Gassendi114. Gauricus115. Gauss116. Gay-Lussac117. Oeber118. Geminus119. Gemma Frisius120. Goclenius121. Godin122. Goodacre123. Grimaldi124. Gruithuisen125. Gi,ricke126. ,:nberg127. Hahn128. Hainzel129. Halley130. Hansteen131. Harpalus132. Hase133. Heinsius134. Helicon135. Hell136. Heraclitus137. Hercules138. Herigonius139. Herodotus140. Herschel141. Herschel, J.142. Hesiod us143. Hevelius 214.144. Hippalus 215.145. Hipparchus 216.146. Horrebow 217.147. Horrocks 218.148 Hortansius 219.149. tlumboldt, W. 220.150. Hypatia 221.

151. Isidorus 222.223.

11523: Jaansen 224.225.

154: Julius Caesar 226.227.155. Kepler

156. Kies 228.

157. Kirch 229,230.158. Klaproth 231.159. Klein

160. Krafft 232.233.

161. Landsberg C 234.162. Lagrange 255.163. Lalande 236.

164. Lambert165. Landsberg166. Langrenus167. Lassell168. Lee169. Lehmann170. Letronne171. Levzrrier172. Lexell173. Licetus174. Lilius175, Lindenan176. Linne177. Littrow178. Lohrmann179. Lon5ontontanus180. Lubiniezky181. Maclear182. Macrobi us183. Mddler184. Magelhaens185. Maginus186. Mairan187. Manilius118d. Manzinus189. Maraldi190. Marinus191. Maskelyne192. Maupertuis193. Maurolycus194. Mayer, Tobias195. MenelausI 96. Mercator197. Mcrsenius198. Messala199. Messier200. Metius201. Melon202. Milichius203, Miller201. Monge295, Moretus206. M6sting207, Mutus208. Nasireddin209. Neander210. Nearchus211. Nicolai

212. Oken213. Oron tius

60

PalisaPallasParrotParryPeircePetaviusPhilolausPhocylidesPiazziPicardPiccolominiPickering, W. H.PictetPitatusPitiscusPlanaPlatoPlayfairPliniusPontanttsPontecotdantPosidoninsPrinz

237.238.239.240.241.242.

243.244.245.246.247.248.

250.251.252.253.251.255.

256.257.258.259.260.261.262.263.264.265.266.267.268.269.270.271.272.273.274.

275.276.277.278.279.280.281.282.283.284.

ProclusProtagorasPtolemaeusPurbachPythagorasPytheasRabbi LeviRamsdenRegiomontanusRetchenbachReinerReinholdRepsoldkhaeticuskheitaRiccioliMinerRossRothmaiiiiSacroboscoSan thenSasseridesSaussureScheinerSchickardSch illerSchröterSeieuctisSharpSimpeliusSnelliusSosigenesStailiusStevin usStilflerStraboStruveStruve, OttoTacitusTaruntinsTheaetetusThebitTheophilusTimaeusTimocharisTorricelliTriesneckerTycho

285. Men.VendelinusVietaVitelloVitruviusVlacq

WalterWeissWernerWilhelm IWilkinsWurzelbauer

286.287.288.289.290.

291.292.293.294.295.296.

297.298.299.300.

ZachZagutZuchiusZupus

"(X

)

Answers to Chapter II

1.a. The standard number of drops perminute is found by dividing the totalnumber of drops by the number ofminutes, in this case, 5.

Standard60

StandardStandard x 60 orStandard x 60

1,000Standard x 60 x 24

1,000Standard x 60 x 24 x 365

1,000Standard x 60 x 24 x 365

(4)

(5)

or 1,000 x 1,000c. (1) 1,000 x 1,000 = 1,000,000

= 1 x 106 = 1 million

2. Standard x 90

3.a. Standard x 25b. Standard x 25

22

4. Some problems encountered whenusing drop time are as follows:All drops are not the same size.The number of drops per minutewould vary depending upon how fullthe cup is. Try this.As the opening became larger aftercontinued use, the water would dropout faster..You have to keep filling the cup.

e. In cold weather, the water couldfreeze, and in high temperatures, thewater could boil.

As early as 1400 BC., the Egyptiansconstructed water clocks and they wereused almost 2,000 years as time-keepers.

5.a. Complete as instructed.b. (1) about 4:45 PM

(2) about 7: I PM(3) about 2:15 AM(4) about 8:45 AM

c. (1)(2)(3)(4)(5)(6)

d. (1)(2)(3)(4)(5)

5.e.

6:00 PM6 hoursabout 10:45 PMabout 1:15 PMabout 8:15 AMabout 2:45 PM6 hours6 hours6 hours6 hours6 hours

Time

New YorkGreenwich aboutMoscow aboutTokyo aboutLos Angeles about6.a.

b.C.d.e.f.g.h.i.j.

k.

7. a.b.C.d.C.f.g.h.1.

J.

Angle ofthe Sun

6:00 AM 18 hours10:45 AM 22 hours 45'

1:15 AM 1 hour 15'8:15 PM 8 hour 15'2:45 AM 14 hour 45'

6:00 AM6:00 AM oy sunrise12 midnightYes, it is dark when it rises12 noonNo, it is daylight when it sets12 hours6 nours12 midnight to 6:00 AMNo, the waning third quarter does notrise until midnight.(1) Midnight(2) Noon(3) 12(4) 6 hours, from Midnight to 6:00

AM

600 AMSoutheast3:00 AMYes, it is still dark at 3:00 AM9:00 AM3:00 PMNo, it is still light at 3:00 PM12 hours3 houis(1) 3:00 AM(2) 3:00 PM(3) 12 hours(4) 3 hours, from 3:00 AM until 6:00

AM

8.a. ( 1 ) Full MoonMidn4ht

(2) 1st Quarter9:00 PM

(3) Waxing Gibbous9:00 PM

b. (1) Waning Crescent6: 00 AMSoutheast

(2) Waxing Crescent6:00 PMSouthwest

9.a. Apogeeb. Perigeec. Average

Distance 898.5 milesd. Eccentricity 0.14

1.573 miles224 miles

10.a. Apogee 1.740 milesb. Perigee 118 milesc. Average

Distance 929 milesd. Eccentricity 0.17

11. Average Diametera. about 24.5 milesb. about 25 milesc. about 24.5 miles

12. Average Diametera. about 52 milesb. about 51 miles

13. Smallest features visible in Figure 61are about 500 feet.

14. Add other satellites and landings, to themap of the moon as they occur. Youcan obtain their position from yourlocal newspaper.

NOTE: In the printing process the above instru-meats may have become somewhat inaccurate, there-fore you may wish to use your own plastic, metalor wood instruments.

tf)

to

(I)

tr)

te)

cz

"EMPTY" SPACE

How is IL possible to describe the measureof "empty" space which contains onlyabout 1 particle of material per cubicmile? The content of "empty" space con-tains a wind that travels faster than thespeed of sound, strong enough to producethe tail of a comet, a wind which cannot beseen but can be measured (Figure 111-2 and11I-3). These are the solar winds hightemperature electrified gases from the sur-face of the sun. Also throughout spacethere are fields of gravity, electricity, andmagnetism which can be used to describeits measure.

Figure 111-2

Radiation beltstrap solar wind particles

Orbit ofIMP satellite

one4..::f : turbulence

--.7t....,==""? ..vcc

Moon's waKe detected'December 15, 1963 ,

-17

*11Z,,i:NP.rtg0 4 --,..n"V.4t-9W4V:e:POt\-,pa+-...-......--......-----...._'.*4*...74;i' ,`,:,&.,, ,' cF4A 4. 1

,,o.4.,,_ ............_..,_0;,,,.4,..eA , , ..,,,v-..,-.. "...l'rzie47,:s-P W---"P't",).,,- 4,114f .,;0043. -:-Wkw,,,,-,,..4:S:,,,1,111 ..y,.:Alg'i -:

Figure 111-3

64/69

. 14

11 . * * II

0

o

411. tti .

II k I .

I .I

s . o s . I . 1.1 . I .

. I IS I

: I 1_ 0 I Ii 1 s

6 I :.4 I I is 1-6

I . I I

I 11 4 di 0 I " 11 . I

I . s . 11. I I I I I

.e / I . I II

4 1 t !-1_ I 1 . 1

I . . 5 i I 15 0 . , I

I I 4 0 0A II I

. 14 I 0 I. a

s I I ID 0 I

0 . .

II IIl

o

Figure 111-6

moves back and forth 256 times. This re-sults in 256 compressions and rarefactions(sound waves) being sent out into the airevery second.

When your ear hears the piano note,your ear drum also vibrates 256 times asecond. At any point within the range ofthis sound, 256 sound waves go past everysecond. If we know how far it is from onewave to the next, we can soon computehow fast the waves are traveling. This isoften compared to a railroad train- passinga crossing. If twenty cars go past in a minuteand each car is fifty feet long, then 20 carsper minute x 50 feet per car equals 1000feet per minute which is the velocity of

4,1,1Y/4. 4461w:4i kl*`/aglii4414140#

:11

the train. With sound waves the statementis "velocity equals number of vibrationsper second (frequency) times distance fromone wave to next (wavelength), orv f x 2.

Now to measure the length of asound wave. Imagine a wave likethis and a- second waveidentical to the firstBut suppose the second wave travels just awave length behind the first:

What wave will result if they are addedtogether? The "hills" of one wave areadded to the "valleys" of the other wave,and the result could be represented iikethis . These waves cancelled eachother when they were added together.

Now imagine the two waves are travelingexactly together:

This wave will result if they are addedtogether:

It will result in a wave with the same fre-quency but higher hills and deeper valleysa stronger wave or a louder sound.

If two sound waves cancel each othersilence results. If two sound wavesstrengthen or re-enforce one another, amuch louder sound results. The effect ofsound waves re-enforcing one another iscalled resonance.

Figure 111-7

fr

71

Figure 111-8

We can use resonance to help us measurethe length of a sound wave. We will need agraduated cylinder of at least 100 millilitercapacity, a tuning fork with a frequency of700 cycles per second or higher, a metricruler, and a small amount of water.

If the vibrating tuning -fork is held overthe open end of the cylinder, Figure 111-8,the compressions and rarefactions traveldown tc the closed end of the cylinder, arereflected from the bottom of the cylinder,and travel back out the open end of thecylinder. A louder sound, or resonance,will occur if the cylinder is just the rightlength so that a compression and rare-faction travel down it, reflect and arriveback at the open end while the tuningfork' is completing one-half of its vibration.During the other half-vibration, a compres-sion and rarefaction are produced in theopposite direction, and add to the com-pression and rarefaction emerging from thecylinder to make the sound louder.

In other words, resonance will occur ifthe length of the cylinder is exactly one-fourth the length of the sound wave.Resonance can also occur if the length ofthe cylinder is three-fourths of a wavelength, or one and one-fourth wave length,or one and three-fourths wave length, etc.Can you decide why the cylinder cannot beone-half wave length or one wave lengthlong for resonance to occur?

72

Hold the vibrating fork over the openend of the cylinder. If resonance does notoccur with an empty cylinder, slowly, veryslowly, add water to the cylinder until thevolume of sound increases sharply. Whenresonance occurs, measure the distancefrom the top of the cylinder to the surfaceof the water.

Continue to add water slowly to thecylinder while the vibrating fork is heldover the top. If resonance occurs again,measure the distance from the top to thesurface of the water. The difference be-tween these two measurements is one-halfwave length.

If resonance does not occur again withthis cylinder, then the distance from thetop to the surface of the water representsone-fourth of a wave length, and should bemultiplied by four to give the wave length.

Once the wave length has been measured,and with the frequency of the tuning forkknown, the speed of sound can be calcu-lated from v f X P. You should be able tomeasure the speed of sound to be about335 meters per second.

If you discover errors in your measure-ment, perhaps you can think of ways ofimproving your techniques. Does thediameter of the cylinder have any effecton wave length? The longer the wavelength you use, the smaller will be yourerror of measure, Do you think dif-ferences m temperature or pressure of theair could cause errors of measurement?

The speed of sound is dependent uponair temperature. Can sound be used tomeasure temperature in the upper atmos-phere? When rockets became availablefor scientific use, methods for measuringtemperature with sound were devised. Onetechnique has proved very valuable.

As the rocket soars upward, specialgrenades are ejected from it one aftern.nother. so they explode with bright flashesand loud noises, Figure 111-9.

Ground based radar tracking stationand special photographic trackers are usedto pinpoint the location of each explosion.Meanwhile, sensitive microphones are usedto detect the sounds of the explosions whenthey arrive at the ground, and differencesbetween arrival times are computed andrecorded electronically.

90-4, 1?-312KILOMETERS

5045

40

/G3

G2

G1

SOUNDRECORDING

BALLISTICCAMERA

DOPPLEREFFECT

TRACKER

Schematic diagram of the grenade-experiment system. Radar, ballistic camera,and Doppler tracking systems are indicated.Each individual system or combination ofsystems suffices for the experiment. Soundrecording site is preferably located directlyunder the rocket trajectory. G1 , G2, G3,and G12 indicate various altitudes of gre-nade explosions.

Figure 111-9

Using the relationship that Velocityequals Distance divided by Time (V =D/T), distance being the difference inaltitude between successive explosions, andtime, the interval between recorded sounds,the velocity of sound within tl.k.) altitudeinterval can be computed.

We have all heard the "beep-boop-beep"of Vanguard I, one of America's first satel-lites, Figure III-10.

73

The tones are the voice of the satelliteWhat do these tones from space mean?What is the satellite "saying?" Whatlanguages does the satellite use? Thesatellites transmit their information backto earth by transmitting a special kind ofnumber called a binary number. We areall familiar with numbers which containthe numerals 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9.A binary number contains only 1 and 0 yetcan be used to represent any number ofitems.

The binary system is based on 2's insteadof 10's like our ordinary numeration sys-tem. Here is a 7 place binary ilumeral1 1 1 1 1 1 1. It means: 1(64) +1(32) + 1(16) + 1(8) + 1(4) + 1(2) +1(1) = 127. Each place in a binarynumeral contains a digit which is twice thevalue of the diet in (he previous place. Ina binary numeral a (I) is used to indicatethat the place is filled and a (0) is used toindicate that it is not. Binary numerals are

IX se Eli 1 ID e catise any -value can be writtenusing only two different digits, (1 arid 0).'Thus the 7 digit binary numeral 1010101means: 1(64) -I- 0(.3 23 -1- 1 (1 6) 1- 0(8) -I-1 (4-) -1- 0(2) 1(1) = 8 5_ Flow vv....11.11c1' you.write the binary- numeral for 36? (Answer:100100 = 1(3 2) -I- 0(16) 1- 0(8) 1- 1(4-) 1-0( 2) 1- 0(1 ) = 36_ Space -vehicles utilize thebinary number system which. can representany quantity. Can you write a binary nu-meral for e1i of these: 0, 1, 2, 3, 4, 5, 6,7, 8, 9?

_Answer:0 = 0(1) = 01 =--- 1(1) = 110 = 1(2) -4- 0 (1 ) = 2

1 1 = 1(2) 1- 1(1 ) = 3100 = 1(4-) -1- 0(2) 0(1) == 4-101 = 1(4-) 1- 0(2) -i- 1(1) = 51 10 = 1(4-) -F 1(2) -1- 0(1) = 61 1 1 = 1(4-) -1- 1(2) 1 (1) = 71000 = 1(8) 1- 0(4-) -I- 0(2) 0(1) = 81001 --= 1(8) -1- 0(4-) -1- 0(2) -I- 1(1) = 9

A. satellite ccnild send back infox-rnatiori inthe binary system in any way that wasneeded:.A. satellite may transmit any number bytransmitting back only two airfeterit rtrusi-al notes or tones_ A. high note could iiriai-cate the digit (1) and a low note tne digit(o). Beep, Beep, Boop could stand for thebinary numeral 1 1 0 which means 1(4)1 2 0(1 ) or 4 2 0 = 6. 'This aouldrepresent si.,c things or be the digit 6 in abase ten numeral- Flow could yoii send theeligits 5 and 6 representing 56 with bepsarid &coops? Think up others_When Mariner IV passed by Mars it sentpictures of the Martian. landscape -usinglainary numbers.. Mariner. 1V's camera sawthe Martian landscape in 'terms of dif-ferent light intensities_ _The electronicequipment onboard the spacecraft inter-preted -various light inteyisities as differentnumbers and them transmitted each. numberback to Earth. On Earth each number wastranslated back to a light intensity and thepicture of Mars was constructed_ FigureIII-1 1_

)1

, ....4 4 ,.,,..,6 ,,.....1,4

...1 ,,,.

10.600146,,,Oliabillthitopoew

AI *11,400,006,01,1 04,,,o0.4,61iiii0A

0,14004,4,1014.,61,i..., ,, oil f0., i'' 0M

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1)

MOSAIC OF TIROS PHOTO9RAPHS

SI

+41111.--

°P000.11 L

-4

1011

10

90,Itcx

WEATHER MAP, MAY 20, 1960, WITH TIROS CLOUD DATA

Figure 111-1 2

Satel helped to- develop models of the world's weather. Before 1960,

weather ...ns were limited, and weather Tiaps contained vast blank regions over

oceans, deserts, and other sparsely populated areas.Since April 1, 1960, NASA TIROS (Television Infra Red Observation Satellite) Weather

satellites have enabled meteorologists to obtain photographs of large areas of Earth andtherefore to deal with weather on a hemispheric or even global basis.

TIROS photographs look much like the cloud cover over Earth, but must be transferred

to charts to produce a geometric model for detailed weather analyr,is.Figure 111-12 shows how TIROS I made history by yielding data which related cloud

patterns to weather. The top photograph in Figure III-12 is a mosaic of TIROS photographs

covering about one-fourth of Earth's surface. The lower picture is of a weather map based

on the mosaic.From this weather map, meteorologists are able to identify and locate areas of low pres-

sure, L, indicating cloud cover and possibly precipitation, or high pressure areas, H, with

clear skies and fair weather. He is also able to locate weather fronts, ahAILA4&. , cold

fronts and, ilebtailhath , warm fronts. From the position of tlie front, he is able to esti-

mate when the weather will change at a given location.

.69

Figure III-1 3

=MI

To obtain more complete coverage ofEarth, TIROS IX, Figure 111-13, waslaunched Jantr-4 22, 1965. The ninth inthe TIROS series was the first satellite tophotograph the entire sunlit portion ofEarth on a daily basis.

Early TIROS satellites were placed inan east-west orbit and were able to photo-graph only 25% of Earth's cloud cover perday. TIROS IX was launched into a north-south orbit, Figure 111-1 4, and was able toprovide total coverage due to the relation-ship of the satellite's movement and Earth'srotation. As the satellite orbits north-south, Earth rotates east-west under it.Also, TIROS IX was placed in almost a sun-synchronous orbit. That is to say, thenormal westward drift of the orbit is thesame as Earth's motion around the sun.This placed the sun continuously oppositeEarth and provided for constant and favor-able lighting for the photographing ofEarth, Figure 111-15.

76

.41STANDARD TIROS

/ORIENTATTN

6TH ORBIT

s

10T14 ORBIT = ,

IBTH ORBIT

WHEEL ORIENTATION\

Figure 111-14

Another factor in the improved cover-age by TIROS IX was the position of its TVcameras. Earlier TIROS satellites hadcameras on the base of the drum-shapedspacecraft. At times, when the base wasturned away from Earth, the cameras lookedinto space. TIROS IX's cameras weremounted on opposite sides of the drum.As the satene slowly "cartwheeled"through space, the cameras photographedEarth as it came into view, Figure 111-13.

ORBIT PLANEPRECESSES EASTERLYAPPROX 10 PER DAY

WINTERSOLSTICE

VERNALEQUINOX

0

AUTUMNEQUINOX

1,,SUN

707/ \

SUMMERSOLStICE

Figure 111-15

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51i . -- , NOWFigure II1-1 6

From analysis of early weather models,meteorologists realized that accurate pre-diction and understanding of weather dy-namics could only result from more com-plete observations of greater areas of theglobe which would have to be taken fromgreater altitudes above Earth- The twomajor techniques used to provide this in-formation are sounding rockets, Figure III-1 6, and the TIROS, TOS, Nimbus, andESSA meteorological satellite programs.(The ESSA satellites of the EnvironmentalScience Services Administration of theDepartment of Commerce utilize TIROStechnology on an operational basis.)

Construction of meteorological modelsand weather charts requires mathematicaldata on cloud cover, atmospheric pressure,winds at various altitudes, temperature, andmoisture.

These data can be secured by radiosondestations which send .balloons aloft severaltimes daily. Each balloon carries equipmentto provide data on atmospheric wind,pressure, temperature, and moisture. Thisballoon technique secures a vertical sampl-ing of the atmosphere up to about thirtykilometers (1 8 miles) above the surface,Figure III- 1 7.

As far as eximathematicalradiosonde olgeographical ii

Eventuallyfined, but noservations anments are p.materials, equ_niques are tknowledge of

1

THE MEASURE OF OUR ATMOSPHERE

"Explorer Flight Successful" -So read theheadlines in November 1935, referring tothe then amazing flight in which two men,sealed in a metal gondola, flew a balloon tothe astounding altitude of 72,395 feet(about 22 kilometers) and returned safelyto Earth. In January, 1958, another"Explorer" flew succeisfully, this time 10orbit Earth, at altitudes exceeding 1000miles (over 1,600 kilometers). The missionof both "Explorers" included "scientificexploration of the upper atmosphere."Man's idea of "the upper atmosphere"changed in those 23 short years. Thischapter illustrates how scientists have de-veloped ways to measure a now very nearand important part of space the atmos-phere.

Until the development of powerful rock-ets during World War II, almost all researchof the upper atmosphere (Figure IV-2) waslimited to observations which could bemade from the ground or by instrumentscarried by balloons. Instruments carried

5UJ

400

300

200

EXOSPHERE

250

- 200

MIDDLEATMOSPHERE-

30 STRATOSPHERE1 0 _TROPOSPHERE 6

Figure IV-2

aloft by these balloons could seldom achievealtitudes greater than about 30 kilometers(18 miles). Sounding rockets have beendeveloped to help fill this void between the_instrument carrying balloons and the orbit-ing satellites, Frgure -Tlie soundingrockets have been immensely valuable incollecting information about our upperatmosphere. The sounding rockets are simi-lar to those vehicles used in the explorationof space, but are usually smaller. Theiraltitude is limited so they do not departfrom the environment of Earth which theyare designed to explore.

The Earth and its atmosphere, FigureIV-4, can be thought,of as a "system." AtEarth's surface, gases and other materialsare leaving the atmosphere to become partof solid Earth. WIlat do you think hap-pens to the materials which enter thelower atmosphere from Earth? Some Willwork their way into the upper atmosphere,and some substances in the upper atmos-phere will move down into lower layers.Considerable "trading" has occurred be-tween the parts of the Earth-atmospheresystem.

But what happens at the outer bounda--ries of the atmosphere? More tradingoccurs. Substances which once were partof solid Earth leave. New materials arecaptured from space to one day becomepart of solid Earth, Figure IV-5. Studyingthe way these "trades" are being made(and have been made from Earth's be-1.nning) could provide information aboutEarth both now and at the time of itsformation.

In order to better, understand Earthtoday, we need to know when, where, andto what extent changes and events aretaking place in the upper atmosphere. Todo so requires the ability to 1.r...,ate and de-scribe phenomena as they occur.

The concept of a "system" is importantin science. Select a group of objects atrandom. Devise a system in which eachobject is an integral part of an operatingsystem. For example a ruler, a protractor,an art gum eraser, and a pencil could bemade into a "teeter-totter" lysterif, (FigureIV-6). A glass, some water and a corkstopper could produce another; pieces of

wire, a socket, a dry cell, a switch, and acell holder would be another. When thevarious parts act together, we have a sys-tem. In a system, changes in one part, pro-duce changes throughout the system.

Not all scientists carrying out researchof the upper atmosphere are interested inthe same phenomena. Each experimenterrequires specific data, such as obtainedfrom a particular altitude, or c cidingwith special events taking place on sun,or tlined with passages of a satellite over-head, Figure IV-7.

Meteorologists ask: "What factors pres-ent in the upper atmosphere affect theweather?" In the troposphere, the lowestlayer of atmosphere where nearly allweather is "made,' changes in temperatureand pressure, wind speed and direction,humidity, precipitation and cloud coveraffect the system whic,(i we call our weather.

In addition to reporting present weatherconditions, the purpose of the measure-ments is to note any trends or patternsthat seem to be developing. When a patternin the Earth-atmosphi-:Te system is de-tected, it is possible to make certain pre-dictions as to what the weather is likelyto be in the near future.

To make these predictions, we mustrely upon the fact that the tropi. Thereconsists of gases which are free to . OW ormove within the system under com-bined effect of all forces acting tux, them.Upper layers of the atmosphere cc, nsiq ofgases which rest upon the lower '!ayers.Changes taking place in the upper h. 3rs ofthe atmosphere may result in various 1;.rcesbeing exerted upon lower layers.

The upper atmosphere is, therefore,studied because of its unique position withrespect to space. We need to know what

KM

500

400

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ULTRA V!OL ET MEAN FREEPRESSURE PATH

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Figure IV-4

1

ATMOSPHERE

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Figure IV-5

Figurg

83

COSMIC R,1.YSMETEORS

Ef 0:N DARY

1500

50

effects are produced by phenomena suchas incoming solar radiation, solar wind,meteors and cosmic rays. These data mayprovide evidence related to phenomenasuch as aurnra lair storms, and night

s of upper atmos-phere are subjected to many external andinternal forces. They react to these forcesaccordingly.

The nature and behavüor of gases nearthe surface of Earth las occupied theattention of a large nimplicr of scientistsfor a great many years. :Won recently, thenecessity of understandimg the behavior ofgases and fluids at -The altitudes hasoccupied the attentionmf Race scientists.On July 17, 1929, Dr. Robert 11. Goddardwas the first investigator to successfullylaunch a, scientific pay1ow3 This first pay-load consisted of a barcarater, a thermom-eter and a camera. Figue IV-8 shows Dr.Goddanl, second from-le right, with col-leaves holding the rocl= used in the flightof April 19, 1932.

At any given time., a reasonable de-scription of the state Jok- a gas is providedby measuring three q-quantities; density,

Atomic hydrogen Weathersatel I ites

400

Atomic oxygen

Electron density(electron/cm )

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Compositionchemioe,I reactions

Atmospheric oh enomenaand c-bservational tools

Figure IV-8

temperature, and pressure. Difficulties inmeasuring the volume of the atmospheresurrounding Earth are apparent. Sincedensity is closely related to volume, themeasurement of density can be substitutedas an indirect method in the measurementof volume.

What shall we measure? We must learnto measure (1) density, (2) temperature,and (3) pressure.

You have probably made many atmos-pheric measurements such as presscre,temperature, cloud formations, precipiia-tion, etc. The data that you have collectedis similar to information obtained fromscientific upper atmosphere measurements.

Try this: During a one week period makea number of different measurements in re-lation to Earth's atmosphere. Select specifictimes to make your' measurements severalhours apart three or four times each day.Develop charts, graphs, tables, etc. torecord your observations. How many dif-ferent kinds of data can you gather? (Youwill need a physics text and one for geom-etry and to know how to use the index.)Include some of the following in additionto others you may devise.

a. Make a mercurial barometer. Recorda tmospheric pressure readings in millimetersof mercury.

b. Record air temperatures in differentlocations around your home and school.Select open, paved, grassy, shady, or, woodareas. Use a centigrade scale thermometer.

c. Use an anemometer to record windspeeds. Record data in kilometers per hour.Make measurements in different locations..

d. Record vane revolutions per minute ofa Crookes radiometer placed in different lo-cations. Devise filter systems for use whenrevolutions are too rapid to count.

e. Take measurements with a light meterand record values in foot candles. Use asolar cell with a voltmeter and record valuesin millivolts. Compare results.

f. Use a geiger counter and record back-ground "noise."

g. Devise methods of determining cloudheight, speed, and cloud types.

h. Launch, helium balloons. Recorddirection, speed, rate of ascent and altitudewhen last visible.

i. Use a radio to determine long-distanceradio reception. Compare broadcast, long

85

77

wave and short wave, bands. Use maps ora globe to show station locations anddistances in kilometers. List station fre-quency in kilocycles or megacycles persecond.

j. Determine what gaseous and solidparticles are added to the atmosphere byautomobile, industry, homes, etc. in yourown community.

k. Develop means of determining visi-bility distance.

1. Use a simple method, sucn as thatshown in Figure IV-9, to estimate airturbulence.

Volume is the term used to describe anenclosed space. Stated in another way,volume is the measure of the amount ofspace enclosed within defined boundaries.Volume has three dimensions, length, widthand depth or height. Units used to expressvolume are called "cubic units," such ascubic inches or cubic centimeters. Thedevelopment of the measurement of volumefrom units of length is an intriguing story,and may provide some interesting readingfor you.

Measuring volumes of gases at the surfaceof Earth is practical, for a gas may be en-closed within containers of fixed dimen-sions. Measuring volumes of gases high inthe atmosphere presents new problems.Gases in the atmosphere are not enclosedwithin containers, and the atmosphere itselfmay not have measurable boundaries. Fig-ures IV-10 and IV-11 illustrate some of thedifficulties of placing a package of measure-ment instruments into orbit. Figure IV-11shows Explorer XIX fully inflated whereasFigure IV-10 shows the same satellitepacked into its canister and extendingoutward from the fourth stage of a Scoutlaunch vehicle.

One way to solve this problem is toobtain samples of gases from the atmos-phere. When samples are collected however,the volumes of the samples are prede-termined by the sizes of containers usedfor collection. Consequently, if all sampleshave identical volumes, some other unit ofmeasurement must be used to comparethem.

A common method for comparing onesample with another is to measure theamount of material in each. The amount

86

Figure IV-9

^

of material present in a substance is calledits mass, not its weight.

Weight is often defined as the force ofattraction which exists between a mass andEarth. Mass remains the same for anyplace. Your mass, your number of atoms,will be the same on the moon as on Earth.However, since the moon's gravity is lessthan that of Earth, your moon weightwould be less than your Earth weight.Your weight on Earth will also vary at dif-ferent Earth loca..ions: the Equator, at the

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Poles, in a deep mine, on a mountain top,etc_ To change the mass of an object itwould be necessary tc, alter the number ofatoms it containt;. As the Aerobee rocketsuccessfully lifts off to the atmosphere,(Figure IV-12) its weight changes as thedistance from Earth increases and bothweight and mass are decreasing as rocketfuel is consumed.

Suppose a sample of air is obtained fromthe troposphere, and the mass of thissample is measured as 6 grams. With asounding rocket, a sample of air with equalvolume is recovered from the upper atmos-phere_ The mass of this sample is measuredas I gram. Which of the following state-ments would be a better conclusion to drawfrom this evidence?

a. The mass of the air in the upperatmosphere is less than the mass -ofair in the troposphere_

b. Volume for volume, the mass of theair in the upper atmosphere is lessthan the mass of air in the troposphere.

Only masses of small volumes of air weremeasured, not masses of the entire atmos-phere, but the volumes were equal. Onwhat basis could masses of samples be com-pared if volumes were not equal? This is aquestion of some practical importance_Measuring instruments carried as payloadon rockets are limited by the size and shapeof the rocket itself_

Masses of samples can be compared onlyif the mass of each sample is related to itsvolume. To illustrate, suppose that onesample of air recovered has a volume equalto 870 ml. (milliliters) and a mass equal to27 grams_What would be the mass of 1 ml. of thissample? What would be the mass of 1 ml_of a sample with volume equal to 860 ml.and mass equal to 25 grams? To find theseanswers it is necessary for you to divide themeasure of mass by the measure of volume-for each sample_ As a result of this division,the samples are described as having a certainmeasure of mass for each unit of volume.This is the concept of density.Scientists would define density as "themass per unit of volume." Mathematicianswould define it as. D = WV, which is readas: -density equals mass divided byvolume." 'You will also notice that density

pipt.tei+4

1

I

varies directly with mass and inversely withvolume. The principle is the same. Densityis calculated by dividing the measure ofmass by the measure of volume.

When density is stated, units of measuremust always be included. Thus, the densityof the first sample of air would be statedas 0.031 g/m1., read as "zero point zerothree one grams per milliliter" or 31thousandths grams per milliliter." Themass of the second sample would bestated as 0.029 g/ml., read as "zero pointzero two nine grams per milliliter, or"29 thousandths grams per milliliter."

Do you think these two samples of aircould have been obtained from the sameplace at the same time? Give your reasons.If the second sample was obtained from ahigher altitude than the first sample, whatmight you hypothesize about the nature ofthe atmosphere? Remember density de-creases as altitude increases.

Defining our problem ab out the atmos-phere in another way, we say "density is ameasure of the amount of material presentwithin a given space at a given time. ' Dueto this fact we consider both volume anddenSity to describe samples from the upperatmosphere. With this in mind, imaginethat you are riding at a speed of 20 kilom-eters per hour in a motor boat, and youstick your hand up into the air. Imaginethe push of air on your hand. Now imaginethat you cautiously place your hand intothe water alongside the boat as it continuesto move at 20 kilometers per hour, (FigureIV-13). Compare the push on your handmade by water with the push made by air.

Next imagine that you are an astronautin a spacecraft orbiting around the earthat 17,500 mph. As you prepare to leaveyour spacecraft to take a "walk in space,"you open the hatch and cautiously raiseyour hand (Figure IV-14). Imagine theforce you would feel on your hand andcompare it with the force from the waterand air. Which would you expect to bemost dense: Water, air or "empty" space?Least dense? Give your reasons.

Answers to these questions can be madeon the basis of the amount of push or forceagainst your, hand due to resistance offeredby substances through which your hand ismoving. The greater the density of thematerial, the greater the resistance; or the

g-

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Fture IV-13

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Figure IV-14

greater the resistance, the greater the densityof the material.

With your hand you made a crudemeasurement of the density of air andwater. Your m6asurement was only to de-termine which was greater or which wasless. How can we refine this methodof measuring so that it will provide accurateinformation about atmospheric density?

One group of scientists worked out thefollowing system. Imagine a light hollowsphere being released from a sounding rocketat the very top of its trajectory, Figure IV-15. As the sphere falls back to Earth, it mustpass through the atmosphere. Since thefalling object is spherical, resistance of theatmosphere will always be directed against

RUBBER BANDS

SLING SHOT

OUTEA CYLINDER

BLASI= r-IP alL4

INSTRUPIENTT CnMPAIRITMENT

Figure IV-I5

NOSE CONE

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SPHERE

,*

Figure IV-16

experiments above 30 kilometers. Spacescientists determine atmospheric density bythis method.

Figures IV-17 and IV-18 are graphsshowing the results of one such experi-ment. Figure IV-17 shows the radar plotsof altitude and the computed rate ofdescent for each altitude. Figure IV-18gives atmospheric density calculated foreach rate of descent of the sphere.

Use these two graphs as sources of in-formation to build a new graph as inFigure IV-19, showing the density of theatmosphere compared to altitude. Forexample, at 40 km the rate of descent is40 mi/sec from Figure IV-17, and a rate ofdescent of 40 m/sec indicates a density of4.0 pn/m3 from Figure IV-18. So onFigure IV-19, at altitude 40 km, plotdensity as 4.0 gm/m3 . Secures graph paperas in Figure IV-19 and continue to plot theother values and then connect your plottedpoints with a smoothly curved Erie.

The completed graph wir show thedensity of the atmosphere as it was meas-ured to be on a particular day. Many suchmeasurements must be made from a numberof different locations before a completepicture of the density of the atmospherecan be well known.

Use the graph you have constructed.Figure IV-19 to determine the density ofthe atmosphere at an altitude of 50 km.;55 km.; 65 km.

90

85

80

an equal amount of surface area. The rate 75

at which the sphere falls depends upon the 70

resistance of the air it is falling through. 2, L

The amount of resistance depend§ upon = "density of the air. t3' 60

Therefore, the rate of descent can beused to indirectly measure air density at 50

various altitudes. Radar measurements pro- <45vide continuous information about the rate

at which the sphere is descending. Addi-tional data from this method include thesideward motion of the sphere during thefree fall which in turn provides informationconcerning wind speed and direction in theupper levels of the atmosphere. FigureIV-16 illustrates a type of sphere used for

40

60 100 140 180 220

RATE OF DESCENT M/sec

Figure IV-17

260

8 .0

7.57.06 .5

6 .0

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40 80 120 160 200 240

RATE OF DESCENT MbecFigure IV-18

MINIM 11111111111111111111IIIIIMMI11111111111111111111111111111111111111111111111111111101111111111111111111111111111111111111111111111111111111111111111111I111111111111111=1111111IHNI1111111111111111111=111111111I

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0 10 20 30 40 50 60 70 80

ALTITUDE IN KM

Figure IV-19

You should find 1.1 gm/rn3, 0.60 gm/rnand 0.21 gm/re .

Imagine you are a scientist working on aproject concerned with the study of theatmosphere of Mars, and entrusted withdesigning an experiment to measure densityof the Martian atmosphere. From what youknow about the Martian atmosphere, whatchanges or modification in the sphere dropmetiod of measuring density might you

investigate? How would the lack of groundstations for radar; telemetry; allowancesfor probable mass of Mars; and unknownMartian winds influence your thinking?Remember all you have learned about themeasurement of gases.

The density of a gas is influenced bytemperature. Temperature is somethingall of us have learned about intuitively inmuch the same way we have learned aboutt Aghtness of light, shadings of color, loud-nem f sound, or smoothness of texture.Altheigh we can "feel" temperature, we;need o kncot- about its measure.

If ,mked to describe what is meant_ bytreammaturc, a common answer is, "rain-pera.L1we is tow hot or how cold somethingis." Uhis innnlies that an entire range oftemp,-ratures must exist. Cool, warm, icy,5aripor, lukewarm, balmy, hot, Or cold arebiat Ai few wards used to express tempera-tuses "These words are descriptive - theydescfite how the temperature of an object"eeis." A temperature value could beassigned to =reach term. Using the properterm, it is possible to communicate tosomeone else the description or value ofthe temperature which a certain objectpossesses.

Use Figure IV-20 to develop a scale ofdescriptive terms. AA others you know toprepare similar lists. Compare lists. Par-ticularly notice words used within specifictemperature ranges. If others are asked todescribe or place a value on this sametemperature, a major weakness of the scalebecomes apparent. A descriptive scale issubjective - a pers6nal estimate of judg-ment or opinion is required by each personusing it. Prove this subjectiveness to your-self very quickly. Listen to the commentsof your classmates as they describe thetemperature of outer space, or the surfaceof the sun, ,or the heat shield of a space-craft as it re-enters.the atmosphere, FigureIV-21. Words chosen to describe tempera-tures vary from person to person. We soonknow that we cannot adequately describetemperatures without using numericalvalues to describe the measure of "hot,""cold," "warm," etc.

Describing temperature with numericalvalues rather than words has interestingpossibilities. It is possible to express a_greater sange and variety of temperatures.

Each numeral has a fixed value while the the fo_value of a wolci depends upcm judgment ture isof the user. If temperatures can be ex- somettpressed. as numerals, then instead of esti- eter rr:mates, temperatures can be measured. mornelTemperatures are measured with tiler- meralsmometers. It may seem that to measure therrncthe temperature of the upper atmosphere, expresit is only necessary to send up a ther- mean?mometer, and the temperature would be used tiexpressed as a numerical value, Figure IV- atmosl22_ Unfortunately, all is not that simple. To Tounderstand why, we must find answers to value c

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balloon will become partially inflated asshown in Figure IV-24a. The circumferenceof the balloon can be measured with a pieceof string as shown in Figure IV-24b. Finally,if the bottle-balloon system is removedfrom the pan of warm water and allowedto cool, the balloon will slowly collapse toa position similar to its original position asin Figure IV-7.3. Could the air in thebottle change --olume during this activity?What evidence :supports your answer? Sup-pose the bottle-balloon system were placed

Figure IV-23

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in the refrigerator c you wedict whatmight happen?

Consider these queons: How can youcheck the accuracy ,;!. your Trediction?How %Pas a temperatame change convertedinto al number?

Pill a bottle Vo the tri3 with water. Adda ft w drops of food cc.ioring to make thewatex easier to observt,. Sellect a one-holestopper of the ritht sice to fit tightly intothe bottle. A piece ot f glass tubing about12-15 cm long is pushatit throzgh the holein the stopper so that itiprojects out of thebottom of the stopper ilbout 2 cm (FigureIV-25). Use exttremn care in pushing theglass tubing through law, stopper. To avoidinjury or breakage, do mot force the tubingthrough the stopper. (A small amount ofsoapy water, or glycerine may be used tolubricate the stopper ansd tubing so that thetubing will slide more ea;sil3r.)

The stopper is fitted tightly into themouth of the bottle .luld forced downslightly so that some wr,ter isJ, displaced upinto the glass tubing (Figure IV-26). ThepoSition of the water in the tubing can bemarked With a grease pencil- or a smallpiece of masking tape.

After the bottle has been transferred toa pan of water quite warm to the touch,the system is observed For. changes. 3 to 5

Figura:IV-26

'10

iliinutes later, the position of the liquid inthe tube will be higher than the originalkLosition as illustrated by Figure IV-27.This change in position may be measuredMth a ruler.

14eXt, the bottle is removed from the panof warm water and allowed to cool. TheWater in the tubing may not return to itsQriginal position.

jf it should not, could you offer a pos-sible explanation? Did the water change

iItolume n this activity? How was theteoperature change converted into a num-ber? Remember what we have discussed sofar about density.

We can also use a measure of the physicalDroperties of wire to measure temperature.Take a piece of fine wire (about B & S gauge*24 or #26). About 50 cm of the wire iskisPended horizontally between two firmlyfixed supports, but not tightly stretched,

i$11re IV-28. A weight, such as a smallJlaice can filled with water or sand is sus-Dended from the wire so -that the weightSwings freely. The vertical distance fromthe table surface to the bottom of theWeight is measured with a ruler (Figure

A portion of the wire is then heatedtising a small flame from a candle, alcohollainp or small burner. (Caution: If you

r

carry out this activity, use extreme carewith open flames. Never allow any partof your body or portion of your clothingto come close to a flame. Girls must beespecially careful with their hair.)

If the vertical height of the weight is nowmeasured it shows the weight is lower thanits original position. Next heat a largerportion of the wire by moving the flameback and forth along it slowly. Again, theheight of the weight above the table top ismeasured. What do you predict about thismeasurement?

If the wire is allowed to cool, and theheight of the weight is measured, how doyou predict this measurement will comparewith the original measurement? Be very

Figure IV-28

Figure IV-27 Rgure IV-29

Figure IV-30

careful when you answer the next question.Consider the evidence you have available.Did the wire change volume during thisactivity?

Although generalizing from a small num-ber of observations can be dangerous, itappears that a relationship has been dis-covered. It appears that matter expandswhen warmed and contracts when cooled.The danger of generalizing from so fewobservations will become very apparent ifyou substitute a long rubber band for thewire, or cool the water down to freezing.It also appears that the amount of expan-

96

sion or contraction is related to the amountof temperature change, so not only cantemperature changes be detected, but theamount of change can be measured. Per-haps you can think of some ways to useeach piece of equipment just described asa thermometer to measure temperature?What advantages or disadvantages will eachhave? How might these thermometers beimproved?

Perhaps *the most common therms:it-fie-ters are those constructed of a glass tubefilled with a liquid, usually alcohol or mercu-ry, Figure IV-30. Most of the liquid is con-tained in a bulb attached to one end of a longstem. A very fine opening, called a ca-Pillarytube extends down the center of the longstem. When the liquid expands, it is"pushed down" the capillary, and_ whencooled it contracts and is "pulled" backinto the bulb. The total volume of thecapillary is so small, that a very smallchange in the volume of the liquid pro-duces a large displacement in the positionof the liquid in the capillary. In this waysmall changes of temperature can be de-tected, but since the stem is usually long,these changes can be detected over a largerange of temperatures.

Refinement and miniaturization of theinstruments you have just investigated en-able scientists of our space age to find outa great deal about the upper atmospherewithout actually going there.

Chapter V

WHAT LIGHT CAN TELL US

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the height of something as tall as Saturn V,Figure V-3. You could climb to the top ofthe gantry and measure one tape length at atime until you got down, but this would bedifficult. It would probably be better andeasier to measure this larger distance in-directly.

Space science had its start far back inthe misty beginnings of human history.Ancient man stood alone under the splen-did twinkling of the night sky and he won-dered. The questions that came to his mind,stirring his curiousity, are similar to thethoughts you would have today. Questionsabout stars come to mind easily. How faraway are they? What are they? These andall the other questions can be answered onlyif we measure. But what is there about astar that you can possibly measure?

The invention and development of thetelescope has not changed what we canmeasure. Even with the 200 inch Mt.Palomar light-collector, we still measure thebrightness and position of stars to obtainthe fundamental measurements necessaryto describe space and its content& In addi-tion to these two measurements, by 1800,space scientists learned how to make thelight from a star give off a rainbow its

-741171

Fox Asa._

Figure V-5

spectrum. We get nothing else just bright-ness, position, and spectrum, Figure V-5.

The unequal brightness of the stars iseasily seen by anyone who looks at thenight sky. The luminosities have greatrange. Some stars are so brilliant that theycatch our eye immediately. Others are sodim that they are barely spots in the dark-ness, Figure V-6. Between these extremeswe find all the other possible degrees ofbrightness.

About 1800 years ago Claudius Ptolemyorganized a book that listed the brightnessof every star visible to the ancient astrono-mers. The brightness of a star as seen bythe unaided eye was called the magnitudeof the star. Long before Ptolemy, it hadbeen accepted that the brightness of a starwould be classified as one of 6 differentmagnitudes. A first magnitude star wouldbe extremely bright. About 20 stars werebright enough to be rated 1st magnitude. Astar dimmer than 1st magnitude had ahigher number such as 2nd, 3rd, 41111 or 5thmagnitude. Finally the stars that werebarely visible were called 6th magnitude.When telescopes came into common use,the system of magnitudes had to be ex-tended, for now astronomers were able tosee many stars dimmer than the 6thmagnitude.

Astronomers however were faced with aproblem. They had to figure out jue: what7th magnitude would be. How much dim-mer than 6th magnitude would a 7th mag-nitude star be? In order to do this, thedifference between the brightness of any ofthe other magnitudes had to be measured.

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240

220

200

180

160

140

120

100

80

Figure V-6

60

40

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3 4

MA GN IT UDEFigure V-7

In 1856 Pogson determined that this differ-ence Was 2.5. So a first magnitude star wasabout 2.5 times brighter than a secondmagnitude star. A 1st magnitude star wouldbe 2.5 X 2.5 or 6.3 times brighter than a3rd magnitude star. Use Figure V-7 to de-termine how much brighter than a 7thmagnitude star a 3rd magnitude star is.

Are all stars of the same brightness?If they are then the apparent differences inbrightness are caused by differences in thedistance between the stars and Earth. Closestars would be bright and far away starswould be dim.

It could also be that all stars are thesame distance from Earth, and their dif-ference in brightness is caused by theirchemical make-up.

For a long time man did not know whysome stars appear brighter than others. Theanswer came by studying the position ofthe stars, and their spectra.

Stars are moving all the time. If you goout and look at the night sky and thenlook again an hour later, you will see thatthe stars have moved. We know that thisapparent movement is caused by the rota-tion of Earth.

The patterns of the stars, the constella-tions, appear to stay the same. For thisreason the stars are sometimes called"fixed." In Ptolemy's book "The Alma-gest," he had recorded the position of thefixed stars. This was done by measuringangles.

When we look at the night sky it ap-pears that we are standing at the center ofa black dome which we call the celestialsphere. Since it does appear to be a spherewe can measure position using angles.

In order to use angular measurementyou must choose a starting point. In estab-lishing latitudes and longitudes to measureposition on Earth, the Equator and thePrime Meridian have been chosen as start-ing points. Similarly, the extension ofEarth's equator on to the sky was chosenas one starting point. Any star on this linewould be on the celestial equator (FigureV-8).

The position of any star can be partiallydescribed by measuring the angle from thecelestial equator to the star, as seen fromEarth. The name given to this measure-ment is declination. Since declination canbe above or below the celestial equator, itis called North (÷) declination or South ()declination (Figure V-9). But declinationdoes not do the whole job. If a star isfound at 25° South () declination, itcould be anywhere on the dashed circleshown in Figure V-9.

SPHERE

CELESTIALNORTH POLE

Figure V-8

450 NORTHDECLINATION

CELESTIALNORTH POLE

NORTH CELESHALPOLE

HOURCIRCLE

Figure V-10

NORTHCELESTIALPOLE TERRESTR I AL

NORTH POLE CELESTIALDECLINATIONCIRCLES (NORTH)

TERRESTR I ALEQUATOR

CELESTIALEQUATOR

CELESTIALOUR

CIRCLE

TERRESTR I ALMERIDIANS

25° SOUTHDECLINATION

Figure V-9

A second reference line is employed tolocate star position. This is done by divid-ing the celestial sphere into hour circles asshown hi Figure V-10.

Combining these two systems of imagi-nary lines on thk., celestial sphere (FigureV711), the hour circles correspond to earth

Figure V-11

TERRESTR I ALLATITUDE(SOUTH)

meridians or lines of longitude. Celestialparallels of declination correspond to ter-restrial (earth) latitude.

If you imagine Figure V-10 sliced inhalf at the celestial equator, you have spacecut up like an orange (Figure V-12). Whenthis is done, we are able to measure anglesaround the celestial equator. But we needa starting pomt for space measurements justas we need the Prime Meridian for terres-trial measurement. Astronomers selected

CELESTIAL EQUATOR

Figure V-12

ELESTIAO

the place where the sun appears to crossthe celestial equator OA its trip North.

There are two days each year when thesun is directly over the equator. Thesedays are called equinoxes because the hoursof daylight (12) and the hours of darkness(12) are equal. The equinox that marks thebeginniag of Northern hemisphere Springoccurs when the sun crosses the celestialequator on its way North (Figure V-13).This point is called the vernal equinox andis used as a beginning place in measuringangles eastward along the celestial equator(Figure V-14). These angles are called rightascension and are measured from the vernalequinox to the point where the hem- circleof a star intersects the celestial equator.

Right ascension angles, for conveniencein astronomical measurement by clocks, arealso expressed by hours, minutes and sec-onds. Thus, a right ascension coordinate of-15° would be one hour )f time.

ALDEBARANRIGELBETELGEUSECASTORMERAK

RIGHTASCENSION DECLINATION

60.5° (4h 34') 16° 26' NORTH75.2° (5h 13') 8° 14' SOUTH75.9° (5h 53') 7° 24' NORTH

105.5° (7h 32') 31° 58' NORTH165° (11 h 00') 56° 34' NORTH

Figure V-.1.5

We find, then, that the position of a starcan be described by giving two angles.These angles are called right' ascension anddeclination. The position of some wellknown stars is given in Figure V-15. In1718 Halley discovered that the positions ofthe "fixed' stars were not fixed. He foundthat positions of stars had changed. They

oh were not in the places given in Ptolemy'sAlmagest. This opened a new age in astron-omy. Within 20 years, the distance to astar was measured.

The light from stars can also tell usmuch. If we analyze it we have some ideaof the composition of a star, what it ismade of. When we notice the beauty of arainbow, sunlight falling on raindrops, weare really seeing light broken into a spec-trum. When light passes through triangularshaped glass, the light is broken up into aspectrum. Isaac Newton was the first toFigure V-14

Figure V-16

investigate this. No matter how this is done,the spectra are always in the same order:red, orange, yellow, green, blue, and violet.

You can investigate this "rainbow" ifyon have a glass prism (Figure V-16). Bet-ter still, you can make a simple spectroscopein just a few minutes if you follow the di-rections below. With a spectroscope youcan examine spectra of incandescent lights,,fluorescent lights, sunlight, or other lightsources.

The principle .behind the formation o6spectra is best explained by imagining thatlight has properties similar to waves onwater. When waves come from differentsources, they interfere with each other.Sometimes the light waves add together andmake, bright bands. At other locations theysubtract from each other, producing bandsof darkness. This is what happens whenlight goes through a replica diffractiongrating.

It is one thing to read about spectra. Itis far better to see one for yourself. Aspectrometer can be made easily. Here iswhat you need:

1. Replica diffraction grating This iswhat makes the spectrometer work.If you cannot get one in school, theycan be purchased from scientificsupply houses for about 250, orborrow one from a physics teacher.

2. Razor blades. A double-edge bladecan be broken in half so that thetwo edges can be used. For safetyreasons you may prefer to use twosingle-edge blades.

3. Cardboard box. It must come with.a removable top. The box has to be

. .deep enough to hold your diffractiongrating. This is probably a little

REPLICAGRATING(INSIDE)

over two inches. The box can beany depth more than this. The boxshould also be about twice as long asit is wide. A shoe-box usually doesa fine job.

RAZORBLADES

SLIT SCALE

VIEWINGHOLE

Figure V-17

Cut a slit in the far left side of the nar-row end of the box. The position of theslit is shown in Figure V-17. The slit shouldbe about 1/8 inch wide and 1 inch high.Fasten the razor blades so the slit is verynarrow, less than 1/32 inch if possible.The two edges must be parallel.

Cut a circular hole about % inch indiameter in the near left corner. Makesure that the center of the hole is on astraight line with the slit at the other end.Now cover the eye hole with the replicadiffraction gratMg. Before you tape thegrating in place be sure you have it posi-tioned properly. The rulings should bevr,tical. Make sure you can see a spectrum.Put the top on the box.

At this point you have a spectroscope.If you look in the eyehole, and point theslit at a light source, you will see a spec-trum off to the right. But all you can 6)at this point is look. If you want to be ableto measure, you need a scale. You canmake a scale on any piece of white paper.Mark the paper at the distances shown inFigure V-18. If your spectrometer is

SLITt o'T blend into each other. By definition,the colors are divided at the followingplaces on your scale:Violet less than 4,500Blue 4,500 to 5,000Green 5,000 to 5,700Yellow 5,700 to 5,900Orange 5,900 to 6,100 ARed more than 6,100 A

Place a piece of red cellophane in frontof the slit. Notice if any of the colors areabsorbed. Try other colors of cellophane,or colored glass. In each case, compare thecolor of the absorber and the colors trans-mitted.

2. Look at a flourescent light. Noticethe bright lines on the spectrum.Notice the scale positiom. LoRk forbright green at about 5,000 A., andyellow about 5,800 A.

3. Burn some salt in a gas flame in adark room. Look at the spectrum.This time you get no rainbow, in-stead 3r,pu see a bright yellow line at5,900 A.

In Igil4 Joseph Fraunhoffer was usingan improved version of the spectrometer.When he looked at sunlight, he discoveredthat the entire spectrum was marked byhundreds of black lines. Some were darkerthan others. He made a map of these linesas shown in Figure V-19. If you are inter-ested in spectra and the abbreviationsshown below get yourself a good physicsbook and a chemistry book and read aboutthem

Did you see these lines when you lookedat sunlight through your spectroscope?No. Try, this technique.

Take your spectrometer and fasten apiece of wax paper over the slit lhe pre-cautions given here are necessary. Underno condition should you point the slit ofyour spectrometer directly at the sun.Instead, place a piece of plate glass on topof a sheet of black paper. Line up theglass so that the image of the sun reflectsfrom the surface. Now look at the imageof the sun on the glass. You will probablysee two kinds of black lines. Some runhorizontally through the entire spectrum.These are to be ignored. They are causedby the uneveness of the razor blades in theslit. The vertical black lines are the onesthat made Fraunhofer famous. The darkest

larger, copy Figure V-18. Cut this outand extend the lines until they "reach yourscale. Then mark off ygur scale 4000,5000, 6000, and 7000 A. Rememberthat we measure light spectra in ang-stromsthe different wavelengths of lightgive us different colors. One angstrom is0.00000001 centimeters (Chapter II). Itmay be too dark inside the box to see thescale. If this is true, cut a small rectangularopening, in the top of the box. Thisopening is cut above the scale. Now youare ready to use your spectrometer.

1. Allow light to enter the slit. BECAREFUL. DO NOT LOOK ATTHE SUN. DO NOT ALLOW THEIMAGE OF T.HE SUN TO BE INTHE SLIT. Look at the spectrum onyour scale. Examine it. Notice theorder of the colors. Notice if they

VONIZED Co Hy Fe Hy(4C H) HYDROGEN MAG.+IRON

HYDROGENSODIUM IRONI OXYGEN OXYGEN

V OLE.7 BLUE GREEN

Figure V-19

Ftgure V-20

and clearest should be found in the yellowand in the area where green becomes blue.It took 50 years for human minds to figureout what caused These black lines.

The sun is a sphcrc of hot gases sur-rounded by a layer of cookr gases. Thesurface of the sun, the part we can see,gives off the entire spectrum of light. Weknow that if we blotout the disc of the sun,we can see a layer that glows. This happensnaturally during a solar eclipse, Figure V-20. This outer layer of gases is part of thesun's atmosphere. It is cooler than thesurface. If it was hotter than the sun'ssurface, we would always see the atmos-phere, not just during an eclipse. The dif-ferent elements found in the cooler atmos-phere of the sun cause ate black lines in thesolar spectrum by absorbing some of thecolors radiated from the sun's surface.

YELLOWORANIGE

RED

Figure V-21

For example, when sunlight falls on apicket fence, the fence slats absorb lightfrom the sun. We say "the slats cast ashadow" (Figure V-21). In a way, theelements in the atmosphere of the sun actlike the slats in the fence. They absorblight and make "shadows." But there issomething ver- special about the shadows.When light strikes a wood slat, none of thevisible light goes through the wood. Butwhen the light of the sun passes throughthe solar atmosphere, the gases only stopcertain regions of the spectrum, causingthe black lines as in Figure V-19.

Why are only certain colored linesstopped by the atmosphere of the sun?The answer has to do with the nature ofatoms and the arrangement of their protons,neutrons, and esnecially the electrons. Werepresent atoms with drawings like Figure

ELECTRONIN

ORBIT

NUCLEUS0

Figure V-22

V-22. This is a model of the hydrogen at-om. The electron is in orbit around theproton in the nucleus. The electron remainsthe same distance from the nucleus, just asEarth stays about the same distance fromthe sun. But what would happen to thesize of Earth's orbit if Earth received moreenergy? It would be larger. If an electronreceived energy, it moves away from th-e-nucleus. If an electron loses energy, itmoves toward the nucleus. Electrons cangain or lose energy by absorbing or givingoff light.

In the experiments with the spectrom-eter, you observed the spectrum given offby heated salt. A bright yellow line waspresent. This line, which is really twolines close together, is caused by the elec-trons of the sodium atom losing energyand falling closer to the nucleus. The rea-son that sodium when heated has a differentspectrum than any other substance is thatno other atom has the same number ofelectrons in the same orbits as the sodiumatom. So only the electrons of sodium canmake the moves that give off this array ofbright lines shown in Figure V-23.

Use the same set-up that produced thebright yellow sodium line. Burn salt andobsern the bright yellow line at about5900 A on your scale. Now place a 200watt light one or two feet behind yourburning salt. This time when you look

through your spectromeler you may ob-serve a &it line at 5900 A.

This time the electrons are absorbingenergy- from the light of the bulb,. Sodiumelectrons are gaining energy ..and movingaway from the nucleus. This miorion is theexact opposite of the fall-in 'ictot gave offthe yellowlight. It takes in, cr- absorbs. theyellow 1igh. leaving black limes. The blacklines in surifight that FraurthoYter first no-ticed are cansed the same way.

In 1859 Bunsen (he also iitmented theburner) and Kirchhoff discovered that eachdifferent eement gives off its ovn specialcolors of & spectrum. No two substanceshave the same absorption. Tley all havetheir own set of spectral "shadows." Spec-tra are as good to identify elements asfinger prinEs are to identify peaple. Theyare all diffezent.

By studying the Fraunirnf= lines insunlight, astronomers have fount. 67 of the103 elements we find on Eartii on the sun.But the sun is not the only s5tza. with ab-sorption lines in its spectrum, . We can usethe same methods to obtain the chemicalcoMposition of all stars which yield aspectrum.

We have seen that the only directmeasurements we can make in space arethose that describe the position, the bright-ness, and the spectrum of a star. In Shapesof Tomorrow of this series, you can seehow we use these direct measurements tomake indirect meaairements describing thedistance to stars and their temperatures.

Yellow Orange Red

Figure V-23, A continuous spe4.trum at the top.A bright line spectrum of sodium below. Thedouble line of the sodium atom falls in the yellowregion at about 5,800 A wavelength.

TO THE FUTURE

A Special Word for the Student

Wait! 15k...fore we close, let's pick up anddust ei-lf the heart clock we so quickly andcatektsdy discardeta. And once more set itupon the table next to the InternationalStandards, which are so unbelieveably.pre-cise they can calibrate our new measuringinstruments. Look at it pulsating next tothe gleaming platinum meter so accuratethat fit can measuze the wavelength of theorzin-red line of Krypton 86, and next tothe mysterious atomic clock whose vibra-ting =ystals can measure time to the nanosecorad. (1 CO ) seconds. Take another lookat OUT meart clock that speeds up at timesof stress and slows down during periods ofrest. Perhaps, in a way, it represents theenergy, the work, and the minds of the menand women who created these very accurateinstruments for measuring distances andtimes th,..t we cannot ever hope to experi-ence or "feel."

Next time you sit in front of the tele-vision set and watch the launching of aSpace vehicle, just for a second think ofour heart clock. As the background voicecalls out; 5, 4, 3, 2, 1 Ignition Liftoff, "all systems go," and finally "condi-tions nominal, we have another successfulspace flight." Instead of thinking onlyabout the flash of flame, the billowingclouds of smoke, and the arching beauty ofthe gleaming rocket soaring across the sky,give a thought to the people who haveworked years to make this launch a success.

Think of the project group which hasworked for 2, 3, or more years in order tobring all the experiments and componentstogether for this instant.

We could also think of the experts ofthe world-wide tracking networks readyand waiting for the first "beep" of thesignaling satellite. We may think of thestress engineer, who analyzed, reduceo, andrebuilt each supporting structure to toler-ances only the computer could predict; thedraftsman who designed; the engineer whotested; the mathematician who calculated;the machinist who drilled and ground; theoptician who calibrated the lenses; and thesecretary who filed and typed; these arethe People who made this all possible andwhose hearts speed up a little at the ap-proach of the launch window. Listencarefully to the sounds of outer space,listen to the countdown of Freedom 7, andthe launch of America's first man to orbitEarth. In the midst of whirling corn-pullers,spinning tapes, and crackling intercoms, wehear and "feel" the quickening Pulse of thehuman heart.

Look up and see Echo, Tiros, Apollo,OGO, and many other space explorers asbrilliant points in the starry field, announc-ing the achievements and hopes of thehuman mind.

No, our International Heart Clock is nota worthless standard._ It represents Man inthe Space Agenow ending its first decade.

The material as presented in this publication is representative of the judgments of the authorsand does not express the official policy of the Department of Health, Education and Welfare.

GLOSSARYOF

SPACE RELATED TERMS

A

Absorption The process in which incidentelectromagnetic radiation is retained by asubstance.

Absorption Lines The pattern of darkspectral lines against the background of abright continuous spectrum: produced bya cooler gas absorbing energy ftom ahotter source behind it.

Altitude The height of a position orobject above sea level: (of a star) theangle from the horizon to a star measuredalong a vertical circle.

Anemometer A weather instrument usedto measure wind speed.

Angle The intersection of two lines witha common end point.

Anjstrom (A) .1. unit of length, usedchiefly in expressing short wavelengths,10-8 centimeters.

Aphelion That orbital point farthestfrom the sun when the sun is the centerof attraction. That point nearest the sunis called "perihelion. ' The aphelion ofthe earth is 1.520 x 10" cm from thesun.

Apogee In an orbit about the earth, thepoint at which the satellite is farthestfrom the earth; the highest altitudereached by a sounding rocket.

Astronomical Unit (abbr AU) In theastronomical system of measures, a unitof length usually defined as the distancefrom the Earth to the Sun, approximately92,900,000 statute miles or 14,960,000kilometers. It is more precisely defmedas the unit of distance in terms of which,in Kepler's Third Law, n2 a3 = k2 (1 + m),the semimajor axis a of an elliptical orbitmust be expressed in, order that the mi-merical value of thc...-Gaussian constant,k, may be exactly 0.01720209895 whenthe unit of time is the ephemeris day.

In astronomical units, the mean dis-tance of the Earth from the Sun, calcu-lated from the observed mean motion nand adopted mass m is 1.00000003.

Atmosphere The envelope of air sur-rounding the earth; also the body of gasessurrounding or comprising any planet orother celestial body.

Atom The smallest particle of an elementthat exhibits the properties of the ele-ment.

Atomic Clock A precision clock that de-pends for its operation on an electricaloscillator (as a quartz crustal) regulatedby the natural vibration frequencies of anatomic system (as a beam of cesium atomsor ammonia molecules).

Axis (pl. axes) 1. A straight line aboutwhich a body rotates, or around which aplane figure may rotate to produce asolid; a line of symmetry. 2. One of aset of reference lines for certain systemsof coordinates.

Babylonia An ancient empire in SWAsia, in the lower Euphrates valley. Theperiod of greatness, 2800 BC to 1750BC.

Barometer A common instrument usedto measure the pressure exerted by theearth's atmosphere. Includes the mercuryand aneroid barometers.

Brightness A measure of the luminosityof a body.

Bunsen, Robert Wilhelm 1811 - 99. AGerman chemist.

Camera Angle A major characteristic of acamera that limits the view of a particularcamera by a predetermined setting.

Celestial Equator The great circle on thecelestial sphere midway between thecelestial poles.

Clepsydra A device for measuring timeby the regulated flow of water or mercurythrough a small.opening.

Compression The half of a sound wave inwhich air or medium is compressed togreater than its normal density.

Declination The angular distance of anobject north or south of the celestialequator and measured in degrees alongthe object's hour circle.

Degree A unit on a suggested scale ofmeasurement. Used to describe themeasurement of temperature, time, dis-tance, and angles.

Density The mass of a substance perunit volume.

Diffraction Grating A metal or plasticplate containing ruled parallel lines usedto bend or spread light waves after thelight has passed through a narrow slit inan opaque body.

Eccentricity The amount by which afigure deviates from a circular form, as anorbit.

Echo-I A large plastic balloon with adiameter of 100 feet launched on August12, 1960 by the United States and in-flated in orbit. It was launched as a pas-sive communications satellite, to reflectmicrowaves from a transmitter to a re-ceiver beyond the horizon.

Ecliptic The apparent annual path of thesun among the stars; the intersection ofthe plane of the earth's orbit with thecelestial sphere.

This is a great circle of the celestialsphere inclined at an angle of about23°27' to the celestial equator.

Electromagnetic Radiation Energy prop-agated through space or through materialmedia in the form of an advancing dis-turbance in electrical and magnetic fieldsexisting in space or in the media. Alsocalled simply "radiation."

Electron The subatomic particle thatpossesses the smallest possible electriccharge.

The term "electron" is usually reversedfor the orbital particle whereas the term"beta particle" refers to -a particle of thesame electric charge inside the nucleus ofthe atom.

Ellipse A plane curve constituting, thelocus of all points the sum of whose dis-tances from two fixed point called "foci"is constant; an elongated circle.

The orbits of planets, satellites, plane-toids, and comets are ellipses; center ofattraction is at one focus.

Equinoxes The two points orA the celestialsphere where the celestial equator inter-sects with the ecliptic.

Explorer A series -of scientific satellitesdesigned to explore outer space.

Foucault, Jean Bernard Leon 1819 - 68,French Physicist.

Fraunhofer, Joseph von 1787 - 1826,German optician and physicist.

Fraunhofer Lines Dark lines crossing thecontinuous spectrum of the sun or simila:source. The lines result from the absorp-tion of some wavelengths by layers ofcooler gases.

Freedom 7 The first American mannedspace flight. Piloted by Alan B. Shepardon May 5, 1961. This suborbital missionlasted 19 minutes and reached an altitudeof 116 miles.

Frequency The number of waves leavingor arriving at a position per unit of time.

Friction The force that resists the slidingor motion of one object in contact withanother.

Galileo 1564 - 1642, Italian physicist anda stronomer.

Geiger Counter An instrument for de-tecting and counfing ionizing particles,used to determine the degree of radio-activity.

Gnomon A vertical shaft or stick usedfor determining the altitude of the sun orthe position of a place by noting thelength of a shadow. Used as part of asundial.

-

Gravity The force imparted by the earthto a mass on, or close to the earth.Since the earth is rotating, the force ob-served as gravity is the resultant of theforce of gravitation and the centrifugalforce arising from this rotation.

Grid System A system of lines used todetermine dimension or direction bymeans of a scale.

Halley, Edmund 1656 - 1742, BritishAstronomer.

Hour Angle The angle between thecelestial meridian and the hour circleof a celestial object.

Huygens, Christian 1629 95, Dutchmathematician, physicist, and astronomer.

Hypothesis An idea or guess proposed asan explanation for the occurrence ofphenomena.

Inertia The tendency of an object, as aresult of its mass, to continue in motionat a constant speed or to remain at rest.

Kilo A prefix meaning "thousand" usedin the metric or other scientific systemsof measurement.

Kirchoff, Gustav Robert 1824 - 87,German physicist.

Latitude The angle from earth's equatorto a point on Earth as measured along aterrestial meridian.

Light Year The distance light travels inone year at rate of 186,000 miles persecond (300,000 kilometers per second).Equal to 5.9 x 10" miles.

Longitude The angle between the Primemeridian and the terrestial meridianthrough a point on earth.

Luminosity The brightness of a star orobject as compared to a standard such asthe sun.

Lunar Eclipse The partial or total obseura-tion of the sun's light on the moon,caused by the passage of the earth be-tween the sun and moon.

Mariner The initial unmanned explorationof the planets, is being conducted in theUnited States Under the Mariner program.Mariner 2, launched August 26, 1962,passed within 21,000 miles of Venus onDeeember 14, 1962, and radioed to earthinformation concerning the infrared andmicrowave emission of the planet, and thestrength of the planet's magnetic field.

On July 34, 1965, Mariner IV snappedthe first close-up pictures ever taken ofanother planet as it sped by Mars at dis-tances ranging from 10,500 miles to7,400 miles. Beside providing close-up

photographs of Mars and scientific datapertaining to the physical characteristics,Mariner IV confirmed the original findingof Mariner II relative to interplanetaryspace. Future flyby missions to bothVenus and Mars are planned.

Mass The measure of the amount ofmatter in a body, thus its inertia. Theweight of a body is the force with whichit is attracted by the earth.

Mega A prefix meaning multiplied byone million as in "megacycles."

Meridian A great circle which passesthrough the zenith directly north andsouth.

Micro 1. A prefix meaning divided byone million. 2. A prefix meaning verysmall as in "micrometeorite."

Micrometeorite A very small meteoriteor meteoritic particle with a diameter ingeneral less than a millimeter.

Nanosecond (Abbr nsec) 10 second.Also called `millimicrosecond."'

NASA (Abbr) National Aeronautics andSpace Administration.

Neutron A subatomic particle with noelectric charge, and with a mass slightlymore than the mass of the proton.

Protons and neutrons comprise atomicnuclei; and they are both classed asnucleons.

Newton, Sir Isaac 1642 1727, Britishscientist, mathematician, and philosopher.

North Pole The point at which northernend of earth's axis intersects the surfaceof earth.

Nucleus The positively charged core of anatom with which is associated practicallythe whole mass of the atom but only aminute part of its volume.

A nucleus is composed of one or moreprotons and an approximately ecwal num-ber of neutrons.

0OGO The Orbiting Geophysical Observa-

tories are designed to broaden our knowl-edge of Earth and space and how the suninfluences and affects both. OGO is de-signed to carry about 20 different experi-

ments. The advantage of OGO is that itmakes possible the observation of nu-merous phenomena simultaneously forprolonged periods of time. OGO I waslaunched September 4, 1964 and OGO IIOctober 14, 1965.

Orbit 1. The path of a body or particleunder the influence of a gravitationalor other force. For instance, the orbitof a celestial body is its path relative toanother body around which it revolves.2. To go around the earth or other bodyin an orbit.

Orbital Elements A set of 7 parametersdefining the orbit of a satellite.

Pendulum An object suspended from afixed point able to move back and forthby the action of gravity and momentum.

Perigee That orbital point nearest theearth when the earth is the center ofattraction.

That orbital point farthest from theearth is called 'apogee." Perigee andapogee are used by many writers in re-ferring to orbits of satellites, especiallyartificial satellites, around any planets orsatellite, thus avoiding coinage of newterms for each planet and moon.

Perihelion That orbital point nearest thesun when the sun is the center of attrac-tion.

That orbital point farthest from the sunis called "aphelion." The term "peri-helion" should not be confused with"parhelion," a form of halo.

Period The interval needed to .corripletea cycle. Often used . in reference to timeof complete orbit.

Pico A prefix meaning divided by onemillion million.

Precession Change in the direction of theaxis of rotation of a spinning body, as agyroscope, when acted upon by a torque.

The direction of motion of the axis issuch that it causes the direction of spin ofthe gyroscope to tend to coincide withthat of the impressed torque. The hc.ri-zontal component of precession is called"drift," and the vertical component iscalled "topple."

Pressure (Abbr p) As measured in avacuum system, the quantity measuredat a specified time by a so-called vacuumgage, whose sensing element is located ina cavity (gage tube) with an openingoriented in a specified direction at aspecified point within the system assum-ing a specified calibration factor.

Primary Body The spatial body aboutwhich a satellite or other body orbits,or from which it is escaping, or towardswhich it is falling.

The primary body of the moon is theearth; the primary body of the earth isthe sun.

Proton A positively-charged subatomicparticle having a mass slightly less thanthat of a neutron but about 1847 timesgreater than that of an electron. Es-sentially, the proton is the nucleus of thehydrogen isotope 1H1 (ordinary hydro-gen stripped of its orbital electron). Itselectric charge (+4.8025 x 10 ° esu) isnumerically equal, but opposite in sign,to that of the electron.

Protons and neutrons comprise atomicnuclei; they are both classed as"nucleons."

Protractor An instrument, graduated indegrees of arc, for plotting or measuringangles.

Proxima Centauri A star in the constella-tion Centaur at a distance of about 4.3light years.

Ptolemy, Claudius 127 - 151 AD, Greekmathematician, astronomer, and geogra-pher.

Radiometer A device used to measuresome property of electromagnetic radia-tion. In the visible and ultraviolet regionsof the spectrum, a photocell or photo-graphic plate may be thought of as aradiometer. In the infrared, .solid statedetectors such as photoconductors, leadsulfide cells and thermocouples are used,while in the radio and microwave regions,vacuum tube receivers, often with para-metric or maser preamplifiers, are themost sensitive detectors of electromag-netic radiation.

Radiosonde A balloon-borne instrumentfor the simultaneous measurement andtransmission of meteorological data.

Ranger A program designed to send backto Earth a number of high-resolutionpictures of the Moon's surface, and toshow features at least one-tenth to one-hundredth the size of features discerniblefrom Earth. Ranger VII was successfulon July 31, 1964. Ranger VIII was suc-cessful in meeting its objectives on Feb-ruary 20, 1965 and Ranger IX on March24, 1965. More than 17,000 high resolu-tion photographs were received from thethree satellites.

Rarefaction The half of a sound wave inwhich the air or medium is expanded toless than its normal density.

Refraction The bending of a beam oflight as it passes from one medium intoanother in which the index of refractionis different.

Relative Humidity (Abbr rh) The (dimen-sionless) ratio of the actual vapor pressure

t' the air to the saturation vapor pressure.Rendezvous The event of two or more

objects meeting at a preconceived timeand place.

A rendezvous would be involved, forexample, in servicing or resupplying aa space station.

Resolving Power The ability of a tele-scope or lens system to separate ob-jects which are very close together.

Resonance 1. The phenomenon of ampli-fication of a free wave or oscillation of asystem by a forced wave or oscillation ofexactly equal period. The forced wavemay arise from an impressed force uponthe system or from a boundary condition.The growth of the resonant amplitude ischaracteristically linear in time. 2. Of asystem in forced oscillation, the conditionwhich exists when any change, howeversmall, in the frequency of excitationcauses a decrease in the response of thesystem.

Reticle The crosses located on the gridsystem of the Ranger cameras. Used todetermine distance and direction by scale.

Revolution Motion of a celestial body inits orbit; circular motion about an axisusually external to the body.

In some contexts the terms "revolu-tion" and "rotation" are used inter-changeable; but with reference to themotions of a celestia. 3ody, "revolution"refers to the motion in an orbit or aboutan axis external to the body, while"rotation" refers to motion about anaxis within the body. Thus, the earthrevolves about the sun annually and ro-tates about its axis daily.

Right Ascension The angle as measuredalong the celestial equator from thevernal equinox eastward to the hourcircle of the celestial object.

Rotation Turning of a body about anaxis within the body, as the daily rota-tion of the earth. See Revolution.

Satellite 1. An attendant body that re-volves about another body, the primary;especially in the solar system, a secondarybody, or moon, that revolves about aplanet. 2. A man-made object thatrevolves about a spatial body, such as anExplorer I or a TIROS satellite orbitingabout the earth.

Saturn A family of launch vehicles de-veloped by the U.S. to ultimately placethree men on the moon.

Scale A reduction or increase in size ordimension of an object in proportionresulting in a model.

Sideral Day The time or interval betweentwo consecutive meridian crossings of astar.

Solar Eclipse The partial, total, or an-nular obscuration of the sun's light onthe earth by the passage of the moonbetween earth and the sun.

Solar Wind A stream of protons con-stantly Moving, outward from the sun.Synonymous with solar plasma.

Solar System The group of planets andtheir satellites, and other celestial objectswhich are under the gravitational in-fluence of the sun.

Sounding Rocket A rocket designed toexplore the atmosphere within 4,000miles of the earth's surface.

Space 1. Specifically, the part of theuniNrerse lying outside the limits of the`iirth's atmosphere. 2. More generally,

the volume in which all spatial bodies,including the earth, move.

Spacecraft Devices, manned or unmanned,which are designed to be place(' into anorbit about the earth or into a t jectoryto another celestial body.

Spectrometer An instrument which meas-ures some characteristics such as intensity,of electromagnetic radiation as a functionof wavelength or frequency.

Spectrum 1. In physics, any series ofenergies arranged according to wavelength(or frequency); specifically, the series ofimages produced when a beam of radiantenergy, such as sunlight, is dispersed by aprism or a refraction grating. 2. Shortfor "electromagnetic spectrum" or forany part of it used for a specific purposeas- the 'radio spectrum' (10 Ithocycles to300,000 megacycles).

Star Transit The passage of a star acrossthe celestial meridian.

Sundial An instrument for indicating thetime of day from the position of a shadowcast by the sun.

Surveyor The United States program forthe scientific exploration of the surfaceand subsurface of the moon. Surveyorwas dc,igni;d ":;) soft land on the moon andexplore the physical, chemical, andmineralogical properties at the landingsite. This information was relayed backto Earth by means of extremely highresolution photographs. These picturesrevealed lunar particles a few centimetersin size.The Surveyor missions:Surveyor I June 1,

1966Surveyor II September Unsuccessful

20, 1966Surveyor III April 19,

1967Surveyor IV July 16, Unsuccessful

1967Surveyor. V September

10, 1967Surveyor VI November

11, 1967Surveyor VII January

10, 1968The successful Surveyor missions have re-turned to Earth thousands of photographsof the lunar surface as well as classicphotographs of Earth.

Telescope An optical or radio instrumentused to observe celestial objects.

Temperature A measure of the averageenergy of motion of the molecules of asubstance.

Thermometer Any instrument used tomeasure the expansion and contractionof a substance due to changes in the mo-tion of molecules.

TIROS (Television Infra Red ObservationSatellite) A series of United Statesmeteorological satellites designed to ob-serve the cloud coverage of the earth andmeasure the heat radiation emitted bythe earth in the infrared.

Troposphere That portion of the atmos-phere from the earth's surface to thetropopause; that is, the lowest 10 to 20km of the atmosphere. The troposphereis characterized by decreasing temperaturewith height, appreciable vertical wind mo-tion, appreciable water vapor content,and weather. Dynamically, the tropo-sphere can be divided into the followinglayers: surface boundary layer, Ekmanlayer, and free atmosphere.

U

V

'Vanguard I Launched in 1958, analysisof the orbit this satellite revealed thatEarth is not symmetrically oblate, butbulges in the southern hemisphere.

Vernier Scale A movable, graduatedscale, used for the measuring of fractionalunits of the primary scale.

Volume The size or measure of space ormatter in three dimensions.

Wavelength The distance from one pointon a wave to the corresponding point onthe next wave.

Weight The force with whioh an earth-bound body is attracted toward the earth.

Weightlessness A condition in which noacceleration, whether of gravity or other,force, can be detected by an observerwithin the system in question.

Any object falling freely in a vacuum isweight1ess, thus an unaccelerated atel-lite orbiting the earth is "weightless" al-though gravity affects its orbit. Weight-lessness can be produced within theatmosphere in aircraft flying a parahoPcflight path.

X

Zenith That point on the celestial spherevertically overhead. The point 180° fromthe zenith is called the "nadir."

119

107-

AN AEROSPACE BIBLIOGRAPHY

Abell, George, Exploration of the Universe.New York: Holt, 1966.

Adler, Irving, Seeing the Earth from Space.New York: Day, 1962.

Asimov, Isaac, The Double Planet. NewYork: Abe lard-Schuman, 1960.

, Satellites in Outer Space. NewYork: Random, 1964.

Astronauts Themselves, The, We Seven.New York: Simon & Schuster, 1962.

, Aviation Weather for Pilots andFlight Operation Personnel. Washington:Superintendent of Documents, 1965.

Bell, Joseph N., Seven Into Space. NewYork: Hawthorn, 1960.

Bergaust, Erik, Reaching for the Stars.New York: Doubleday, 1961.

Blair, Thomas A. and Robert G. Fite,Weather Elements. Englewood Cliffs,N.J.: Prentice Hall, 1965.

Cantylaar, George, Your Guide to theWearher. Cranbury, N.J.: A. S. BarnesCo., 1964.

Chester, Michael, Rockets and Spacecraftof the World. New York: Norton, 1964.

Day, John H., The Science of Weather.Reading, Mass.: Addison-Wesley, 1966.

Egan, Philip, Space for Everyone. Chicago:Rand McNally, 1961.

Frutkin; 'Arnold W., International Coopera-tion in Space. Englewood Cliffs, N.J.:Prentice, 1965.

Gamow, George, Gravit;. New York:Doubleday, 1962.

Gat land, K. W. editor, Spaceflight Today.Fallbrook, Cal.: Aero, 1964.

Glasstone, Samuel, Sourcebook on SpaceScience& Princeton, NJ.: VanNostrand,1965.

Goddard, Robert H., Rocket& New York:American Rocket Society, 1946. (Reprintof 1919 and 1935 Smithsonian Reports)

Hawkins, Gerald S., Splendor in the Sky.New York: Harper & Row, 1961.

Hicks, Clifford B., The World Above. NewYork: Holt, 1965.

Hoyle, Fred, Astronomy: A History ofMan's Investigation of the Universe. NewYork: Doubleday, 1962.

, Of Men and Galaxies. Seattle:University of Wh -hington, 1964.

Huffer, Charles M. and others, An Introduc-tion to Astronomy. New York, 1967.

Ley, Willy, Rockets, Missiles, and SpaceTravel. New York: Viking Press, 1961.

Longstreth, T. Morris, Understanding theWeather. New York: Collier Books, 1962.

Mehrens, H. E., The Dawning of the SpaceAge. Ellington AFB, Texas: Civil AirPatrol, 1963.

Meitner, John G. editor, Astronautics ForScience Teachers. New York: Wiley,1965.

, Meteorology for Army Aviation.Washington: Superintendent of Docu-ments, 1963.

Moore, Patrick, Guide to Mars. New York:Macmillan, 1961.

, A Guide to the Planets, NewYork: Norton, 1960.

, Picture History of Astronomy.New York: Grosset, 1961.

The Solar System. New York:Criterion, 1961.

Newlon, Clarke, Famous Pioneers in Space.New York: Dodd, Mead, 1963

Pickering, James S., Astronomy for Ama-teur Observers. New York: Fawcett,1960.

Pothecary, LJ.W. The Atmosphere in Ac-tion. New York: St. Martin's Press, 1965.

Richardson, Robert S., Astronorn,y in Ac-tion. New York: McGraw-Hill, 1962.

Riehl, Herbert, Introduction to the Atmos-phere. New York: McGraw-Hill, 1965.

, Space Science Series, 14 books,New York: Holt, 1965.Al- endt, Myrl H., The Mathematics of

, pace Exploration.Emme, Eugene M., A History of Space

Flight.Faget, Max, Manned Space Flight.Gardner, Marjorie H., Chemistry in the

Space Age .

Goodwin, Harold Leland, The Images ofSparo

Henry, James P., Biomedical Aspects ofSpace Flight.

Hunter II, Maxwell W., Thrust Into Space.Hymoff, Edward, Guidance and Control

of Spacecraft.Jaffe, Leonard, Communications in Space.Naugle, John E.,. Unmanned Space Flight.Stern, Phillip D., Our Space Environment.Sutton, Richard M., The Physics of Space.Wedger, Jr., William K., Meteorological

Satellites.

Youug, Richard S., Extraterrestrial Bi-ology.

Stine, G. Harry, A Handbook of ModelRocketry. Chicago: Follett, 1965.

Thompson, Phillip and Robert O'Brien,Weather. Morristown, N.J.: Silver Bur-dett, 1965.

Trinklein, F. E. and C. M. Huffer, ModernSpace Science. New York: Holt, 1961.

Vaeth, J. Gordon, Weather Eyes in the Sky.New York: Ronald, 1965.

SELECTED REFERENCES, Aerospace Age Dictionmy, The,

Clarke Newton, complier. New York:Watts, 1965.

, Aerospace Education Bibliogra-phy, 3rd Edition, EP-35. Washington:Superintendent of Documents.

, La Rousse Encylopedia of As-tronomy, Lucien Budaux and G. De-Vaucouleurs, editors, New York: Putnam,1962.

Moser, Beta C., Space-Age Acronyms. NewYork: Plenum, 1964.

122

PERIODICALSAviation Week and Technology. Weekly.

cio Fulfillment Manager. PO Box 430,Highstown, N.J. 08520. $8 per year.

Technology Week. Weekly. AmericanAviation Publications, 1001 VermontAvenue, N.W., Washington, D.C. 20005.$5 per year.

Review of Popular Astronomy. Six times ayear. Sky Map Publications, 214 SouthBemiston, St. Louis, Missouri 63105. $4per year.

Sky and Telescope. Monthly. Sky Publish-ing Corporation, 49-51 Bay State Road,Cambridge, Mass. 02138. $6 per year.

Skylights. 9 times a year. National Aero-space Education Council, 616 ShorehamBuilding, 806 15th Street, N.W., Wash-ington, D.C.

Spaceflight. 6 times a year. Sky Publish-ing Corporation, 49-51 Bay State Road,Cambridge, Mass. 02138. $3.50 per year.

OTHER BOOKS OF THIS SERIES, What's Up There. Washington:

Superintendent of' Documents, 1964.,From Here, Where. Washington:

Superintendent of Documents, 1965.Shapes of Tomorrow, The. Wash-

ington: Superintendent of Documents,1967.

AAerobee, 88Albategnius, 47Almagest, 101, 103Alphonsus, 47, 49anemometer, 85angstrom, 19, 25, 105angular degrees, 8aphelion, 31, 40-42apogee, 42, 43Apollo, 26apparent motion, 8astronomical unit, 40

measurement of, 40, 41Atlas of the Moon, 61atmosphere, 84

clouds, 85Mars, 74samples, 82troposphere, 81upper, 81

atmospheric density, 88-91atom, 107

electron, 107neutron, 107nucleus, 107proton, 107

atomic clock, 109axis, 6

Babylonia, 4barometer, 83, 85binary number, 73, 74brightness, 100Bunsen, 107

calendar, 4lunar, 5

celestial equator, 101-103clepsydra, 10clock,

atomic, 107electrical, 21hour glass, 10mechanical, 10, 12shadow, 8sundial, 8water, 10, 21

clouds, 75-77, 85compression, 71-73crescent moon, 32-37Crookes radiometer, 85

INDEX

declination, 101-103density, 85-96diffraction grating, 104, 105direct measurement, 38, 99drop time, 21

Earth,altitude, 12aphelion, 31, 40-42axis, 6, 12, 13, 32density, 12eccentricity, 40-43Equator, 13, 101latitude, 10, 102longitude, 102North Pole, 13, 27orbit, 7, 32, 40perihelion, 31, 40-42phases, 7Prime Meridian, 101, 102revolution, 7, 31rotation, 4, 7, 10seasons, 7

eccentricity, 40-43Echo I, 3, 42eclipse, 41Egypt, 4electrical clock, 21electron, 107ellipse, 31Equator, 13equatorial ring, 9equinox, 103errors, 19, 38

experimental, 48, 49measurement, 39, 42, 72

Explorers, 43, 81, 86

first quarter, 32-37forces,

friction, 12gravitational, 12

Foucault, 12pendulum, 12

Fraunhofer, 105, 107lines, 105

Freedom, 7, 109frequency, 72friction, 12From Here, Where, 11full-moon, 32-37

123

11 0

Galileo, 11, 21gases, 83-92

density, 83-96pressure, 83-96temperature, 83-96volume, 83-96

Geiger counter, 85gibbous moon, 32-37gnomon, 9Goddard, Robert H., 83, 85gravitational force, 12Greenwich, England, 28, 29

Halley, 103hour angle of the sun, 27hour circle, 102, 103Huygens, 21hypothesis, 7, 70, 89

indirect measurement, 38, 100inertia, 12instruments, 85

anemometer, 85barometer, 83Crookes radiometer, 85Geiger counter, 85metric ruler, 65micrometer, 39precision of, 19protractor, 65radiosonde, 77ruler, 65telescope, 100thermometer, 83tuning fork, 70-72vernier scale, 39, 40

Kirchhoff, 107

L.latitude, 10launch window, 14least count, 39light measurements, 100, 101light year, 13longitude, 102luminosity, 100

magnetic radiation, 99Mariner IV, 20, 22, 74Martian atmosphere, 91Mars, 20mass, 86-91Maya, 5measurement, 19

angstrom, 19, 25degrees, 26, 27direct, 38, 39indirect, 38, 100light, 103, 104light year, 13nanosecond, 19, 25scale, 49standard, 22units, 19

mechanical clock, 10, 12meridians, 8

Prime, 8, 101, 102terrestrial, 8

metric ruler, 65micrometer. 39Moon, 32

Atlas, 61crescent, 32-37first quarter, 32-37full, 32-37gibbous, 32-37longitude, 45new, 32-37third quarter, 32-37waning, 32-37waxing, 32-37

motion of Eart1:,

nanosecond, 19, 25NASA/Goddard Spaze

Flight Center, 4, 7neutron, 107new mOon, 32-31Newton, 12,North Pole, 13, 27North Star, 10, 22NOrthern Hemisphere, 7nucleus, 107

0OGO, 4orbits, 40

Earth, 7, 32, 40satellites, 4143

pendulum, 10-13, 21average period, 12bob, 10Foucault, 12period, 10, 11

perigee, 42, 43perihelion, 31, 40-42period of the pendulum, 12Pogson, 101Polaris, 10, 22precision of instruments, 19pressure, 77, 85-96primary scale, 39, 40Prime Meridian, 8, 101, 102proton, 107protractor, 27, 39, 65Proxima Centauri, 13Ptolemaeus, 44, 47Ptolemy, 100

Alrnagest, 101, 103

Q

radiation,light; 99magnetic, 99

radiosonde, 77Ranger IX, 20, 44-61

altitude, 45camera A, 45camera angle, 45grid north, 45grid system, 45resolution, 45, 46reticle, 45, 46scales, 45

rarefaction, 70-73refraction of light, 38rendezvous, 14

rocket, 14spacecraft:14

resolution, 45resonance, 71, 72revolution, 7, 31right ascension, 103rotation, 10, 31ruler, 38, 47, 65, 95

sand glass, 10

Echo I, 3, 42

124

Explorer, 43, 81, 86Mariner IV, 20, 22, 74OGO, 4Ranger IX, 20, 44-61Surveyor, 50Tiros, 75-79Vanguard, 73

satellite orbit, 42, 43apogee, 42, 43eccentricity, 40-43mean distance, 42, 43perigee, 42, 43

Saturn V, 99, 100scale measurement, 49scientific notation, 13seasons, 7shadows,

lengths, 6, 49Shapes of Tomorrow, 27, 107sideral day, 7, 31solar,

day, 7, 31eclipse, 32, 106noon, 8system, 22time, 10wind, 69, 70, 83

solar spectrum, 106, 107sounding rockets, 81, 82, 89-91sound waves, 70

compressions, 70-73frequency, 70-73rarefactions, 70-73resonance, 70-73wavelength, 70-73

space,mathematical model, 70

spacecmft rendezvous, 14spectrum, 103-107spectroscope, 104-107

diffraction grating, 104, 105model, 104

speed of sound, 72, 73standard heart time, 19, 21standard of measurement, 72star,

absorption lines, 105apparent motion, 101brightness, 101day, 71, 31declination, 101-103luminosity, 101magnitude, 101North Star, 10, 22Polaris, 10, 22

Proxima Centauri, 13spectrum, 103-107

sun,apparent position, 8, 27hour angle, 27

sundial, 8-10equatorial ring, 9gnomon., 9model, 9

Surveyor, 50system,

earth-atmovhere, 81operating, 81, 82

telescopes, 101temperature, 83-96thermometer, 83, 85-96third quarter moon, 32-37time,

drop, 21hour circles, 26, 27hours, 27kilo, 19-22local, 28mean, 32mega, 19-22midnight, 26-29minutes, 27nanoseconds, 19, 25shadows, 8, 91solar, 10standard heart, 19, 20

TIROS (Television InfraRed Observation Satellite)75-79

troposphere, 81tuning fork, 70-72

Units of measurement, 19upper atmosphere, 81

VVanguard I, 73vernier, 49, 40

least count. 39, 40primary scale, 39, 40scale, 39, 40

volume, 86-96

waning moon, 32-37water clock, 10, 21

clepsydra, 10wavelength, 104-107waxing moon, 32-37weight, 86-91What's Up There?, 13

XYZ

125

112