Apollo-Soyuz Pamphlet No. 5 the Earth From Orbit

8/8/2019 Apollo-Soyuz Pamphlet No. 5 the Earth From Orbit

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Apollo-Soyuz ^sflwtiPamphlet No.5: *****TheEarth fromOrbit(NASA-EP-137) APOLLO-SOYDZ PAMPHLET NO. 5:

THE EAETH F R O M OBBIT (National Aeronauticsand Space Administration) 67 p MF A01; SODHC set of 9 volumes CSCL 22A Dnclas

G3/12 24993

N78-27151


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Apollo-SoyuzExperimentsInSpace

This is one of a series of ninecurriculum-related pamphletsfor Teachers and Studentsof Space ScienceTitles in this series ofpamphlets include:EP-133 Apollo-Soyuz Pamphlet No. 1: The FlightEP-134 Apollo-Soyuz Pamphlet No. 2: X-Rays, Gamma-RaysEP-135 Apollo-Soyuz Pamphlet No. 3: Sun,Stars, In BetweenEP-136 Apollo-Soyuz Pamphlet No. 4: Gravitational FieldEP-137 Apollo-Soyuz Pamphlet No. 5: The Earth from OrbitEP-138 Apollo-Soyuz Pamphlet No. 6: Cosmic Ray DosageEP-139 Apollo-Soyuz Pamphlet No 7: Biology inZero-GEP-140 Apollo-Soyuz Pamphlet No. 8: Zero-G TechnologyEP-141 Apollo-Soyuz Pamphlet No. 9: General Science

OnThe Cover The Arabian Peninsula and the Red Seaas V i e w e d from Apollo-Soyuz


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Apoilo-SoyuzPamphlet No. 5:The Earth fromOrbit

Prepared by Lou Wil l iam s Page and Thornton Page FromInves t igato rs ' Repor ts o f Exp er im en ta l R es u l t s and Withthe Help of Adv is ing Teachers

NASANational Aeronautics andSpace Admin is t ra t ionWash ing ton , D.C. 20546October 1977


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Fo r sale by the Super intendent of Documents,U.S. Government Printing Off ice, Washington, D.C. 20402(9-Part Set; Sold in Sets Only)Stock Number 033-800-00688-8


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Preface

The Apo llo-Soyuz Test Project (A STP), w hic h flew in Ju ly 1975, arousedconsiderable pub lic interest ; first, because th e space rivals of the late 1950'san d 1960's were working together in a jo int endeavor , and second, becausetheir mutual efforts included developing a space rescue system. The ASTPalso included signif icant scientif ic experiments, the results of which can beused in teaching biology, physics, and mathematics in schools an d colleges.

This series of pamphlets discussing th e Apollo-Soyuz mission and experi-men t s is a set of curriculum supplements designed fo r teachers, supervisors,curr i cu lum specialists, and textbook writers as w ell as for the general pu bli c.Nei ther textbooks nor courses of study, these pamphlets are intended toprovide a rich source of ideas, examples of the scientif ic method, pert inentreferences to standard textbooks, an d clear descriptions of space experiments.In a sense, they may be regarded as a pioneering form of teaching aid. Seldomhas there been such a forthright effort to provide, direct ly to teachers,cu r r i cu l u m- re l ev an t reports of current scientif ic research. Hig h schoolteachers who reviewed the texts suggested that advanced students who areinterested mig ht be assigned to study one pam phlet and report on it to the restof the class. After c lass discussion, studen ts mig ht be assigned (w itho utaccess to the pamphle t ) one or more of the "Questions fo r Discussion" fo rformal or informal answers, thus stressing the applicat ion of what waspreviously covered in the pa mphl e t s .

The authors of these pamphlets are Dr. Lou W i l l i a ms Page , a geologist, andDr. Thornton Page, an astronomer. Both have taught science at severaluniversi t ies an d have publ i shed 14 books on science fo r schools, colleges, an dth e general reader, inclu din g a recent one on space science.

Technical assistance to the Pages was provided by the Apollo-SoyuzProgram Sc ient i s t , Dr . R . Thomas G iul i , and by Richard R. Ba ldw in,W. Wilson Lauderdale, and Susan N. Montgomery, members of the group atth e N A S A L y n d on B . Johnson Space Center in Houston wh ich organized th escientists ' part ic ipat ion in the ASTP and publish ed their reports of e xperim en-ta l results .

Selected teachers from high schools and univers i t ies through out th e Uni t e dStates reviewed th e pa mphl e t s in draft form. They suggested changes inwording, the addit ion of a glossary of terms u n f am i l i a r to students, andi mp ro v emen t s in diagrams. A list of the teachers and of the scientif ic inves-t igators who reviewed th e tex ts fo r accuracy fol lows this Preface.This set of Apollo-So yuz pam phle ts was ini t ia ted and coordinated by Dr.Frederick B. Tu tt le , Director of Edu cationa l Programs, and was supported byth e N A SA Ap ollo-Soyu z Program Office, by Leland J. Casey, AerospaceEng ineer for ASTP, and by Wil l iam D. N ixo n, Educa t iona l ProgramsOff icer , a l l of NASA Headquar te rs in Washington, D.C.


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TeachersAnd Scientific InvestigatorsWho Reviewed the Text

Harold L. Adair, Oak Ridge National Laboratory, Oak Ridge, Tenn.Lynette Aey, Norwi c h Free Ac a de my, N orwi c h , Conn .J. Vernon Ba i ley , NASA Lyndon B . Johnson Space Center, Houston, Tex.Stuart Bowyer, Universi ty of California at Berkeley, Berkeley, Calif .Bill W esley B row n, California State Un iversi ty at Ch ico, Chico, Calif .Ronald J. Bruno, Creighton Preparatory School, Omaha, Nebr.T. F. Budinger, Universi ty of California at Berkeley, Berkeley, Calif .Robert F. Coll ins, Western States Chiropractic College, Port land, Oreg.B. Sue Criswell , Baylor College of Medic ine , Houston, Tex.T. M. Donahue , Univers i ty of Michigan, Ann Arbor , Mich.David W . Eckert , Greater Latrobe Senior High School, Latrobe, Pa.Lyle N. Edge, Blanco High School, Blanco, Tex.Victor B . Eichler, W ichita State Unive rsi ty, W ichita , Kan s.Farouk El-Baz, Sm ithsonian In st i tut io n, W ashington, D.C.D . Jerome Fisher, Emeri tus , Univers i ty of Chicago, Phoenix , Ariz .R. T. Gi u l i, N AS A Lyndon B . Johnson Space Center , Houston, Tex.M . D. Grossi, Sm ithsonian Astrophysical Ob servatory, Cam bridge, M ass.W e ndy Hindin, North Shore Hebrew Academy, Grea t Neck, N.Y.Tim C. Ingoldsby, Westside High School, Omaha, Nebr.Rober t H. Johns , Academy of the New Church, Bryn Athyn, Pa .D. J. Larson, Jr., Grumman Aerospace , Be thpage ,N.Y.M . D . Lind, Rockwell International Science Center, Thousand Oaks, Calif .R. N . Lit t le , U nive rsi ty of Texas, A ustin , Tex.Sarah Manly , Wade Hampton High School , Greenvi l le , S.C.Katherine Mays, Bay City Independent School Distric t , Bay City, Tex.Jane M . Oppenheimer , Bryn M awr Col lege , Bryn M awr, Pa .T . J. Pepin, Un ivers i ty of Wy om ing, Laramie ,Wyo.H. W . Sche ld , N AS A Lyndo n B. Johnson Space Center , Hou ston, Tex.Seth Shulman, Nava l Research Labora tory , Washington, D.C.James W . Skehan, Boston College, Weston, Mass.B. T. Slater, Jr., Texas E duca t ion Ag ency, Aus t in , Tex.Robert S. Snyder , NASA George C . Marshall Space Flight Center, Huntsvi l le , Ala.Jacque l ine D. Spears, Port Jefferson High School, Port Jefferson Sta t ion, N.Y.Robert L. Stewart , M onticel lo High School, Monticel lo, N.Y.Aletha Stone, Fulmore Junio r High School, A ust in , Tex.G. R . T a y lo r , N AS A Lyndon B . Johnson Space Center , Houston, Tex.Jacob I . T rombka , N AS A R obe rt H . Goddard Space Flight Center, Greenbelt , M d.F. O . Vonbun , NAS A R obe r t H . Goddard Space Flight Center, Greenbelt , M d.Douglas W inkle r , Wade H ampton High School, Green vi l le , S.C.


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Contents

Section 1 Introduction ._.. 1V? -. .- -:"/; ,. jSection 2 Obsen&iti$rte of-the tarJh's1 Surface''.-.-.: 3A. Cameras, Lenses, and Filrn 3B. Earth Features and As tronaut Training 5C. Ground Truth 7D. MA -136 Earth Observations Re sults 9E. Quest ions fo r Discussion (Optics , Earth Features,Continental Drift) 19

Section 3 Aerosols That Af fe ct Cl imate and Weather on Earth 21A. Th e Balloon-Borne Dust-Particle Counter 21B. The Laser-Pulse Radar 22C. MA-007 Meas urements and Photographs From Apo llo 24D. Results of MA-007 Measurements 29E. Quest ions fo r Discussion (Climate, Radar, Opt ics) 29Section 4 Oxygen and Nitrogen in the Outer Atm osphere 31A. Layers in the Atmosphere 31B. Spectrum Lines of Atomic Oxygen and Nitrogen 33C. Abs orpt ion by Oxygen and Nitrogen at 222 Kilometers

Alt i tude 36D. MA-059 Oxygen an d Nitrogen Density Measurements 39E. Quest ions fo r Discuss ion (Atmosphe re, Spectrum) 45Appendix A Discussion Topics (Answ ers to Quest ions). 46Appendix B SI Units and Pow ers of 10 49Appendix C Glossary 52Appendix D Further Reading 56

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Figures

Figure 2.1 Storm Clouds West of Mexico Photographed by Apol lo 42.2 The 70-Mi l limeter Hasselblad Ref lex Camera 52.3 Camera Focal Length, Field of V i e w , and Photographic Scale 62.4 Ground-Truth Areas fo r Exper iment MA -136 82.5 Apollo Groundtracks and Earth Observat ion Si tes(a) Western Hemisphere 10(b) Eastern Hemisphere 112.6 The Levantine Rift in Israel 122.7 The Nile River Delta 142.8 The Orinoco River Delta 152.9 Color Di f ference s in the Simpson Desert of Au stra l ia 162.10 Internal Wave s off the Wes tern Coas t of Spain 172.11 Coud Strips off the Coast of Cali fornia 18

Figure 3.1 The Balloon-Borne Dust-Part ic le Counter 223.2 Aero so l Densi ty Versus Alt i tude Over Kansas Ci ty onJuly 22 , 1975 233.3 The Laser-Pulse Radar 243.4 Schematic Diagram of the MA-007 Sunset Measurements 253.5 Photograph and Brightness Contours of the Sun Nearthe Horizon 273.6 Changing Shape of the Sett ing Sun 273.7 The M A-007 Photom eter . 28

Figure 4.1 Temperature and Pressure Versus Alt i tude in the Atmosphere 324.2 Schematic Diagram of Energy Levels 354.3 Emiss ion and Absorpt ion L ines 374.4 Schematic Diagram of MA-059 Lamps and Mirrors 384.5 Motion of Apol lo Around Soyuz at 150 Meters Separat ion 404.6 Motion of Ap ollo Arou nd Soyuz at 500 Meters Sepa rat ion 414.7 Motion of Apol lo Around Soyuz at 1000Meters Separat ion 434.8 Location of MA-059 Experiment Relat ive to the Apol loVeloci ty Vector 44

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1 Introduction

After 4 years of preparation by the U.S. National Aeronautics an d SpaceAdm inist ra tion (NASA ) and the U.S.S .R. Academy of Sciences, th e Apolloan d Soyuz spacecraft were launched on Ju l y 15 , 1975. Two day slater at 16:09Greenwich mean t ime on July 17, after Apollo maneuvered into th e same orbitas Soyuz , the two spacecraft were docked. The astronauts an d cosmonautsthen m et for the first intern ation al hand shake in space, an d each crew enter-tained the other crew (one at a time ) at a meal of typical Am erican or Russianfood. These activities and the physics of reaction motors, orbits around theEarth, and weightlessness (zero-g) are described more fully in Pamphlet I,"The Spacecraft, Their Or bits, and Docking" (EP-133).Thirty-four experim ents were performed wh ile Apollo and Soyuz were inorbit : 23 by astronauts, 6 by cosmonauts , and 5 j o i n t l y . These experiments inspace were selected from 161 proposals from scientists in nin e differentcountries. They ar e listed by numbe r in Pamphlet I, and groups of two or morear e described in detai l in Pamphle ts II through IX (EP-134 through EP-141,respectively). Each experiment w as directed by a Principal Investigator,assisted by several Co-Investigators, and the detailed scientific results havebeen published by N AS A in two reports: the Ap ollo-Soyuz Test ProjectPrel iminary Science Report (NA SA TM X -58173 ) and the Apollo-Soyuz TestProject Summary Science Report (NASA SP-412). The simplified accountsgiven in these pam phlets have been reviewed b y the Principal Investig ators orone of the Co-Invest igators.For man y years, a irplanes have photographed th e Earth's surface. Colorphotographs and special filters have given more and more information aboutthe surfacetemperatures, conditions-of crops and forests , am oun t of waterin th e soil , minerals in exposed rocks, and so on. Start ing in the mid-1960's ,NASA spacecraf t have photographed weather pat terns and detected waterpollut ion, in addit ion to obta ining th e temperature, crop data , moisture,exposed minerals, and so on. From Skylab in 1973, astronauts noted manymore features: wav e condit ions in the ocean, m ajor geologic forma tions, andcondit ions in the upper a tmosphere . It was na t u ra l for the Ap ollo-Soy uz TestProject to extend these observations still fur ther .Apollo and Soyuz were in orbit 222 ki lom eters above the Earth's surface.From this altitude, observation s could be m ade of broad areas of the Earth andof the atmosphere above th e horizon. Although Apollo-Soyuz was abovemost of the Ear th's atmo sphere, there w as some very low density gas even atthat altitude. Three experiments were designed to take advantage of theApol lo-Soyuz view .

Experiment MA-136, Earth Observations and Photography, producedhun dred s of photo graph s, several reels of video tape, and a reel of mov ie film.Ma ny verbal descriptions were also made by the astronauts. The Principal


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Inves t iga to r w as Farouk El-Baz of the Smi thson ian In s t i tu t ion in W a s h i n g t o n .D.C. He was assisted by 12 Co-Inv estigators, who are experts in geolog y,oceanography, and meteorology. They came from various parts of the Un itedStates and one came from India.

Exper iment M A - 0 0 7 , Stratospheric Aerosol Measurement, was directedby T. J . Pepin of the Un ivers i ty of W yom ing. He and seven Co- Inves t iga torsused infrared observations of the sett ing or r ising Sun , as seen from A pollo, tomeasure th e a m o u n t of dus t and droplets in the lower 150 ki lometers of theEarth's atmosphere.

Experiment MA -059, Ultrav iolet Abso rption, measured the densit ies ofatomic oxygen and nitrogen 22 2 ki lometers above th e Earth's surface. T hePrincipal Investigator was T. M. Dona hue of the Univers i ty of M ic h iga n . H ew as assisted by five Co-Investigators.


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2 Observations of theEarth's Surface

Aerial photographs of portions of the Earth are routin ely taken from airplanes,often fo r making maps or surveys. Orbiting spacecraft l ike Apollo-Soyuz orth e earlier Skylab have three main advantages over airplanes as cameramount s . First, th e higher spacecraft can "see" a larger area and can thereforerecord broader features , such as the rema ins of an old volcan o or a huge eddyin the sea. Secon d, the spacecraft is almos t perfectly steady ; there are no gustsof win d or "b um py air" to toss i t around like an airplane, thu s smea ring thephotographs. Third, th e spacecraft follows a precise orbit over a "track" thatruns straight across the ground. A lthou gh the spacecraft moves m uc h morerapidly than an airplane, modern cameras are fast and some are bui l t tocompensate for the spacecraft velocity.

Farouk El-Baz, the Pr incipal Invest iga tor fo r E x p e r i m e n t M A - 1 3 6 ,strongly favors astronauts ' visua l observations wit h "backup" photography .He points out several cases where astronauts glimpsed features that did notshow up on the photographs, and other cases w here astronauts chose the t imew h en th e l i g h t in g w as just r ight to take photographs that would show what th eastronauts were seeing.

The Earth observations were carefu lly planned to provide inform ationneeded by geologists for studies of m ounta ins, r ivers, deserts, and cont inenta ldrift. Other information helped oceanographers to study sea currents andmeteorologists to study tropical storms and hurricanes (Fig. 2.1) . Most ofthese studies provide direct b enefits to us ground-based residents on E arth.

A Cameras, Lenses, and FilmOne objective of Experiment MA -136 w as to check the effectiven ess ofdifferent cameras fo r photographing various features from orbit . Five ca merasan d seven different lenses were provided on Apollo. The largest cam era w as aHasselblad reflex (Swiss built , see Fig . 2 .2) , wi th 70-mil limeter f i lm and twolenses, one wi th a focal length of 250 mill im eters and the other of 50mil l imeters . The focal length of the lens determines the size or scale of thephotograp h: the larger the focal leng th, the greater the enlargem ent (Fig. 2.3).T he field of view, however , is larger (o n 70-mil l imeter fi lm) whe n th e shorterlens is used. The 50-mill imeter lens was used for wide-angle views, and the250-mi l l imeter lens w as used fo r large-scale, h igh-resolu tion photograph s.

An other Hasselblad camera had 60- and 1 00-m ill imeter lenses and wasmou nted f irmly on a bracket to take mapping photographs thro ugh one Apollow i n d o w . This camera had an "intervalometer" to t ime the exposures so thateach photograph overlapped the preceding one by 60 percent. Every pointalong the groundtrack w as thus photographed at least twic e, once from each oftwo points in Apollo's orbit several hundred kilometers apart. Pairs of these


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overlapp ing photographs y ie ld ste reoscopic v iew s f rom w hich t ra inedspecialists can "interpret" such information as he i gh t s of c louds and m o u n -tains and depths of canyons .

Figure 2.1 This photograph of an unusual cloud system was taken along the westerncoast of Mexico looking westward over the Gulf of California. The land in thebackground is Baja California.

J E M AL PAGE Lf:OF BOOR QUAJUrrv


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The 70-millimeter Hasselblad reflex camera system. Figure 2.2

There were tw o smaller cameras: a 35-m i l limeter Nikon s ingle - lens re f lexcamera with a 55-m ill imeter focal-len gth lens (Japanese) and a 16-mill imeterMa ue r mov i e cam e ra (American) . There w as also a t e levis ion camera fo rreal-t ime broadcasts f rom Apollo-Soyuz and a video tape recorder to recordtelevision views of the Pacific Ocean. The color film used in the cameras w asspecial ly prepared for the MA-136 Experiment by Eastman Kodak. A specialcoating w as used on the emuls ion to preven t halat ion by blue l ight . (Halat ionis the unrealist ic haze around a bright object in a pho togr aph .) More than 1900photographs w ere taken from Apol lo for the MA -136 E xper iment ; 75 percentof them are of exce l lent qua l i ty .

D Earth Features and Astronaut TrainingExcept fo r photographs from orbi t , w e people on the ground never get a clearview of large Earth features. A fami l ia r example is the satel l i te weatherphotograph shown on te levis ion wea ther newscas ts , which revea ls wea ther

ORIGINAL PAGE IBOF POOR QUALITY


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Light from ci ty on Earth/

Edge

Lens Camera

Light from ci ty on Ear th

Edge Edge

T

imengthII0-mmfocal length11 -m m image of50-km c i ty

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16

57-mm image of50-km c i t y- 70- m m

Figure 2.3 Camera focal length, fieldof view, andphotographic scale.


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fronts an d storm centers fa r better than any view of the clouds from Ear th .Oceanographers plot maps of water currents over small areas, a little bit at at i me . Ho wev er, satelli te vie ws of the Gulf Stream along the East Coast of theUnited States show vivid color contrasts between the colder Atlantic wateran d th e giant eddies in the Gu lf Stream near islands and reefs. Geologists alsoplot small-scale evidenc e of rifts or fault l ines on maps, but they do not alwaysrecognize th e full ex ten t of these features. Rif ts and faults are huge cracks inth e Earth 's crust where th e rock on one side has slipped past th e rock on theother side. The slip can be u p - d o wn or sideward. The most famous slippage inth e United States is the San Andreas Fau l t , which runs nor th- to -sou th inCalifornia and is easy to see on satellite photographs.

These topics were discussed in science classes for the astronauts 60 hoursof classroom t imedur ing th e year before th e Apol lo-Soyuz miss ion . T heas t ronauts also had 10 "f lyover exercises" d u r in g wh ich th ey flew inairplanes over faul ts , sea eddies, and desert dunes . They learned how todescribe a fault l ine on a tape recorder and how to judge th e color of seawateror desert sand by using a ' 'color wh ee l . ' ' T he color wheel onboard Apollo had54 redd ish-brown colors and 54 blu ish-gre en colors on a paper disk . Theas t ronauts selected the color most similar to the seawater or desert sand thatthey observed an d tape-recorded the color-wheel nu m ber . These color nu m -bers were imp ortan t because the color photogra phs mi g h t be underexposed oroverexposed and not show the actual colors.During the aircraft f lyover exercises, th e ast ronauts exper imented w i thseveral pairs of binoculars and f inal ly selected an X 16-power monocular fo ruse on the Apol lo-Soyuz f l ight. This little telescope enlarged w hat they sawbelow and helped them to identify fea tures to report or photograph.T he purpose of all th is t ra in ing was to help th e Apol lo as t ronautsTomStafford, Deke Slay ton , and Van ce B r an d b eco m e we l l - in fo r m ed in geol-ogy , oceanography , and meteorology so that t h ey wo u ld qu ic k ly recognizefeatures of scientif ic importance.

Ground TruthThe P rincipal In vestig ator had cons ulted a group of 42 experts to decide wh atEarth fea tures th e astronauts should look for and photograph. Some of theseexperts were able to have measurements made on the Earth 's surface to verifywhat w as seen or photographed from Ap o l lo - So y u z . F or ins tanc e , severa lgroups of sh ips measured sea-sur face tempera tures , salinity (thea m o u n t ofsalt in the water) , water color , red t ides (po isonous p la nk to n in the wate r ) ,water cu r r en t s , w i n d v e lo c i ty , and cloud types. Figure 2.4 sh o ws the 18 areaswhere such "ground-truth" mea surem ents were made w hi le Apol lo -Soyuz


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Figure 2.4 Locations of ground-truth teams for Experiment M A - 1 36, Earth Observationsand Photography.

O Airc ra f t supportD Oceanography supportA Ground support

ISRO - Indian Space Research Organization(aircraf t support)


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passed overhead. Tw o airplanes flew across th e U n i t e d States and tookphotographs from high alt i tudes to compare w i th t h e MA- 1 36 m ap p in gphotographs taken at the same time; several other airplanes did the same nearN ew Zealand and England. A team of Egyptian geologists mapped a portionof the Western Desert of Egypt, which was photographed twice by Apollo-Soyuz.

In every case, th e MA-136 observations agreed wi th th e local ground-truthdata, even thoug h the MA -136 da ta extended over muc h larger areas. Some ofthe ground-truth sites were covered by clouds whe n Apollo passed, amon gthem the si te of the New England red t ide off the coast of Maine. (Theast ronauts v iewe d re d wa ter far ther north in the Bay of F u n d y but reported it tobe redd ish-brown muddy water from rivers, not the bright-red color of theplankton in the red t ide.)

P) MA-136 Earth Observations ResultsThe numerous color photographs and astronaut reports wil l be studied foryears. Several important discoveries ha ve already been made from t h em , an dmore may yet be found . Figure 2.5 shows the locations of the visu al obse rva-tions, the photographic mapping observations, and the television video taperecordings. Each num bered area (1 to 12) concerned a specific scientif icprob lem. For ins tance , area 11 is the h u g e A N Z U S E d d y ( fo r /4us t r a l ia - /VewZealand-t /nited States) off the eastern coast of Aust ra l ia , and area 9 sh o ws th egrowing deserts of North Africa.One important discovery is shown in Figure 2.6, a photograph of theLevant ine Rif t . F or years, scientists had know n about th is huge crack in theEar th ' s c rust ; however , the A pol lo -Soyuz M A-13 6 Exper im ent revealed i t sfull ex ten t . The rift ex tends from th e G u l f of A q a b a ( a t th e northern end of theRed Sea) north wa rd throu gh the Dead Sea to the Sea of Galilee in Israel,where it spli ts into three crack s that fan out to the north an d nor theast . The riftis probably caused by the counterc lockwise drift of the Ar ab ian peninsu la(away from Afr ica) around a "pivot" near the Sea of Galilee, wh ere the riftsplits. Geologists find more and more ev idence tha t en t i re co nt ine nts have"drifted" dur ing man y m il l ions o f years . For ins tance , Nor th and SouthAmerica seem to have drif ted very slowly away from Europe and Afr ica ,leaving a basin ( the A tlant ic Ocean) in betw een. Alo ng the eastern coast ofSouth America , th e types and ages of rocks (and th e fossils in t h em ) m a tchthose along the w estern coast of A frica, and the outlines of these two coasts f it


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Figure 2.5 Maps showing the broad locations of the MA-136 Earth observation sites.Small circled numbers represent revolution groundtracks for photographicmapping and visual observation tasks; large circled numbers represent theEarth observation sites.

v isua l observat ionsMapping an d visual observat ionsTelevision i i60

165 180 165 150 135 120 105

Longitude(a) Western Hemisphere.

90 75 60 45 30

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Legend:Visual observat ionsMapping an d visual observat ions

60

75 90 105 120 135 150

(b) Eastern Hemsphere.

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Figure 2.6 The southern part of the Levantine Rift, extending from the Dead Sea to theSea of Galilee, is distinguished by the linearity of the Jordan River valley (ar-row). To the north, a "fan-shaped" complex system of curved faults character-izes the rift. One prominent fault parallels the Syrian coast and then makesanoticeable bend to the northwest (arrow) towards Turkey.


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together like pieces of a jigsaw puzzle. The theory of "cont inental drift" or"plate tectonics" is a complicated subject.1 Geologists are looking fo r moreevidence for the theory on MA-1 36 photographs.

A more rapidly changing feature, th e delta of the Nile River , is sh o wn inFigure 2.7. T he Nile River f lows nor thward from Egypt in to th e Mediterra-nean Sea. M ud from th e Nile has slowly formed th e del ta , and the fresh waterof the Nile can be seen in Figure 2.7 mi xing with the salt ier wate r of theMediterranean offshore. The delta of the Orinoco River in Venezuela isshown in Figure 2.8 . Muddy r iver water can be traced fo r hundreds ofkilometers out into the Caribbean Sea and the Atlantic Ocean.The colors of desert sands, such as those show n in the photograph in Figure2.9, provide important information about th e ages of these sands and theadvance of deserts across the countryside. The bright-yellow sand is youn gerthan the red sand. The sharp line to the left of the center of the photographshows where the yellow sand is moving across the red sand as i t is blownwestward by winds. Differences between this Apollo-Soyuz photograph andSkylab photographs taken in 1973 wil l show th e rate of advance. The chang-in g pattern of the sand dunes is also being studied.Photographs of Lake Chad, at the southern edge of the Sahara, show thesand mo ving in toward the lake. T his advance of the desert m ay dry up LakeChad and deprive th e local inhabitants of water to dr ink and fish to catch .Other deserts were photographed in Austra l ia and Argent ina .A view of western Spain, including th e Strait of Gibra l tar , is s h o w n inFigure 2.10, which was photographed w h e n the astronauts saw a series ofwa ve s about 60 kilometers long in the otherwise clear blue Atlantic Ocean.These waves are not on the surface but are deep in the water below. They m ayhave formed because of variations in the salinity (salt iness) of the watercaused by salt ier water pouring out of the Mediter ranean Sea t h r o u g h th eStrai t . T he waves were glimpsed only for a m o m en t wh en th e l igh t ing ( "Sunglitter") w as just r ight. They could be seen then because l ight is refractedmore by the salt ier water .

Several of the mapping runs (Fig. 2.5) covered areas that had not beenaccurately mapped before. O ne photograph revealed an ancient meteor craterin Brazil . Others showed snow conditions in the Cascade Mounta ins an dglaciers in other parts of the world. Two tropical storms in the Caribbean Seaand off the coast of Florida and m a n y cloud patterns over land and sea werephotographed. O ne peculiar set of cloud strips is shown in Fig u r e 2 .1 1 . N o

'ESCP, Sees. 1 1 - 1 1 , 1 1 - 1 2 . (Throughou t this pamp hle t , re fe rences wil l be given to key topicscovered in these three standar d textbooks: " Inv esti gat ing th e Earth" (ESC P) , Houghton Miffl inC ompany , 1973; "Phys ica l Science Study Commit tee" (PSSC), four th edi t ion , D. C. Heath ,1976; and "Project Physics," second edition. Holt , Rinehart and Wins ton , 1975 . )

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Figure 2.7 The Nile Delta is an excellent example of a triangular-shaped delta. Patterns ofsurface texture and boundary layers in the water are easily seen in the Sun'sreflection. They possibly result from a density difference between the fresh-water from the Nile and the saltier water of the Mediterranean Sea. Comparethis photograph with a map of Egypt.

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.,


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The deep-brown color of the Orinoco River outflow is caused by both sedi-ments (mud) and rotting plant material. This turbid water was observed by thecrew as far north as the island of Barbados.Figure 2.8

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Figure 2.9 There is a color gradient in this downward view of the Simpson Desert inAustralia. The long, thin, linear dunes of sand were described by the Apollocrew as "hundreds of parallel road tracks." Such dunes form in bare, sandyareas where the winds come predominantly from one direction. The lines ofdunes are perpendicular to this direction.

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The direction of sunlight in this photograph has made internal waves visible(lower left). Locatedoff the western coast of Spain, the waves were approx-imately 50 to 60 kilometers long and were probably caused by variations insalinity.

Figure 2.10

'*

Atlantic Ocean


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Figure 2.11 Cloud strips off the coast of California.

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one understands how they were formed. They are too large to be airplanecontrails (streaks of condensed water vapor left behind airplanes f lyingthrough hu m id air) , many of w hic h were observed over the Atlantic Ocean.

Questions for Discussion(Optics, Earth Features, Continental Drift)

1. The normal human eye can resolve 2 (separate) tw o objects 0.02 apart;that is , you can see separately tw o l ines 0.03 mill im eter apart on a paper that is10 centimeters from your eyes. How far apart wou ld two r ivers have to be forthe astronauts to see them separately from 220 kilometers alt i tude? H ow closecould the rivers be if the astrona ut used his mon ocular to see them separately?

2. Apollo-Soyuz had an orbital speed of 7.4 km/sec . The Hasselbladmapping camera with a 100-mill imeter lens had a field of view of 38. Toobtain a 60-percent overlap of successive photographs, wh at interva l betweenexposures would be necessary? If the 60-mill imeter lens were used, w ould th einterval be shorter or longer?

3 . Which camera- lens combinat ion would you use to get the best resolu-tion of Earth features?

4. If you were an astronaut describing th e view sh o wn in Figure 2.6, whataspects would you emphasize? Remem ber tha t you are m o v in g at 7.4 km/sec ,so your view lasts only a m in u te or two.

5. A ground-truth team is being sent to the desert shown in Figure 2.9.What measurements would you ask them to make?6. The Amer ican cont inents are drif t ing away from Europe and Africa at a

rate of about 2 cm /y r . H ow long ago were they together? (Geologists call th eor ig inal landmassNorth and South Amer ica , Europe, Afr ica , Asia, andAustralia"Pangaea." T he southern portion w as "Gondwanaland.")

2PSSC, Sec. 8-8.

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3 Aerosols That AffectClimate and Weatheron EarthAerosols are small droplets and dust particles suspen ded in the air. They arecarried to alt i tudes of 20 to 30 kilom eters by wind s and atmospheric circula-t ion. The ir absorption and scattering of sun ligh t affec ts the climate and (at lowaltitudes) th e we ather . Experim ent MA -007, Stratospheric Aerosol M eas-ure me nt , used three methods to measure th e size, type, and am o u n t ofaerosols at high alt i tudes: (1 ) counts of particles by microscope detectorscarr ied in a high-alt i tude balloon, (2) measure me nts of l ight scattered backfrom laser pulses directed u p throug h the atmosphere, and (3) measure men tsof the Sun's brightness as it rose or set, as seen from Apollo-Soyuz. The firsttw o ground-based methods covered alt i tudes up to 25 to 30 kilometers atabout the same time and in the same area that Apollo-Soyuz observations werebeing made at alt i tudes up to 45 to 50 kilometers. The experiment dem-onstrated that th e spacecraft technique is accurate an d tha t it wi l l be useful fo rdetermining the am o u n t of aerosols at high alt i tudes. (Aerosol spray cansproduce th e same k ind of droplets as those detected in Exper iment MA-007 . I tis not these droplets how ever, that may reduce the ozone layer; i t is the Freongas used in the spray cans. This gas slowly rises through th e atmosphere, andsome scientists fear that it s f luorine and chlorine m ay cause chemical reac-tions in the ozone layer . See Figure 4.1.)

A The Balloon-Borne Dust-Particle CounterBalloon f l ights are made regularly from a U.S . Air Force base near KansasCity, Missouri . O ne flight w as scheduled at the same time that aerosolobservations were being made from Apollo at sunset at 01:38 Greenwichmean t ime (GMT ) over Kansas Ci ty on July 22, 1975. A cutaw ay draw ing ofth e particle counter carried on these balloon flights is shown in Figure 3.1. Astream of outside air is pumped through a concentrated l ight beam, and twomicroscopes are focused on this point. When an aerosol droplet or dustparticle passes through, a bright flash is recorded in each microscope by aphotomul t ip l ie r at the eye end of the microscope. I f both photomul t ip l iersgive an electric pulse at the same instant, a "count" is recorded by theelectronic circuit . This me chanism is a "coincidence counter" (see PamphletII) ; i t uses two detectors to eliminate false counts. (A false count could berecorded by one detector if a cosmic ray passed through the pho tom ultiplie r .Another check of false "background" counts was made by f i l ter ing theairstream fo r short interva ls every 15 minutes. During these intervals, thereshould have been no coun ts, and there were none except at very low alt i tudes.)

The pulse size of the photomul t ip l iers shows how large th e droplet or dustparticle is simply because a larger particle reflects more l ig ht. The electron icswere arranged to separately record th e particles of 0.3- to 0.5-mi.crometer

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diameter (small pulses) and the large particles (large pulses). (One microme-ter is only 0.00004 i n ch . ) T he particle counts were radioed to the ground ,together w ith the tem perature and pressure at each a lt i tude, and were recordedas a funct ion of t ime. These records show hig h concentrations of aerosols upto 5 kilometers (16 000 feet) , then a sharp drop to about 1 particle/cm 3 . Therewas a ma xim um of about 60 particles/cm3 at 18 kilometers alt i tud e. Above 25ki lometers , th e particle count w as back down to 1 or 2 particles/cm 3 (seedashed line in Fig. 3.2).

Photomult ipl iers

Exhaust

(Light)

Figure 3.1 Schematic drawing of the University of Wyoming dust-particle counter usedfor ground-truthmeasurements.

P TheLaser-Pulse RadarThe "lidar" sh o wn in Figure 3.3 is a 122-centimeter (48-inch) telescopeloaned by the N AS A Langley Research Center for the MA -007 Exper im ent .A pow erful laser is m o u n ted at the telescope focus and gives extremely shortpulses of 30 nanoseconds' dura tion. A flash of l ight leaves the telescope,travels up through the nighttim e atmosphere, and is scattered back toward the

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Earth by dust and aerosols. The scattered l ight is collected by anothertelescope and focused on a sensitive detector. The velocity of l ight is k n o w n ;therefore, the altitude of the dus t and aerosols can be calculated from th eround-tr ip t ime (160 microseconds for an al t i tude of 24 kilometers). Thedifference in color (wav elength ) between th e scattered l ight and the laser lightis also recorded; it is used to obtain info rm atio n about the particles, such assize and refractive index.The lidar was set up at the U.S.A ir Force base near Kansas City and usedth e night before and the night after th e observations from Apollo-Soyuz werem ade . O n July 22, the lidar recorded some cirrus clouds at 13 kilometersaltitude, as well as aerosols around 20 kilom eters. On July 23, there w ere nohigh clouds, and the aerosols again were detected at 20 kilometers.

30

MA-007 measurements

20

10

Bal loon meas urements

f

1 0 > 10"" 10-Aerosol densi ty

Aerosol density versus altitude over Kansas City on July 22, 1975. Figure 3.2

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\Figure 3.3 The NASA Langley Reserch Center 122-centimeter lidar system. It can beused to measure distances to clouds, balloons, and airplanes, as well as toaerosols.

Q MA-007 Measurementsand Photographs FromApolloWhen l ight passes thro ugh the atmosph ere, some of i t is absorbed an dscattered by aerosols an d some of it is scattered by the air molec ules to give theblue light of the sky.The atmosphere also bends rays of l ight , as shown inFigure 3.4. This bending ( " r e f r ac t ion" ) is caused by the increase in airdensi ty at lower al t i tudes. The l ight t ravels sl ightly slower in the denser airand its direction is changed, much l ike the way a car veers to the r ight when it s

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Apollo-Soyuz DibitObser va t ionsf romApol io

Schematic diagram of MA-007 sunset observations. (The layers of the at- Figure 3.4mosphere and the Apollo-Soyuz orbit are exaggerated for clarity.)

r ight wheels get into sof t mud beside the road and its left wh eels are st i l l onsmooth pavem ent . Light f rom the se t t ing Sun i s thus bent dow nw ard l ike thera y to point 4 in Figure 3.4, and the Sun looks h ighe r in the sky than it really is.This refract ion by the atmosphere is similar to refract ion by a glass prism . Thedense air low in the atmosphere is like th e th ick end of the pr i sm. I t slows th el ight more than does the less dense air a t higher al t i tudes, w hich correspondsto the th in end of the prism. Just before sunset , the l ight reaching Apollo atpoint 4 passed through air in layer A very close to the Earth's surface, asshown by the arrow. This l ight was affected by aerosols at low al t i tude.Ear l ie r , l ight passed through higher a l t i tude air to reach point 3. The M A - 0 0 7Experimen t used m easurem ents of the Sun ' s br ightness for 1 .5 min utes beforesunset to es t imate the am ount of aerosols in layers A, B, C, D, and so on. O fcourse, th e sunl ight received at po i n t 4 passed th roug h layers B, C, and D aswell as l ayer A, so the ca lcula t ion is compl ica ted .

The refract ion of the sunl ight (bending toward Ear th in Fig. 3.4) dependson the change of a ir densi ty with al t i tude. The MA-007 scientists measuredth e refract ion on photographs of the Sun taken w i t h the Hasselblad 70-m i l l im e te r camera (Sec. 2A) u sing the 250 -mill im eter lens, an infrared f i l ter ,and spec ia l infrared f i lm tha t recorded l ight of 8400-angs t rom (840-nanom eter) wave len gth. This gave a sharper photograph than ordinary v is ib le

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l igh t wo uld have because m uc h of the l ight scattered by aerosols w as filteredou t . F ig ure s3 .5(a )an d3 .5(b ) show one of these photographs and the contoursof br ightness measured on it. The Sun near th e horizon appears to be f la ttenedbecause the rays near the h orizon (from the bo ttom of the Su n) are refractedmore than th e rays farther up (from the top of the Su n) . This makes th e bottomseem farther up, as s h o w n by the ray to po i n t 4 in Figure 3.4. Fig ure 3.5(c)shows th e apparent shape of the Sun expected from refract ion; i t matchesFigure 3.5(b) we l l . F igure 3 .6 shows the apparent ly chan ging shape of theSun in the last 15 seconds before sun set . (The Sun set mu c h more qu i c k l y asseen from Apollo than as seen from the ground because the spacecraft had a"day" of on l y 93 minutes ins tead of our 24 hours . )

The S un ' s changing br ightness was measured for 1 .5 m inutes before sunse tw i t h th e MA-007 photometer shown in Figure 3.7. This ins t rument w as a imedat the Sun t h rough a w i n d o w in the Apol lo Command Module (CM) cabin. I twas a pinhole camera w i th a f i l tered phototube that recorded th e intensity of8400-angstrom l ight from a 10 field of v i e w. The Sun is only 0.5 indiameter, so the spacecraf t did not have to be pointed very accurately. Theas t ronau t s could check th e po i n t i ng by the shadow of a pin on a w hi t e circle(top of Fig. 3.7).The ph otom eter ' s 1 .5-m inute record of changing Sun br ightness wasradioed to the ground and later converted to curves of aerosol den si ty versusa l t i tude . T he c u rve fo r sunse t over Kansas Ci ty is s h o w n in Figure 3 .2 , w herethe dashed l ine show s the balloon m easure me nts. The agree me nt is good from17 to 23 ki lome ters a l t i tude . The MA-007 Experiment shows more aerosols athigher a l t i tudes .

One of the Soviet experiments on Apollo-Soyuz was very similar to theMA-007 photography. As ment ioned in Pamphle t I , the cosmonauts per-formed si x exper iments on t he i r own in addi t ion to the five jo int exper im ents .One of the jo int exper iments was the Artif ic ial Solar Ecl ipse (MA-148; seePamph let I II) for which A pollo blocked (ecl ipsed) the Sun as seen fromSoyuz. The cosmonauts la ter used the camera from that experiment to photo-graph th e set t ing Sun and the stars seen near th e S un . B y me a su r i ng th e S u n ' sshape and the distances between th e stars in the sky, th e refract ion at differental t i tudes was obtained. In this way, the air densi ty at various al t i tudes wasdeterm ined. The U .S .S .R . has not yet released the results of these experi-ments . In another exper iment , th e cosmonau ts cont inued photography aftersunset to measu re the zodiacal l igh t (Pam phlet III) , and they photographed thehorizon in other direct ions to detect "airglow." (Yo u can see the airglow as ablue haze above the horizon at the top of Figure 2.1 and on the photog raph onthe cover . )

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Images of the Sun. Figure 3.5

(a) Photograph of the Sunnear the horizon. (b) Contours of imagebrightness in (a).

(c) Expected shape of the Sun'simage due to refraction.

10 12.5 15 1752.5

The shape of the setting Sun appears to change because of refraction by the Figure 3.6atmosphere.

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Figure 3.7 The photometer used for making stratospheric aerosol measurementsfor Ex-periment MA-007.

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D

E

Results of MA-007 MeasurementsT he Stratospheric Aerosol Measu r em en t Ex p er im en t on Apol lo-Soyuzshowed that a fairly simple 7-kilogram instrum ent (the photometer show n inFig. 3.7) can check high-altitude aerosol densities in short observation timesbefore sunset and after sunrise on Earth-orbiting spacecraft. In addition to thesunset over Kansas City, one other sunset off the coast of New Jersey and twosunrises, one northwest of Australia and the other over th e Ind ian Ocean, wereobserved . The two sunrise observations sho wed 3 0-percent fe we r high-alt i tude aerosols in the Southern Hemisphere than in the Northern Hemi-sphere.Why should aerosol densities be so different in the two hemispheres?Scientists attribute th e difference to a volcano that erupted in Guatemaladuring October 1974, 9 mo nths before th e Apollo-Soyuz mission. During th enorthern winter , there is a general northward movement of the atmospherew h i c h , in this case, carried the volcanic dust and droplets at least 2400kilometers (1500 miles) north to Missouri and New Jersey. Later , during th esouthern winter (northern sum mer), the aerosols probably moved south wa rd.

Combining the balloon data on droplet or particle size, the lidar data on thecolor of backscattered light, and the Apollo MA-007 data on alt i tude gives anestimated 1.43 for the index of refraction of the aerosol d roplets . (Thisrefraction is not in the atmosphere but in the droplet.) The MA-007 scientistsnote that this somewhat uncertain num ber is consistent w ith the droplets beingsulfuric acid (75-percent H,SO4 and 25-percent P ^O), wh ich possibly re-sulted from th e release of hydrogen sulfide ( I - L ^ S ) an d sulfur dioxide (SO 2)from th e volcano and the subsequent combining of these compounds wi thoxygen and water in the atmosphere.

Questions for Discussion(Climate, Radar, Optics)

7. If the aerosol particles in the entire atmosp here were increased by afactor of 10, how would you expect the climate on Earth to be affected?

8. In order to plot th e n u m b er of aerosol particles per cubic cent imeterversus th e al t i tude in kilometers, what do you need to know in addition to theballoon-borne dust-particle counts?

9. W ith i ts 30-nanosecond pulses, how a ccurate can the l idar mea sure-m en t of aerosol altitude be?

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10. In the atmosphere, different wavelengths are refracted by differentamounts (Fig. 3.4). How would this change photographs of the setting Sun inwhite light (such as Fig. 3.5(a))?

11. How large was the image of the Sun on the original 70-millimeter filmin the Hasselblad camera with the 250-millimeter lens?

12. Two successive sunsets from Apollo-Soyuz were 93 minutes apart int ime. If the first was over Kansas City (95 W longitude), at what longitudewould yo u expect th e second?

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gas. However , th e temperature starts rising again above th e "mesopause" atabout 90 kilometers a lt i tude. This outer , very low de nsity laye r is called thethermosphere because it is very hot, as measured by the average velocities ofatoms and mo lecules. At the alt i tude of Apollo-Soyuz (222 kilometers) , thegas temperature is about 780 K (507 C). Information about the ionosphereabove 120 kilometers comes mostly from spacecraft and rocket measure-men ts. The pressure and the density keep fall ing, wh ich causes the tempera-ture to r ise, and the composition ch anges (re lative ly more h ydrogen andhelium see Pam phlet III) . The outermost layer , called the geocorona, ismost ly hydrogen and ex tends ou tward 50 000 k i lometers , where i t mergeswith th e very lo w densi ty hydrogen and hel ium between th e planets . In thelow-den sity regions, inform ation about composition can be obtained byobserving the l ight emitted or absorbed by the gas, as revealed by absorptionand emission l ines in the spectrum.

Spectrum Lines of Atomic Oxygen andNitrogenGases can em it various colors of l ight , and this property is used in neon signsfo r adve rtising. Pure neon radiates a characterist ic red l ight whe n exci ted by adischarge in a sealed glass tube, and other gases at low pressure emit othercolors. A spectroscope shows "emission lines" in the spectrum (seePam p h le t s II and III) ; that is, the in tens i ty is strong in a n u m b e r of narrowbands of wav elength (color) , and the pattern of brig ht l ines is characterist ic ofth e em it t ing gas. W hen l igh t from a distant source passes through th e samegas, m ost of the same w ave len gth s are absorbed by the gas, leaving gaps, o r"absorption lines," in the same p attern. 3 The more gas there is along the l ineof s ight , th e darker th e absorption l ines. Scientists measure these l ines with aspectrometer , w hich separates th e different wav e len g th s A and measures th ein tens i ty /^ a t each w avelen gth . Ast ronomers use the measured wav eleng thsof spect rum l ines to ident i fy gases in interstellar space and to estimate th ea m o u n t of each gas in terms of the n u m b er s of atoms or molecules along th el ine of sight.

'Project Phys ics , Sees. 19.1, 19.7, 19.8; PSSC, Sees. 26-2 to 26-5.

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The spectrum lines 4 (both emission and absorption) were explained byquantum theory in terms of electrons in orbit around the nucleus of an atom.Each orbit has a different energy. According to quantum theory, only certainspecific orbits are "permitted," with energiesE,, E2, E3, and so on. These' 'energy levels'' are different fo r each kind of atom. T he spectrum lines comefrom "electron jumps" between energy levels, downward fo r emission linesand upward for absorption l ines. In a downward jump, the atom emits aphoton. If the electron jumps from E 2 to E l, the photon has energy 2 E t =hf = / ic/X, whe re h is the Planck constant,/is the photon fre quen cy, and c is thevelocity of l ight. So, all the jumps f rom 2 to E l give photons of the samewavelength \. Different kinds of atoms have different ,, E2, E3, and so onand thus emit photons of different wave lengths . This pa t tern of wavelengths inthe spectrum is often called the "finge rprint of the atom" because it is uniq ueto one kind of a tom.The pattern of absorption lines is the same "fingerprint" because that onekindof atom absorbs photons of energy E2 -E, wh en it jumps f rom E1 to E2and photons of energy E3 - E, wh en it j u m p s from E, to E3. These are thesame energy differencesphoton wavelengthsas for the emission l ines.Thu s, the fin gerp rint of the atom is the same in absorption lines as in emissionlines, with a few exceptions as noted below. Figure 4.2 is a diagram ofenergy levels with th e downward (emission) and upward (absorption) jumpsmarked with arrows. For most atoms, the energy levels must be arranged incolumns (not shown in Fig. 4.2) , and there are "selection rules" aboutwhich jumps are most probable between levels in the various columns.T he lowest energy level, E I; is called th e "ground state," and each atomprefers to be in that state. If an atom absorbs a photon or is jogg led into ahigher energy level by high temperature or by collision, it can emit a photonand return to, almost instantan eously. In the cold dark of interstellar space,most atoms are in theE t level, so the j u m p f r o m E , toE2 (which occurs wh en aphoton is absorbed, thereby removing i t from the light beam) gives a strongabsorption line, called the resonance l ine for that atom . The same wa velen gthwil l be em itted later because th e atom "prefers" to be in the lowest energyground state. This reemission or "resonance scatter ing ' ' does no t "fill in ' ' th eabsorption line because th e emitted photons go off in all different directions,not just along the l ight beam from which photons were first absorbed.

In th e laboratory, phy sicists have m easured th e probabi l i t ies fo r absorptionor emission of a photon by each kind of atom and the p robab ili ty for eachenergy jump. If 100 atoms are in the level E 3 in Figure 4.2, the physicists


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t..

line.

,

ce*. .

Downwardjumps giv ngemission ines

,

(Morejumpsto an dfromhighers ta les)

/ (More s ta te s ), ; 1

t

'

'Resonance* line

Upwardumps g vingabsorp t on ines

Schematic diagram of energy levels in one kind of atom and jumps giving Figure 4.2spectrum lines. (The larger jumps correspond to shorter wavelengths.)

know tha t 20 of them wi l l jump to E 2 and 80 to ,, in less than a micro-second. If 100 atoms are in level , w ith ma ny photons passing them (i ns t rong sunl ight , fo r instance), 7 0 wi l l j um p to2, 20 to3, 5 to 4, and 5 toother higher levels. (These num bers are cited for illustration on ly. In actu ality ,there ar e many bi l l ions o f atoms, and the jump probabi l i ty is not an evenpercentage l ike 80 percent . The point is that these probabil i ty numbers areknown fo r most kinds of a toms and the resonance lines are the most probablel ines for each kind of atom.) Therefore, one can calculate f rom the inten si ty ofthe2 - , emission-l ine strength how many a toms in the l ine of sight werein the 2 level . The , - 2 absorption line w ill give the n u m b e r of atomsin the line of sight that were in the , grou nd state .

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A complete and accurate diagram of energy levels for an a tom l ike oxygenis more complicated than the one shown in Figure 4.2. Som e 80 years ago,physicis ts f ound tha t some energy jumps did not take place , an d they calledthese jum ps " forbidden t rans i t ions ." When th e energy levels were plot ted inseparate columns, i t was possible to make "se lect ion rules" s ta t ing wh icht ransi t ions were "permitted" and whi c h we re "forbidden," all keyed to a setof three qua ntu m numb ers associated w i t h each energy level . Then astron-omers found some of the "forbidden lines" in the spectra of nebulaevastc louds of low-dens i ty , g lowing gas be tween the stars. They are still called"forbidden lines," a l thoug h the q u a n t u m theory now shows that a "forbiddenj u m p " from level Er to E, is not real ly impossible bu t just very improbable.T he atom waits for a second or two in level Er be fo re j um pi n g to E l. U n d e rmost cond it ions, the atom is bombarded man y m il l ion s of t imes du rin g asecond and gets joggled out of Er before th e f o rb i dden j um p can take place.That i s why 19th-century phys ic i s t s never observed forbidden l ines in t he i rlaboratories.In very lo w density gas near the top of the Earth ' s atmosphere and innebulae between th e stars, an atom may not be jost led out of level Er beforej u m p i n g to , and emi t t ing the forbidden l ine . The aurora (northern l igh ts )and nebu lae most ly g low in forbidden l ines of o x y g e n . T he a t oms of oxyge nare raised to the energy leve l Vby sola r-wind bombardm ent , and the oxygenions (O + + ) in ne bu l a e get to their energy leve l E f b y s imi la r e lec tronbomba rdme nt . T he absorption of a forbidden l ine is possible but veryi mp ro b ab l e , so we do not expect forb idden absorption l ines.

A resonance l ine of atomic oxyg en at a wa vele ng th of 1304 angstrom s(130.4 n anom eters ) and a forbidden line of oxygen at 1356 angstroms (135.6nanometers ) are shown in Figure 4.3. Both l ines ar e produced by a h i gh-vol tage radiof requency oxygen lamp. However , when l i gh t passes t h roughatom ic-oxy gen gas, only the 1304-angstrom l ine is absorbed. The same ist rue for ni t rogen wi th th e resonance line at 1200 angs t roms (120 nanometers )and the forbidden l ine at 1493 angstroms (149.3 nan om eters) (Fig. 4.3). Ani t rogen lamp produces both l ines but on l y th e 1200-angstrom l ine is absorbedby ni t rogen a toms. These wa ve l e ng t hs are short ; they are in the fa r-u l t raviole tpart of the electromagnetic spectrum (see Pamphlets I I and I I I ) .Absorption by Oxygen and Nitrogenat 222 Kilometers AltitudeT. M. Donahue and his team plann ed the MA-059 Exp er imen t to measure theabsorption of 1304-angstrom l igh t by oxygen a toms and 1200-angstrom l ightby nitrogen atoms between th e Apollo and the Soyuz spacecraf t . T he basicidea was to shine light from an oxyge n l a mp and a ni t rogen lamp toward

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3 ) e

0) or a;

15

'0Oxygen

Nitrogen

Nitrogen

Oxygenl A I

: 00

50T

11 5 120 125(1150) (1200) (1250) 130 135(1300) (1350)Wavelength, nm (A)

14 0( 1 4 0 0 ) 145 15 0(1450) (1500)

Emission-line spectrum (top) and absorption lines (bottom). Figure 4.3

Soyu z, w here a mirror wou ld ref lect the l ight back. On Apollo, the in tens i ty ofthe 13 04-angstrom l ine was measured and compared w i t h the source. Thedi f ference, after correction fo r mirror r e f lec t iv i ty , shows how much l ight w asabsorbed by oxygen atoms between A pollo and Soyu z. The same is t rue for the1200-angstrom l ine of ni trogen . The m irror on Soy uz w as a set of sevenretroreflectors ("cat's-eyes"), each 3.3 centimeters wide. (These "cat's-eyes" are bet ter than a plane mirror because they ref lect l igh t back in exactlyth e same di rec t ion f rom which it came.)

Light f rom the oxygen and nitrogen lamps was pointed at Soyuz as shownin Figure 4.4. Each lam p faced a concave m irror that ref lected a paral lel beamtoward Soyuz. Part of the ref lected beam returned between the two concavemirrors and was focused on the slit of a spectrometer at the left. All theM A - 0 5 9 equipment was mounted on the s ide of the Docking Module (DM)facing away from the Apollo CM, and Apollo had to be pointed so that the

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oxygen and nitrogen beams of l ight hit the retroref lector on So yuz. This w asdone by placing a bright whi te (v i s ib le ) l ight in a posit ion similar to tha t of theoxygen lamp but above the plane of Figure 4.4. The astronauts could lookout a window in the CM, past the DM, and see whether the bright whitel ight was on the Soyuz retroreflector. If i t was not, th ey corrected th e CM-D Mdirect ion w i t h th e react ion-control jets .The spectrometer (off th e left side of Fig. 4.4) w as designed to scan th efour emission l ines at 1200, 1304, 1356, an d 1493 angstroms every 12seconds. T he intensi t ies/^ were radioed to the Mission Control Center at the

From ret fo ref lectcx

To retroceflector

Figure 4.4 Schematic diagram of MA-059 lamps and mirrors.

N A S A L y n d o n B . J o h ns o n Space Ce nter (JSC) in Ho usto n, Texas. Becausethe forbidden l ines at 1356 and 1493 angstroms were not absorbed, the i rin tens i t ies checked th e ref lect ivi ty of the retroref lector, which w as norma l l yabout 0 .8 percent .

One problem was Doppler shift (see Pamphle t IV). The Apol lo and Soyuzspacecraf t were moving at an orbital speed v of 7.4 km/sec through th eoxygen and nitrogen atoms. If the l ine of sight w as a long th e velocity vector,the oxygen and nitroge n absorption w ould be shif ted by AX = \ \ - /c , w hich

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would prevent oxygen and nitrogen absorption of the emission l ines in thel ight from the oxyge n and nitrogen lamp s. Therefore, i t was plan ned to moveApollo so tha t th e beam of l ight to Soyuz w as across (perpendicular to) thevelocity vector. The easiest way to do th i s was to swing Apol lo a round th eside of S oyuz , as shown in Figures 4.5 and 4.6. This w as done three t imes:once at 150 meters separat ion, once at 500 meters separat ion, an d once at1000 meters separat ion. The idea w as tha t th e m a x i m u m absorption of the1304- an d 1200-angst rom l ines wo uld occur wh en th e Apol lo-Soyuz line ofsight was at a 90 angle to the velocity vector v. At this angle, the ref lectedbeam at 500 meters separation w as expected to be reduced by 41 percentbecause of oxygen absorption and by 20 percent because of nitrogen absorp-t ion, a ssuming th e densit ies 2 x 10 9 oxygen a toms/cm 3 and 2 x 10 7 nitrogena toms/cm 3 . If the absorptions were found to be m ore , then the densi t ieswould be higher .Another problem was the emission of the resonance l ines at 1304 and1200 angstroms by oxygen and nitrogen atoms in the beam. This emissionwould fill in the absorption l ines a l i t t lea few percent i f the Soyuz mirror(retroref lector) ref lectivity w as about 1 percent . If the Soyuz mirror were toget dirty (as it did, in fact), the direct emission-l ine inten si ty wo uld behigher, compared to the absorption l ine in the beam ref lected from a dirtymirror .

n MA-059 Oxygen andNitrogen DensityMeasurementsO n Ju ly 16, 1975, 27 hours after th e Apollo-Soyuz mission started, th eM A - 0 5 9 e q u i p m e n t on Apollo w as tested while th e outside door (off th er ight side of Fig. 4.4) w as closed. The door had small mirrors on the insidethat ref lected parts of the l a m p beams back into th e spectrometer. Scansshowed tha t emiss ion l ines were of the correct in tens i ty . After Apol lo andSoyuz undocked (separated) on Ju ly 19, Apol lo moved 18 meters ahead ofSoyuz , and the cosmonauts uncovered (by remote cont ro l ) the Soyuz re t ro-ref lectors. There were three retroref lectorsone facing up, one sideward,and one toward the backand the astronauts in Apollo could see al l threecovers open.

During the next spacecraf t nigh t , the astronau ts moved Apo llo around thesouth side of S oyuz an d spent 10 m i n u t e s in the 33 arc, 150 meters f romS o y u z , as s h o w n in Figure 4.5. The MA-059 lamps were on and the spec-t rom eter was sca nnin g, but the intensi t ies of the 1200 -, 1356-, and 1493-angstrom l ines were al l zero! The spectrom eter was w ork ing sat isfactori ly; i tdetected the 1304-angstrom airglow emission of oxygen and checked out on

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Figure 4.5 Illustration of the MA-059 150-meter data take. The symbol v represents thevelocity vector.

all four l amp emiss ion l ines af t er th e door w as closed. T he scient is ts at theMiss ion Cont ro l Center at JSC in Houston thus concluded that th e sidewardretroreflector on Soyuz was too dirty to reflect far-ul t r avio let l igh t . (Dirtcould have got ten on the re tro refl ec to r dur ing l aunch or could have com efrom a nearby oil leak.) T he scientists asked th e cosmonauts to swing Soyuz

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around to use the aft retroreflector on the second try.During the next spacecraft night, Apollo moved 500 meters north of

Soyuz along the 32 arc show n in Figure 4.6, and this t ime the spectrometerscans showed all four emission l ines during the 10 minutes that Apollomoved along that arc. However, after about 3 minutes, the intensit ies alldropped by a factor of 5, which indicated that the aft Soyuz retroreflectorhad just been dirtied. (Some oil probably leaked from Soyuz and spreadacross the face of the retroreflector .) When the MA-059 door w as closed,th e spectrometer scans were normal again.

The follow ing spacecraft nigh t, Apollo moved 800 meters above So yuzan d along the 30 arc to 1300 m eters above (Fig. 4.7). From these largerdistances, and in br ight moonl ight , th e astronauts had diff iculty keepingApollo aimed at the Soyuz retroreflector, so only a few good spectrometerscans were made. Also, the calibration check with the MA-059 door closedshowed that th e lamp beam was low by a factor of 4.

Apollo left th e vic ini ty of Soyuz an d made a slow roll with th e MA- 05 9Exper iment still on. During th is roll , the MA-059 beam was facing 90from Apollo's orbital velocity vector v, but at first th e beam was on theforward side (Fig. 4.8(a)), where the oxygen and nitrogen atoms werehi t t ing the spacecraft at 7 .4 km/sec. Later the beam was moved around toth e back side (Fig. 4.8(b)) . As expected, the emission l ines (1304 and 1200angstroms) were more intense on the front side. The gas density w as about10 t ime s high er on the "ram side" than in the "wake" of the DM.

After correcting as best they could for the ch an g in g ref lectivity and beamstrength, the MA -059 scientists collected all the m easu r em en t s of absorptionat 500 meters separation and the emission- l ine in tensi t ies tha t had beenmeasured at vary ing t imes. They concluded tha t th e densi ty at 222 ki lometersal t i tude is 1.5 x 10 8 oxygen a toms/cm 3 with an error of 20 percent and8.6 x 10 6 ni t rogen a toms/cm 3 with an error of 25 percent . These densi t iesare consistent with measurements made a t 340 k i lometers a l t i tude by theN A S A unm ann ed Atmo sphere Ex plorer sa te l l i te .

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1400 r-

1200 -

1000 -

800 -

600 -

4 on

400 -

200 -

200 -

1000 800 600 400 200Horizontal d is tance, m

200 400

Illustration of the MA-059 1000-meter data take; v is the velocity vector. Figure 4.7

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Figure 4.8 Location of MA-059 Experiment relative to the Apollo velocity vector. Thedashed lines show the direction of the beam of light.

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p Questions for Discussion(Atmosphere , Spect rum)13. By wh a t processes are gases in the lowest layer of the atmosphere

(Fig. 4.1) heated? W h y a r e troposphere temperatures near th e Equator higherthan troposphere temperatures near th e poles?14. If the gas temperature is more than 773 K (500 C) at 222 kilometers

a l t i tude , why weren' t the Apollo and Soyuz spacecraft unbearably hot?15. If a radio pulse is reflected from th e mesosphere (Fig. 4.1), wh a t is

th e echo delay?16. I f an atom h as j u s t s ix energy levels (,, E 2 , E 3 , E 4 , E. , and6) andal l jumps are allowed, how many spectrum lines can the atom absorb andreemit?17. The oxygen lam p used in the MA -059 E xperime nt produced ma ny

weaker em ission l ines at longer wav elength s (off the r ight side of Fig. 4.3).W hy wasn' t one of these l ines used to measure oxygen-atom density insteadof the 1304-angstrom line ?

18. The MA-059 Expe r iment used three different separations of Apolloan d Soyuz: 150, 500, and 1000 meters. What advantage comes with largerseparation? What disadvantages would you expect?19. How could th e dir ty-retroreflector problem be avoided?

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Appendix A

Discussion Topics (Answers to Questions)1. (Sec. 2E) The river separation x is the small side of a t r iangle 220

ki lometers long. T his triangle is s imi la r to the l ine separat ion of 0.03 mil l ime-ter on a paper 10 cent imeters away. So, Jt /220 ki lometers = 0.03 mi l l imeter /10 centimeters = sin 0.017, and A : = 66 meters. The monocula r was " x 16power," whi c h e n la rge s a ng le s 16 t i me s . S o t he 6 6 -m e t e r r i ve r se pa ra t i on j us tperceptible to the naked eye was reduced to 66/16 = 4.1 meters perceptiblew i th the monocula r .

2. (Sec. 2E) The 38 field of view of the camera corresponds to 144kilometers on the gro und . (From the center to the edge is 19, and 222 sin 19equals 72 kilometers; thus, edge-to-edge is 144 ki lometers . ) To obtain a60-percent over lap, you w ould w ant photograp hs that were 40 percent of 144or 57.5 k i lom eters apart . The t ime fo r Apol l o -S oyuz to move 57.5 ki lometersis 57.5 /7 .4 = 7.8 seconds . If the 60-m i l l imeter lens were used, th e field ofview on the ground wou l d be (100/60)144 = 240 kilometers, and the intervalw o u l d be 13 seconds .

3 . (Sec. 2E) The Hasselblad w i t h th e 250 -mi l l im eter lens g ives th e largestscale (Fig. 2.3) and therefore the best resolut ion.

4. (Sec. 2E ) "The one thi ng I noticed was that . . . l ine on the left up nearthe end . . . makes a bend to the left and fol lows a new tectonic l ine or faul twhi c h goes along pa ral lel to the Tur kish coast . In other words, the one on thelef t , numbe r 1 , goes up . . . and then mak es a left turn and para l le l s the Turkishcoas t . [N um ber] two seems to be obscured and i t just ends in a lot of jum bledcountry . . . and it seems to end r ight in t h i s j u m b l e d area. [ Num be r ] t h ree , Icould trace clear up to a river w hi ch I' l l have to see a map later. Bu t I couldtrace the f au l t s out , going ra ther eas tward . You could see them th roug h theval ley s i l t , clear up to a river w hic h must be in land in e i ther Syr ia or Turk ey.So the over al l pat tern of these is a fan; [nu mb er] three going almo st eastw ard,and [number] one bending f inal ly to the nor th, and [number] two g oing to thenor the as t . " (Verba l comments made dur ing the mission by Astronaut VanceD. Brand. ) Other reports referred to colors on the color whe e l .

5. (Sec. 2E) In Figure 2.9, there is a sharp division between re d sand andyel low sand to the left of the cente r . The grou nd-t ru th teams shou ld measurethe surface color on ei ther side of this l ine and also analyze the sand foreviden ce of i ts age. An accurate su rvey of the lat i tude and lo ng itude of a t leasttwo points a long the red-ye l low div is ion is needed to pinpoint map coordi-nates in Figure 2.9.

6 . (Sec. 2E) The distance ( r ough ly a long the Equ ator) f rom th e eastern ti p

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of South America to the "dent" in West A frica (near th e C o n g o River) whereit cam e from is about 5000 ki lometers . At 2 cm/yr , th i s cont inenta l drif t woul dtake 5 x 10 8 c e n t i me t e r s / (2 c m/y r ) = 2.5 x 10 8 years, or 250 mill ion years.

7 . (Sec. 3E ) Aerosols at high a l t i tude scatter s u n l i g h t and reduce th eamou nt reaching th e Earth's surface. Therefore, a higher aerosol count woulddecrease th e surface temperature.

8. (Sec. 3E) In addit ion to the dust -par t icle cou nts per second , you need toknow th e volume of air pumped through th e dus t -par tic le cou nte reac h second.Y ou also need th e conversion from measured outside air pressure to a l t i tude .

9. (Sec. 3E) The t ime up and back can be measured wi th an error of 30nanoseconds , so the time up to the aerosol is in error by only 15 nanoseconds.The speed of l i gh t c is 3 x 10 8 m/sec; therefore, in 15 x 10 ~ 9 seconds, l ightmoves (15 x 10 ~ 9) (3 x 10 8) = 5 x 10 ' or 0.5 meter . T he error in alt i tudethus is 50 centimeters.

10 . (Sec. 3E) Blue l igh t is refracted more than re d l i gh t , w i th other colorsin between (see P amp hlet II) . W hite -l ig ht photographs of the set t ing Sunwou l d be blue on top and red on the bot tom. A star woul d show a smal lspectrum from blue on top throu gh green, ye l low , and orange to red onth e bot tom.

11. (Sec. 3E) The Sun as seen from th e Earth or from Apollo is 0.5 indiam eter. In the triangle from lens to f i l m , the size of the Sun's image isequalto 250 mil l imeters sin 0.5 = (250 mi l l imeters )(0.0087) = 2 .2 mi l l i me t e r s indiameter .

12 . (Sec. 3E) In 93 m i n u t e s , th e Earth rotates eastward (9 3 mi nu t e s /24hours) 360 = 23. So the second sunset wou ld be 23 farther west at 95 W +23 = 118 W (wes t of Mexico).

13. (Sec. 4E) In the t roposphere, just above th e Earth's surface, the air isheated by the surface , which derives i ts heat f rom the Sun's l ight and frominfrared radiat ion that penetrates th e atmosphere. The surface passes heat tothe air directly by conduction and by radiation in long-wave inf ra red rays .Hot air rising from near the surface carries heat to higher al t i tud es byconvection. Near the Equ ator, sun l igh t strikes the E ar th ' s surface almostperpendicular to the surface, which gives the surface more heat per uni t areathan at higher la t i tudes.

14. (Sec. 4E) The high tempera ture of a very lo w dens i ty gas is mi s l e a d i ng .Because th e n u m b e r of atoms, ions, and molecules in 1 cubic meter is l ow, th e

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total energy per cubic meter is low also, and the thermal energy received byApol lo-Soyuz w as therefore very small . The spacecraft lost energy and wascooled by radia t ion. The spacecraft temperature w as control led by the balancebe tween incoming solar radiat ion and outgoing spacecraf t radiat ion. Theincoming solar radiat ion w as reduced by ref lect ive "radiat ion shields" ofmetal-covered plast ic sheets.

15. (Sec. 4E) The mesosphere is at 90 kilometers a l t i tude (Fig. 4.1), so thedistance up and back is 180 kilometers. The roun d-t r ip radio pulse t ime is180 kilometers/c = 180 kilometers/ (3 x 108 m/sec) =6 x 10 ~ 4 seconds,or an 0.0006-second echo delay.

16. (Sec. 4E) "Jumps" or "transitions" are possible between each pair ofthe six levels. An upward jump absorbs the same spectrum l ine as thedow nward ju m p emi ts be tween any two energy leve ls . Therefore , there a refive d o w n w a r d j u m p s to r four to 2> three to Ea, two to 4, and one to E5fo r a total of 15 spectrum l ines. Real a toms have many more levels andspect rum l ines than thi s s im pl i f ied exam ple .

17 . (Sec. 4E) The weaker l ines at longer wave lengths would be less effi-cien t detectors o f ox yge n atoms; that is, there w ou ld be less in tens i ty absorbedper atom in the beam between Apollo and Soyuz . B ecause th e object ive was tomeasure th e n u m b e r of oxygen a toms, th e strongest ("resonance") l ine at1304 angstroms w as best .

18 . (Sec. 4E ) W ith larger separat ion, there were more oxy gen and ni t rogena toms in the beam between Apollo and S oyuz , and the absorption could bemeasured more accura te ly . This advantage was offset by the diff iculty ofa iming the lam p beam to hit the 10-centimeter retrorefleeter on S oyuz whe n itw as 1000 meters away.

19 . (Sec. 4E) Prevent ing oil leaks and other contam ina t ion a round Soyuz isth e obvious way to keep the retroref lector c lean. A no ther solut ion wou ld be toel iminate the retroref lector and put the lamps on one spacecraf t and thespectrometer on the other.

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Quantity

Pressure

EnergyPhoton energyPowerAtomic mass

Customary UnitsQuantity

Wavelength ofl ightAccelerationof gravity

Name of unitnewton pe r squaremeterjouleelectronvoltwattatomic mass unit

Used With the SI UnitsN a m e of unit

angstrom

g

Symbol Conversion factorN /m 2 1 N /m 2 = 1.45 x lO '4 lb / in 2

J 1 J = 0.239 calorieeV 1 eV = 1.60 x 10 '19 J; 1 J = 10 7 ergW 1 W = 1 J/sec

am u 1 amu = 1.66 x 10 ~ 2 7 kg

Symbol Conversion factor

A 1 A = 0.1 nm = I Q - ' 0 m

g 1 g = 9.8 m/sec2

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Appendix C

GlossaryReferences to sect ions, Appendix A (answers to ques t ions) , and f i gu re s areincluded in the entries. Those in italic type are the most helpful .absorption line a gap or dip in a spectrum, caused by the absorption of

specific wavelengths by a gas between a l ight source and the observer.(Sees. 4A to 4C; App. A , nos. 16, 18; Figs. 4.2 , 4 .3)

aerosol very small part ic les of dus t or droplets of l iquid suspended in theEarth ' s a tmosphere . (Sees. 1, 3 , 3A to 3D; A p p . A , nos. 7 to 9 ; Figs. 3.2 ,3.3, 3.7)

altitude distance above th e Earth's surface. (Sees. 3 to 3C, 4 , 4A; A p p . A ,nos . 8, 9, 15; Figs. 3.2, 3.6,4.1)angstrom (A) a uni t of wav e length used by phy s ic i s t s for more th an 80 years ;

1 angs t rom = 10 10 meter or 0 .1 nanometer .Apollo-Soyuz a jo int U .S . -U .S .S .R . miss ion f rom July 15 to Ju ly 24, 1975.Apollo, th e three-man U.S. spacecraf t , consisted of the C o m m a n d M o d u le

(CM) connec ted to the Service Module (SM) and the Docking Module( D M ) . For 2 days , the DM was attached to S o y u z , th e t wo-ma n S ov i e tspacecraf t . The two spacecraf t were in a circular orbit incl ined 51.8 to theEqua tor , wi th a 93-m inute per iod, 222 ki lometers above the Ear th ' ssurface. See groundtrack, orbit, and Pamphlet I.

c the ve loc i ty of l ight and a l l o ther e lec tromagnet ic waves in a vacu um ,3 x 108 m/sec. (Sec. 4B; A p p . A, nos. 9, 15)

climate the weather condit ions of a region (temperature, h u m i d i t y , c l oud i -ness , r a in f a l l , s n o w f a l l , s u n s h i n e , an d w i n d s ) t h r o u g h o u t th e ye a r ,averaged over several years. (Sec. 3; App . A, no . 7 )color wheel a device fo r describing visua l color by number . (Sec . 2B )concave mirror an opt ica l com ponen t tha t ac ts l ike a lens , forming images

or g i v i n g paral lel rays f rom a point source of l ight at its focus. (Sec. 4C)continental dr if t th e very slow motion of c on t i ne n t s and the sea floors

adjacent to them (plates). (Sees. 2, 2D, 2E; App . A, no . 6)contour a l ine connec t ing po ints of equal value, such as a l t i tude on a map or

brightness on a photograph. (Sec. 3C ; Fig. 3.5(b))count one pulse of current or voltage from a detector, indicat ing the passageof a photon or part ic le through th e detector. (Sees. 3, 3A; A p p . A , nos . 7, 8;Fig. 3 .1)Docking Module (DM) a special component added to the Apollo spacecraf t

so that it could be joined wi th Soy uz. (Sec. 4C ; Fig. 4.8) S ee Pam phlet I .Doppler shift th e change of f r e que nc y / a nd wa ve l e ng t h X in the spectrum of asource approaching an observer (blue shift) or receding from him (red shif t) .

The change in wa ve l e ng t h is AX = X v /c , whe re v is the veloc i ty of approachor recession. (Sec. 4C) See Pamphle t IV .

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distant object to form an image of that o bject. (Sees. 2A, 3C; App. A ,nos. 2, 3 , 11; Figs. 2.2,2.3,3.1)

lidar a pulsed l ight detect ion and ranging ins t rument s imi la r to radar (radiodetection and ranging) . Lidar w as used to measure th e a l t i tude of aerosolsan d th e droplet characteristics. (Sees. 3B, 3D; App. A, no. 9 ; Fig. 3.3)

MA-007 th e Stratospheric Aerosol M easurem ent Ex perim ent on the Apollo-Soyuz miss ion. (Sees. 1,3, 3A, 3B, 3C, 3D; Figs. 3.2, 3.4, 3.7)MA-059 th e Ult raviole t Absorpt ion Exper im ent . (Sees. 1, 4, 4C, 4D, 4E;

A p p . A , nos. 17, 18; Figs. 4.4 to 4.8)MA-136 th e Earth Observations and Photography Exper iment . (Sees. 1, 2,

2A , 2 C , 2 D ; Figs. 2.4, 2.5)MA-148 th e Artif ic ial Solar Ecl ipse Exp er iment . (Sec.3C) See Pamphle t I I I .millibar ( i n b a r ) a uni t of pressure equal to 100 N / m 2 , used fo r me a sur i ngatmospheric pressure. (Sec. 4A ; Fig. 4.1)monocular a smal l telescope, l ike binoculars but for one eye on l y . (Sec. 2B ;

A p p . A, no. 1)orbit th e path fol lowed by a satel l ite aroun d an astronomical body, such as

the Earth or the M o o n . The orbi t number w as used on Apol lo-Soyuz toidentify th e t i m e . (Sec. 2; Fig. 3.4)

ozone (O3) a somew hat u ns table molecule formed in the Earth's a tmospherefrom atomic and m olecular oxy gen at a l t i tud es from 19 to 35 ki lom eters.(Sec. 4A ; Fig. 4.1)

photometer an i n s t r um e n t tha t uses electrical voltage to measure th e in tens i ty(br ightness) of l ight . (Sees. 3C, 3D; Fig. 3.7) There are several types;a photomult ipl ier am plif ies th e electron current . (Sec. 3 A ; Fig. 3.1)

photon a q u a n t u m of l ight the smallest separable am oun t of energy in a beamof l ight . Photon energy is proport ional to f requency and inversely pro-port ional to wa ve l e ng t h . (Sec.4B )plates the six cont inen ta l masses and the sea f loors adjacent to t he m on Earth;

subplates are segments of these plates. Plate tectonics is a s t udy of themotion of plates and subpla tes . (Sec. 2D)

Principal Investigator th e indiv idua l responsible for a space e xpe r i me n t andfo r report ing the results .

radar ( radio detect ion an d r a ng i ng ) a t ransm i t te r tha t sends a radio pulsetoward an object and measures the t ime interval un t i l the reflected (echo)pulse comes back. The t ime inte rva l g ives th e range (distance) of the object .(Sees. 3B, 4A; App. A, no. 15)

reaction-control jets smal l propuls ion u n i t s on a spacecraft used to rotate oraccelerate it in a specif ic direct ion. (Sec.4C) See Pamphle t I .reflectivity the ratio of the reflected intensity to the in tens i ty fal l ing on amirror or retroref lector. (Sees. 4C, 4D)

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refraction th e bending of electromagnetic rays such as l ight or radio waves,where th e material they are passing through changes in density, composition,or other properties. (Sees. 2D, 3C, 3D, 3E; Ap p . A, no. 10; Figs. 3.4,3.5(c), 3.6)

refractive index th e ratio of c (the velocity of l ight in a v a c u u m ) to thevelocity o f l igh t th rough a transparent substance. Each such substancelowers th e velocity of l igh t slightly and by a different a m o u n t l o w -densi ty air has a different ref rac tive index f rom high-densi ty air and fromwa ter, glass, su lfur ic acid, etc. (Sec. 3D )

resonance line a spectrum l ine resu l t ing f rom a ju m p b e tween the twolowest energy levels in an atom. A resonance l ine is strongly absorbedan d s t rongly em it ted . (Sees. 4B, 4C; Ap p . A, no. 17; Fig. 4.2)

retroreflector three mirrors perpendicular to each other ( l ike th e insidecorner of a box). These mirrors reflect any enter ing l igh t ra y back on itself.A group of seven such "corner reflectors" made up each retroreflectoron Soyuz. (Sec. 4C, 4D; Ap p . A , nos. 18, 19; Fig. 4.4)

rift a crack in the Earth 's surface, where one land mass is slid ing past anotherin pla te o r subpla te mo veme nt o f cont inenta l drif t . (Sees. 2B, 2D; F ig. 2.6)

salinity th e percentage content of salt in seawater . (Sees. 2C, 2D; Figs. 2.7,2 .1 0 )

scattered light l igh t s t r ik ing fine aerosol particles is reflected (scattered)in all direc t ions . Simi lar ly , pho tons of resonance- l ine wavelength areabsorbed by atoms and reemitted in all directions. (Sees. 3, 3B to 3D,4B ; App. A, no. 7)

spectrometer an i n s t r um e n t that spreads l ight into a spectrum and measuresth e in tens i ty at dif fe rent wav e len g th s . (Sees. 4 B , 4 C , 4 D; Ap p . A ,no. 19; Fig. 4.4)

spectrum l i gh t spread ou t in to i ts c o m p o n e n t w a v e l e n g t h s . T he f u l lelectromagnetic spectrum extends from very short gamm a rays and x-ray sth rough vis ib le l ight to infrared and long radio waves. (App. A, no. 10)Spectrum lines are peaks (emission l ines) or gaps (abso rption l ines ) ina plot of in tens i ty versus wavelength . See Pam p h le t I I .

troposphere the lowest layer of the atmosphere, just above the Earth 'ssurface, about 10 kilometers th ick . (Sees. 4A, 4E; App. A, no. 13; Fig. 4.1)velocity vector v (of Apollo-Soyuz ) the speed and direction of Ap ollo-So yuzthrough the a tmospher ic gases at 222 k i lometers a l t i tude . (Sees. 4C, 4D;Figs. 4.5, 4.6, 4.7, 4.8)wav e leng th (X) the distance from th e crest of one wav e to the crest of thenext , usua l ly measured in angst roms for l ight waves. Spectra are usua l lyplotted as in tens i ty v er su s wav e len g th . (Sees. 3C, 3E, 4A, 4B, 4E;Ap p . A, no. 17; Figs. 4.2, 4.3)

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Appendix D

Further ReadingAB C ' s of Space by Isaac Asimov, Walker and Co. (N ew York) , 1969an

illustrated glossary of spaceflight terms.Atoms and Astronomy by Paul A. Blanchard (Available from the U.S.

Government Pr in t ing Off ice , Washing ton , D.C. 20402), 1976atomicspectra explain ed in simple term s.

Continental Drif t : T he Evolution of a Concept by U r s u l a B . M a r v i n ,Smithsonian Insti tution P

Apollo-Soyuz Pamphlet No. 5 the Earth From Orbit

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Transcript of Apollo-Soyuz Pamphlet No. 5 the Earth From Orbit