Introduction to the ObservatoryJai Singh's astronomical observatory may look like a giant playground for grownups, but in 1734, the year of its completion, it was the last outpost of medieval science. The observatory's eighteen fixed observational instruments are sighting devices which measure the position of the sun, stars and planets. Some are built entirely of masonry, others are engraved metal rings and plates set into masonry foundations.During the day, masonry sundials cast the sun's shadow on a suitably engraved scale. A sundial has two functional parts: agnomon, which is the part that casts the shadow, and ascale, from which the measurement is read. For example, in the instruments in the photo, the gnomon is an inclined ramp, and the scale is engraved on the circular part below the ramp. The sun, to the right, casts the gnomon's shadow on the curved scale to the left.Metal instruments are used for nighttime observations. They consist of a small sighting tube attached to a circular ring or plate which can pivot in various directions. They are operated by aiming the sighting tube directly at a planet or star, and then reading off its position from scales on the body of the instrument.Some instruments could be used for both daytime and nighttime observations. More information about this and other aspects of the observatory can be found in theAdditional Resourcesbelow.For all this to work, the position and orientation of the instruments and the calibration of their scales had to be minutely exact. The devices were built large, because the larger the scale, the more accurate the measurement. Once built and calibrated, they were fixed in place, could not be moved, and contained no moving parts (except of course for the pivots of the sighting instruments) or lenses. This restricted the kinds of observations that could be carried out, to those involving the positions and motions of the heavenly bodies which are visible to the naked eye.Such observations are no different in principle from those carried out in ancient Babylon, although they are considerably more accurate, and some of Jai Singh's instruments are original in design. Basically, however, this is how astronomy was done in early Mesopotamia, Egypt, Greece, China, and everywhere in the world, from the dawn of civilization down to the end of the Middle Ages.The projects carried out here included calculating the lunar calendar, predicting the start of the monsoon season, and creating astronomical tables. However, the observatory's main purpose seems to have been casting horoscopes, which requires a precise knowledge of the positions of the sun, moon, planets, and stars at the moment of birth.Because of the size and careful construction of these instruments, their accuracy was impressive by any standard. However, devices of this sort are expensive to construct. Once built, they can not be corrected or improved, and the kinds of observations they can make are limited, in the ways previously mentioned. Because of this, the instruments preserved here were conceptually obsolete even before their construction. They were soon overtaken in both usefulness and accuracy by the smaller machined brass instruments and telescopes of the modern era. Their lasting value is the tangible record they carry, a summing-up in mortar and stone of 2,500 years of premodern astronomy.

Jai SinghSawai Jai Singh, the first Maharaja of Jaipur, succeeded to the throne ofAmberin 1700 at the age of thirteen. Abandoning that capital, he founded the city of Jaipur in 1727. A soldier, ruler, and scholar with a lifelong interest in mathematics and astronomy, Jai Singh built observatories in Delhi, Jaipur, Ujjain, Mathura and Benares. Jai Singh was conversant with contemporary European astronomy through his contacts with the Portugese Viceroy in Goa. He supplied corrections to the astronomical tables of de la Hire, and published his own tables in 1723. The good state of preservation of the Jaipur observatory is due first of all to Chandra Dhar Sharma Guleri, who restored it in 1901. It has been well maintained from then to the present day.

Jantar MantarJantarmeans "instrument."Mantar(the same word as "mantra") is usually translated "formula," but here it means "calculation." So, "Jantar Mantar" means something like "instrument for calculation."

Additional ResourcesBasic Celestial Phenomena, by Kerry Magruder and Mike Keas. A good introduction to basic observational astronomy including the ecliptic, the celestial equator, and the zodiac.Jantar Mantar(1996), by Dr. Bonnie G. MacDougall at Cornell U. The Web version of an academic paper that places the observatory in its cultural context.Astronomical Instruments, from the Jiva Institute, discusses ten of the instruments and their mode of operation.Astronomical Observatory of Jaipur, by Daulat Singh Rajawat. Delta Publications, Jaipur, India. This book is sold near the observatory and elsewhere in Jaipur. It provides a useful and engaging description of the theory and practice of the observatory from a Vedic point of view.

Transcript 1. JANTAR MANTARJANTAR MANTARStone Astronomical ObservatoryStone Astronomical Observatory 2.Ancient India made some bigAncient India made some bigadvances in science becauseadvances in science becauseit was in constant contact withit was in constant contact withother countries. After theother countries. After theconquest of the Indus basin byconquest of the Indus basin byDarius around 520 B.C. IndiaDarius around 520 B.C. Indiawas thrown wide open towas thrown wide open toBabylonian influences.Babylonian influences.Through the Persians, IndiaThrough the Persians, Indiaalso came into contact withalso came into contact withGreece. All these contactsGreece. All these contactsgreatly helped India ingreatly helped India inenriching her sciences,enriching her sciences,particularly astronomy.particularly astronomy.Darius 3.There is ample evidence to show thatThere is ample evidence to show thatAryabhata (499 A.D.) and Varahamihira (6thAryabhata (499 A.D.) and Varahamihira (6thcentury A.D.) were well-acquainted withcentury A.D.) were well-acquainted withGreek astronomy.Greek astronomy.The most celebrated astronomers afterThe most celebrated astronomers afterVarahamihira were Brahmagupta (b.598Varahamihira were Brahmagupta (b.598A.D.), Lalla (8th cent.), Manjula or MunjalaA.D.), Lalla (8th cent.), Manjula or Munjala(10th cent.), Shripati (c.1039 A.D.) and(10th cent.), Shripati (c.1039 A.D.) andBhaskaracharya (b.1114 A.D.).Bhaskaracharya (b.1114 A.D.).In the post-Bhaskara period not muchIn the post-Bhaskara period not muchoriginal work in astronomy and mathematicsoriginal work in astronomy and mathematicswas done in India till modern times.was done in India till modern times.AryabhataAryabhataVarahamihiraVarahamihiraBhaskaracharyaBhaskaracharya 4. Nasir al-din at-Tusi (1201-1274 A.D.).Nasir al-din at-Tusi (1201-1274 A.D.).The last one was in- charge of theThe last one was in- charge of theobservatory at Maragha in Iran.observatory at Maragha in Iran.In 1420 A.D., Ulugh Begh, grandson ofIn 1420 A.D., Ulugh Begh, grandson ofTimur, built an observatory at Samarkand.Timur, built an observatory at Samarkand.Using very big but high-precisionUsing very big but high-precisioninstruments he prepared a Star catalogueinstruments he prepared a Star cataloguewhich was much better than that ofwhich was much better than that ofPtolemy.Ptolemy.SamarkandMaragha Omar Khayyam (1048-1124 A.D.)Omar Khayyam (1048-1124 A.D.) Al-Biruni (973-1848 A.D.)Al-Biruni (973-1848 A.D.) Al-Sufi ( 10th cent.)Al-Sufi ( 10th cent.) Tabit ibn Qurra (836-901 A.D.)Tabit ibn Qurra (836-901 A.D.) Al-Battani (850-929 A.D.)Al-Battani (850-929 A.D.) Al-Khwarismi (780-850 A.D.)Al-Khwarismi (780-850 A.D.)The Islamic world produced greatThe Islamic world produced greatmathematician-astronomers:mathematician-astronomers: 5. Later on he was appointed by MohammadLater on he was appointed by MohammadShah governor of the province of Agra andShah governor of the province of Agra andthen also of Malwa. From an early age Jaithen also of Malwa. From an early age JaiSingh was very much interested inSingh was very much interested inastronomical observations and hadastronomical observations and hadacquired thorough knowledge of itsacquired thorough knowledge of itsprinciples and rules.principles and rules. He was born in the ruling family of AmberHe was born in the ruling family of Amberin Rajasthan in 1686 A.D., one year afterin Rajasthan in 1686 A.D., one year afterNewton published his book Principia. HeNewton published his book Principia. Hesucceeded to the Amber throne at the agesucceeded to the Amber throne at the ageof thirteen.of thirteen. After a long time Sawai Jai Singh II was theAfter a long time Sawai Jai Singh II was theman from India who showed the greatestman from India who showed the greatestinterest in Arabic/Persian astronomy.interest in Arabic/Persian astronomy. 6. For observing the heavens Jai Singh builtFor observing the heavens Jai Singh builtobserv Jai Singh felt a great urge in reviving theJai Singh felt a great urge in reviving thestudy of astronomy in India. With the aim ofstudy of astronomy in India. With the aim ofpreparingpreparing new tables, Jai Singh at firstnew tables, Jai Singh at firststarted with the traditional brassstarted with the traditional brassinstruments. Realising their inadequacy, heinstruments. Realising their inadequacy, hediscarded them in favour of stone anddiscarded them in favour of stone andmasonry instruments of huge size.masonry instruments of huge size.atories at five places :observatories at five places : Delhi,Delhi,Jaipur, Mathura, Ujjain andJaipur, Mathura, Ujjain andVaranasi.Varanasi. The first one was built in DelhiThe first one was built in Delhiin year around 1724. These observatories,in year around 1724. These observatories,which in course of time came to be calledwhich in course of time came to be calledJantar Mantar, housed a wide variety ofJantar Mantar, housed a wide variety ofmasonry and metal instruments.masonry and metal instruments. 7. Jai Singhs court astronomer Pt.Jagannatha, who hadJai Singhs court astronomer Pt.Jagannatha, who hadmastered in Arabic and Persian, translated from Arabicmastered in Arabic and Persian, translated from Arabicinto Sanskrit works titled Rekhaganita and Siddhanta-into Sanskrit works titled Rekhaganita and Siddhanta-Samrata. The translation of the former was completed inSamrata. The translation of the former was completed in1718 A.D. and of the latter in 1731 A.D.1718 A.D. and of the latter in 1731 A.D. Jai Singh, making use of the masonry and metalJai Singh, making use of the masonry and metalinstruments of his observatories, prepared theinstruments of his observatories, prepared theastronomical treatise Zij-I -Muhammad Shah andastronomical treatise Zij-I -Muhammad Shah anddedicated it to the reigning monarch Muhammad Shah.dedicated it to the reigning monarch Muhammad Shah.The work was completed around 1727-28 A.D.The work was completed around 1727-28 A.D. 8. Jai Singh want to determine newJai Singh want to determine newplanetary constants but his primaryplanetary constants but his primaryinterests in astronomy centered on theinterests in astronomy centered on themoon. He was more interested inmoon. He was more interested inobserving and mathematically predictingobserving and mathematically predictingthe position of this heavenly body. He wasthe position of this heavenly body. He wasalso interested in the prediction of Solaralso interested in the prediction of Solareclipses and in calculation of theeclipses and in calculation of theoccultation of stars and planets by theoccultation of stars and planets by themoon.moon. Jai Singh had established contacts withJai Singh had established contacts withJesuit missionaries in India and had alsoJesuit missionaries in India and had alsoknown the telescope. But he did not makeknown the telescope. But he did not makeuse of the Copernican revolution ushereduse of the Copernican revolution usheredin Europe. He remained a firm follower ofin Europe. He remained a firm follower ofthe geocentric system of Indian traditionthe geocentric system of Indian traditionand of Ptolemy. It seems that Jai Singhand of Ptolemy. It seems that Jai Singhhad no knowledge of the works of Keplerhad no knowledge of the works of Kepler(1571-1630) or Newton (1642-1727).(1571-1630) or Newton (1642-1727). 9. High precision Masonary InstrumentsHigh precision Masonary Instruments Medium precision Masonary InstrumentsMedium precision Masonary Instruments Low precision Masonary InstrumentsLow precision Masonary InstrumentsJai Singh constructed 15 different types ofinstruments of masonry for his observatories. Outof these fifteen he himself invented seveninstruments. According to the precession of theinstruments it can be divide in followingcategories: 10.Jai Singh Low precision Masonary InstrumentsJai Singh Low precision Masonary InstrumentsInstrumentInstrument NumberNumber LocationLocationDhruvadarsakaDhruvadarsaka 11 JaipurJaipurNadivalayaNadivalaya 55 Jaipur,Varanasi,Ujjain,Mathura,Jaipur,Varanasi,Ujjain,Mathura,UjjainUjjainPalabhaPalabha 22 Jaipur UjjainJaipur UjjainAgraAgra 55 Jaipur,Varanasi,Ujjain,Mathura,UjjainJaipur,Varanasi,Ujjain,Mathura,UjjainSankuSanku 11 MathuraMathuraUnknown InstrumentUnknown Instrument 11 VaranasiVaranasi 11.Jai singh Medium precision Masonary InstrumentsJai singh Medium precision Masonary InstrumentsInstrumentInstrument NumberNumber LocationLocationJaiPrakasaJaiPrakasa 22 Delhi, JaipurDelhi, JaipurRama YantraRama Yantra 22 Delhi, JaipurDelhi, JaipurRasi ValayaRasi Valaya 1212 JaipurJaipurSara YantraSara Yantra 11 JaipurJaipurDigamsaDigamsa 33 Varanasi,Ujjain,JaipurVaranasi,Ujjain,JaipurKapalaKapala 22 JaipurJaipur 12.Jai singh High precision Masonary InstrumentsJai singh High precision Masonary InstrumentsInstrumentInstrument NumberNumber LocationLocationSamratSamrat66 Delhi,Jaipur(2),Ujjain,Varanasi(2)Delhi,Jaipur(2),Ujjain,Varanasi(2)SasthamsaSasthamsa55 Delhi, Jaipur(4)Delhi, Jaipur(4)Daksinottara BhittiDaksinottara Bhitti66 Jaipur,Varanasi(2),Ujjain,Mathura,Jaipur,Varanasi(2),Ujjain,Mathura,DelhiDelhi 13.Instruments added after Jai SinghInstruments added after Jai SinghInstrumentInstrument NumberNumber LocationLocationMishra YantraMishra Yantra 11 DelhiDelhiSanku YantraSanku Yantra 11 UjjainUjjainHorizontal ScaleHorizontal Scale 11 JaipurJaipur 14.Measurements Related TermsMeasurements Related TermsAzimuth:Azimuth: AzimuthAzimuth isisgenerally defined as agenerally defined as ahorizontal angle measuredhorizontal angle measuredclockwise from any fixedclockwise from any fixedreference plane.In modernreference plane.In modernastronomy it is nearlyastronomy it is nearlyalways measured clockwisealways measured clockwisefrom the north base line orfrom the north base line ormeridian. It measured inmeridian. It measured indegree and tells about thedegree and tells about thedirection of a celestial bodydirection of a celestial bodyfrom the observer.from the observer. 15.Measurements Related TermsMeasurements Related TermsAltitude: As a generalAltitude: As a generaldefinition, altitude is adefinition, altitude is adistance measurement,distance measurement,usually in the vertical orusually in the vertical or"up" direction, between a"up" direction, between areference line and a pointreference line and a pointor object. The referenceor object. The referenceline also often variesline also often variesaccording to the context.according to the context. 16. Zenith Distance:Zenith Distance: In general terms, theIn general terms, the zenithzenith is the directionis the directionpointing directly "above" a particular location . The conceptpointing directly "above" a particular location . The conceptof "above" is more specifically defined in astronomy,of "above" is more specifically defined in astronomy,geophysics as the vertical direction opposite to the force ofgeophysics as the vertical direction opposite to the force ofgravity at a given location. The opposite direction, i.e. thegravity at a given location. The opposite direction, i.e. thedirection of the gravitational force is called the nadir. Thedirection of the gravitational force is called the nadir. Theterm zenith is also used to represent the highest pointterm zenith is also used to represent the highest pointreached by a celestial body during its apparent orbit aroundreached by a celestial body during its apparent orbit arounda given point of observation.a given point of observation. MeridianMeridian : A: A meridianmeridian (or(or line of longitudeline of longitude) is an) is animaginary arc on the Earths surface from the North Pole toimaginary arc on the Earths surface from the North Pole tothe South Pole that connects all locations running along itthe South Pole that connects all locations running along itwith a given longitude. The position of a point on thewith a given longitude. The position of a point on themeridian is given by the latitude .meridian is given by the latitude .Measurements Related TermsMeasurements Related Terms 17.Hour AngleHour Angle: In astronomy, the: In astronomy, the hour anglehour angle is one of the coordinatesis one of the coordinatesused in the equatorial coordinate system for describing the position ofused in the equatorial coordinate system for describing the position ofa point on the celestial sphere. The hour angle of a point is the anglea point on the celestial sphere. The hour angle of a point is the anglebetween the half plane determined by the Earth axis and the zenithbetween the half plane determined by the Earth axis and the zenith(half of the meridian plane) and the half plane determined by the(half of the meridian plane) and the half plane determined by theEarth axis and the given point. The angle is taken with minus sign ifEarth axis and the given point. The angle is taken with minus sign ifthe point is eastward of the meridian plane and with the plus sign ifthe point is eastward of the meridian plane and with the plus sign ifthe point is westward of the meridian planethe point is westward of the meridian planeLatitudeLatitude:: LatitudeLatitude, usually denoted by the Greek letter phi (, usually denoted by the Greek letter phi () gives) givesthe location of a place on Earth (or other planetary body) north orthe location of a place on Earth (or other planetary body) north orsouth of the equator. Technically, latitude is an angular measurementsouth of the equator. Technically, latitude is an angular measurementin degrees (marked with ) ranging from 0 at the equator (lowin degrees (marked with ) ranging from 0 at the equator (lowlatitude) to 90 at the poles (90 N or +90 for the North Pole and 90latitude) to 90 at the poles (90 N or +90 for the North Pole and 90S or 90 for the South Pole).S or 90 for the South Pole). 18.EquinoxEquinox : An: An equinoxequinox occurs twice a year, when the tilt of theoccurs twice a year, when the tilt of theEarths axis is inclined neither away from nor towards the Sun,Earths axis is inclined neither away from nor towards the Sun,the Sun being vertically above a point on the Equator. The termthe Sun being vertically above a point on the Equator. The termequinoxequinox can also be used in a broader sense, meaning the datecan also be used in a broader sense, meaning the datewhen such a passage happens. The name "equinox" is derivedwhen such a passage happens. The name "equinox" is derivedfrom the Latinfrom the Latin aequusaequus (equal) and(equal) and noxnox (night), because around(night), because aroundthe equinox, the night and day are approximately equally long.the equinox, the night and day are approximately equally long.EclipticEcliptic TheThe eclipticecliptic is the apparent path that the Sun tracesis the apparent path that the Sun tracesout in the sky during the year. As it appears to move in theout in the sky during the year. As it appears to move in thesky in relation to the stars, the apparent path aligns with thesky in relation to the stars, the apparent path aligns with theplanets throughout the course of the year. More accurately, itplanets throughout the course of the year. More accurately, itis the intersection of a spherical surface, the celestial sphere,is the intersection of a spherical surface, the celestial sphere,with thewith the ecliptic planeecliptic plane.. 19. Equator :Equator : TheThe equatorequator (sometimes referre Angle of Declination:Angle of Declination: Angle at a particular point on the EarthsAngle at a particular point on the Earthssurface between the direction of the true or geographic Northsurface between the direction of the true or geographic NorthPole and the magnetic north pole. The angle of declinationPole and the magnetic north pole. The angle of declinationhas varied over time because of the slow drift in the positionhas varied over time because of the slow drift in the positionof the magnetic north pole.of the magnetic north pole.d to colloquially as(sometimes referred to colloquially as"the Line""the Line") is the intersection of the Earths surface with the) is the intersection of the Earths surface with theplane perpendicular to the Earths axis of rotation andplane perpendicular to the Earths axis of rotation andcontaining the Earths center of mass. In simpler language, itcontaining the Earths center of mass. In simpler language, itis an imaginary line on the Earths surface approximatelyis an imaginary line on the Earths surface approximatelyequidistant from the North Pole and South Pole that dividesequidistant from the North Pole and South Pole that dividesthe Earth into a Northern Hemisphere and a Southernthe Earth into a Northern Hemisphere and a SouthernHemisphere.Hemisphere. 20.JANTAR MANTAR DELHI 21.Mishra YantraMishra YantraSamarat GnomonQuadrantSecondQuadrantSamarat GnomonNiyata Cakra 22.Mishra YantraMishra YantraMishra Yantra consists of several instruments within the singleMishra Yantra consists of several instruments within the singlestructure. The instruments included in the structure are asstructure. The instruments included in the structure are asfollowsfollows::1.Daksinottra Bhitti1.Daksinottra Bhitti : for measuring the zenith distance or: for measuring the zenith distance oraltitude of sun and other planets.altitude of sun and other planets.2.Karkarasi Valaya::2.Karkarasi Valaya:: Instrument is now in ruins. Application isInstrument is now in ruins. Application isnot known and according to the theory it was used to measurenot known and according to the theory it was used to measuredirectly the longitude of celestial body.directly the longitude of celestial body.3.Samarat Yantra3.Samarat Yantra : for measuring the local time.: for measuring the local time.4. Niyata Cakras:4. Niyata Cakras: for measuring the declination of an object atfor measuring the declination of an object atinterval of a few hours as the object travels from east to west ininterval of a few hours as the object travels from east to west inthe sky.the sky.5. Quadrant arc5. Quadrant arc of unknown functionof unknown function 23.Samarat YantraSamarat Yantra 24. In addition to marking local time the Samarat YantraIn addition to marking local time the Samarat Yantrawas used to determine the sun declination and thewas used to determine the sun declination and theright ascension of any celestial object.right ascension of any celestial object. By knowing the time of the meridian transit ofBy knowing the time of the meridian transit ofprominent star and observing the hour angle of theprominent star and observing the hour angle of thestar or its angular distance from meridian time atstar or its angular distance from meridian time atnight may also calculated from this instrument.night may also calculated from this instrument. The primary object of Samarat is to indicate the solarThe primary object of Samarat is to indicate the solartime or local time of a place.time or local time of a place.Samarat YantraSamarat Yantra 25.Jai Prakesh YantraJai Prakesh Yantra 26. The instrument can measure the local co-ordinates of aThe instrument can measure the local co-ordinates of acelestial object - the Altitude and Azimuth.celestial object - the Altitude and Azimuth. Cross wires are stretched in the North-South and East-WestCross wires are stretched in the North-South and East-Westdirection on the surface of the instrument bowls. Shadow of thedirection on the surface of the instrument bowls. Shadow of thecentre of this cross wire, on the surface of the bowl, shows thecentre of this cross wire, on the surface of the bowl, shows theposition of the Sun in the sky.position of the Sun in the sky. Twin hemispherical bowls of Jai Prakas yantra are each aTwin hemispherical bowls of Jai Prakas yantra are each areflection of the sky above. The bowls are marked in sectorsreflection of the sky above. The bowls are marked in sectorsand gaps. Observers move inside the gap regions and makeand gaps. Observers move inside the gap regions and makeobservations using the markings on the sectors. Theobservations using the markings on the sectors. Theinstruments are complimentary, in the sense that where there isinstruments are complimentary, in the sense that where there isa gap in one of the bowl, is a sector placed in the other bowla gap in one of the bowl, is a sector placed in the other bowland vice versa. Spliced together, they make a whole bowl thatand vice versa. Spliced together, they make a whole bowl thatis a complete reflection of the sky above.is a complete reflection of the sky above.Jai Prakash YantraJai Prakash Yantra 27.Rama YantraRama Yantra 28.Jantar MantarJantar MantarJaipurJaipur 29.Jaipur, Jantar Mantar was the second and more sophisticatedJaipur, Jantar Mantar was the second and more sophisticatedobservatory Jai singh built.The instruments were so big andobservatory Jai singh built.The instruments were so big andaccurate ,as they were built of stone,masonry and marble.accurate ,as they were built of stone,masonry and marble.There are 18 instruments in the Jaipur observatory. HeThere are 18 instruments in the Jaipur observatory. Heprocured latest astronomical books and instruments fromprocured latest astronomical books and instruments fromEurope.Some he had translated in Sanskrit.Some of theseEurope.Some he had translated in Sanskrit.Some of thesetranslated texts are on display in the City Palace Museum.translated texts are on display in the City Palace Museum. 30.Samrat YantraSamrat YantraBy far the biggest yantra in Jantar Mantar. it is a huge SunBy far the biggest yantra in Jantar Mantar. it is a huge SunDial. It is 89 feet high and 148 feet wide. It can measureDial. It is 89 feet high and 148 feet wide. It can measurelocal time correctly up to 2 seconds..local time correctly up to 2 seconds.. 31.Chakra YantraChakra Yantra 32. For measuring the declination and hour angle of an object,For measuring the declination and hour angle of an object,a sighting tube is mounted at the centre of the instrument.a sighting tube is mounted at the centre of the instrument.The tube with a pointer attached to it, rotates about aThe tube with a pointer attached to it, rotates about aperpendicular axis passing through the centre of cakraperpendicular axis passing through the centre of cakraring. The observer rotating the cakra about its polar axisring. The observer rotating the cakra about its polar axisand the tube about the centre obtains the object in sightand the tube about the centre obtains the object in sightand the hour angle off the plate at the post.and the hour angle off the plate at the post. The Jaipur observatory has two unit of Cakra Yantra.The Jaipur observatory has two unit of Cakra Yantra.Instrument is made of heavy molded brass and pivoted toInstrument is made of heavy molded brass and pivoted torotate freely about a diameter parallel to the earth axis.rotate freely about a diameter parallel to the earth axis.Objective of the instrument is to measure the declinationObjective of the instrument is to measure the declinationand hour angle of celestial body.and hour angle of celestial body. 33.Rashivalaya YantraRashivalaya Yantra 34.There are 12 signs of the zodiac, so there are 12There are 12 signs of the zodiac, so there are 12Rasivalayas representing each sign.Rasivalayas representing each sign.At that moment its gnomon point towards the pole ofAt that moment its gnomon point towards the pole ofecliptic and its guardant become parallel to the ecliptic.ecliptic and its guardant become parallel to the ecliptic.Rasivalaya were also invented by Jai Singh. A particularRasivalaya were also invented by Jai Singh. A particularRasivalaya instrument become operative when first pointRasivalaya instrument become operative when first pointof sign of the zodiac it represents approaches theof sign of the zodiac it represents approaches themeridian.meridian.The Rasivalaya are a set of 12 instruments based on theThe Rasivalaya are a set of 12 instruments based on theprinciple of samarat yantra are designed for directlyprinciple of samarat yantra are designed for directlymeasuring the latitude and longitude of a celestial object.measuring the latitude and longitude of a celestial object. 35.Narivalaya YantraNarivalaya Yantra 36. On the vernal equinox and the autumnal equinoxOn the vernal equinox and the autumnal equinoxthe rays of the sun fall parallel to two opposingthe rays of the sun fall parallel to two opposingfaces This is an effective tool for demonstrating theThis is an effective tool for demonstrating thepassage of sun across the celestial equator.passage of sun across the celestial equator. Jai Singh built Nadivalays at each hisJai Singh built Nadivalays at each hisobservatory site except Delhi.observatory site except Delhi. After the sun has crossed the equator around 21After the sun has crossed the equator around 21March its illuminate the northern face for sixthMarch its illuminate the northern face for sixthmonths. After 21 September it is the southernmonths. After 21 September it is the southernface that receives the rays of the sun for the nextface that receives the rays of the sun for the nextsix months.six months.of plates and illuminate them both. Otherfaces of plates and illuminate them both. Othertime only one or other face remains in the sun.time only one or other face remains in the sun. 37. The main function of theThe main function of theinstrument is to measure time.instrument is to measure time. This is the largest instrumentThis is the largest instrumentin the world for its kind.in the world for its kind.Instrument is built for theInstrument is built for thelatitude of Jaipur as there arelatitude of Jaipur as there are27 degree making between the27 degree making between thezenith and the pole.zenith and the pole. Orientation of the pillars isOrientation of the pillars issuch that the line joining themsuch that the line joining themmakes an angle of about 23makes an angle of about 23degree with the plane ofdegree with the plane ofmeridian.meridian. Great astrolabe is suspendedGreat astrolabe is suspendedfrom massive wooden beamfrom massive wooden beamsupported by tall pillars.supported by tall pillars.Yantra RajYantra Raj 38.Krantiwrita YantraKrantiwrita YantraThis is the unfinished structure and has twoThis is the unfinished structure and has twocircular plates. Both the plates have a scalecircular plates. Both the plates have a scalewhich is divide in degrees.which is divide in degrees. 39.Unnatasha YantraUnnatasha Yantra 40.The rim of the brass circle has graduations marked in such away that smallest division is a tenth of a degree. The largerdivisions of 1 degree and of 6 degrees are also marked on thecircle. After sighting the celestial object, its Altitude can be readfrom the position of the pointer.The large graduated brass circle hung from the supportingbeam, is the measuring instrument of the Unnatamsa. The brasscircle is pivoted to rotate freely around a vertical axis. The ring hastwo cross beams in the vertical and horizontal directions. Asighting tube is pivoted at the centre of the circle, which can bemoved in the vertical direction, to align towards any celestialobject.Unnatamsa can measure the Altitude of a celestial object. 41.Dakshinodak Bhitti YantraDakshinodak Bhitti Yantra 42.Daksinottara BittiDaksinottara BittiDaksinottara Bitti yantra consists of aDaksinottara Bitti yantra consists of agraduated quadrant or a semicircle inscribedgraduated quadrant or a semicircle inscribedon a north-south wall. At the centre of the areon a north-south wall. At the centre of the areis a horizontal rod. The instrument is used foris a horizontal rod. The instrument is used formeasuring the meridian attitude or the zenithmeasuring the meridian attitude or the zenithdistance of an object such as the sun, the moondistance of an object such as the sun, the moonor a planet.or a planet. 43.Jai Prakash YantraJai Prakash Yantra 44.Kapala YantraKapala Yantra 45. By looking at the shadow of a cross wire stretchedBy looking at the shadow of a cross wire stretchedover its surface, the co-ordinates of the Sun in theover its surface, the co-ordinates of the Sun in thesky, can be determined with the western Kapalask The western Kapala unit is built for observations whileThe western Kapala unit is built for observations whilethe eastern segment is meant for theoreticalthe eastern segment is meant for theoreticalconversions of co-ordinates from one system toconversions of co-ordinates from one system toanother. The western Kapala unit is analogous to theanother. The western Kapala unit is analogous to theJaiprakas a hemispherical bowl on which everyJaiprakas a hemispherical bowl on which everypoint is a reflection of a point in the sky.point is a reflection of a point in the sky. The Kapala are built as two hemispherical units, eachThe Kapala are built as two hemispherical units, eachhemisphere being a complete reflection of the skyhemisphere being a complete reflection of the skyoverhead.overhead.y, can be determined with the western Kapala.. 46.One difference between the two instruments is that Kapalaindicates the a ppp while Jay Praksa observe the sign of meridian.Another is that Jay Praksa built in two complementary halves,These arcs indicate the local time and they measureastronomical parameter,such as co-ordinates of celestial body.Jai Praksa and the Kapala are both multipurpose instrumentsconsisting of hemispherical surface of concave shape andinscribed width of number of arcs.The yantra hare a diameter of 3.46 m each and are so namedbecause by there resemblance to the brain cover of human skill. 47.Ram YantraRam Yantra 48. The coordinates of the moon when it is bright enough toThe coordinates of the moon when it is bright enough tocast a shadow, may also be read in a similar manner.cast a shadow, may also be read in a similar manner. In day time the coordinates of a sun are determined byIn day time the coordinates of a sun are determined byobserving the shadow of the pillar top end on the scales.observing the shadow of the pillar top end on the scales. For measuring the azimuth, circular scales with theirFor measuring the azimuth, circular scales with theircentre at the axis of cylindrical walls. The scales arecentre at the axis of cylindrical walls. The scales aredivided into degree and minutes.divided into degree and minutes. Cylindrical structure of Rama Yantra is open at the topCylindrical structure of Rama Yantra is open at the topand its height equals its radius.and its height equals its radius. This yantra is used to measure the azimuth and altitudeThis yantra is used to measure the azimuth and altitudeof a celestial object, for example sun.of a celestial object, for example sun. The Rama yantra, probably named after Rama SinghThe Rama yantra, probably named after Rama SinghThe grandfather of Jai Singh.The grandfather of Jai Singh. 49.JANTAR MANTAR UJJAINJANTAR MANTAR UJJAIN 50.Daksinottara BittiDaksinottara Bitti 51.Daksinottara BittiDaksinottara BittiDaksinottara Bitti yantra consists of aDaksinottara Bitti yantra consists of agraduated quadrant or a semicircle inscribedgraduated quadrant or a semicircle inscribedon a north-south wall. At the centre of the areon a north-south wall. At the centre of the areis a horizontal rod. The instrument is used foris a horizontal rod. The instrument is used formeasuring the meridian attitude or the zenithmeasuring the meridian attitude or the zenithdistance of an object such as the sun, the moondistance of an object such as the sun, the moonor a planet.or a planet. 52.Samarat YantraSamarat Yantra 53.SANKUDIGAMASA 54. Cross wires are stretched between the coordinal points markedCross wires are stretched between the coordinal points markedover the outer wall. The observer uses one or more stringsover the outer wall. The observer uses one or more stringswith one end tied to a knob on the pillar and other end to stonewith one end tied to a knob on the pillar and other end to stonepebbles suspended over the walls, with these strings thepebbles suspended over the walls, with these strings theobserver defines a vertical plane contain the cross wire and theobserver defines a vertical plane contain the cross wire and theobject in the sky. The angular distance of the vertical planeobject in the sky. The angular distance of the vertical planefrom the north point, read on the scales indicate the azimuth offrom the north point, read on the scales indicate the azimuth ofbody.body. Its centre pillar as well as its wall are engraved in degrees andIts centre pillar as well as its wall are engraved in degrees andnumbers at their top level.numbers at their top level. This consists of two cylindrical wall surrounding a centreThis consists of two cylindrical wall surrounding a centrepillar measure the angle of azimuth of a celestial body.pillar measure the angle of azimuth of a celestial body.Digmasa YantraDigmasa Yantra 55.Jantar Mantar at VaranasiJantar Mantar at Varanasi 56.Some Glimpses of Jantar Mantar Varanasi 57.Some Glimpses of Jantar Mantar Varanasi 58. Unidentified structureUnidentified structure Daksinottara BhittiDaksinottara Bhitti Cakra YantraCakra Yantra NadivalayaNadivalaya DigamsaDigamsa Samarat YantraSamarat YantraJantar Mantar at VaranasiJantar Mantar at VaranasiObservatory at Vanarasi has following Instruments:Observatory at Vanarasi has following Instruments: 59.SMRAT YANTRA -------->1. Duration:dt2. Value of the velocity of light they use:c3. Duration of the flash4. Energy of the flash5. Instruments used to measure durations6. Energy collected back7. WavelengthLof the Laser ray8. Structure of the reflector on the MoonOtherwise, you can use the following results (coming from F. Mignard atCERGA):1. Duration:dt: it depends on the Earth-Moon distance when the measurement is performed.Averagedt= 2.55 seconds2. c= 299 792 458 m/s3. Duration of the impulse: 130 ps4. Impulse energy: 0.25 J5. Time measurements: Detection-emission by InAsGa diod Return detection by avalanche Si diod Duration by Dassault electronic and Cesium Clock6. Returned energy: 7 * 10-20J i.e. 1 photon for 50 shootings7. L: 532 nm8. Receptor on the Moon: retroreflectors net on a cube corner, with a 5x5 cm entrance pupil on aone square meter board.Using real values:Compute the Earth-Moon distance with these values.How accurate is the measurement? Is it the distance between Earth and Moon, or between the theCERGAlaboratory telescope and the reflector on the Moon?3. The reason for using a LaserCalculate:What would be the energy received by the reflector on the Moon (surface:s), at the distanceD, if all the energy coming from the source was sent out in all directions?If we assume that the reflector is a source sending the light in half a sphere, compute what would then be the energy received on Earth by the receiver (surface:s').Suggestion:At theCERGAsite, look for the "aperture" of the light beam sent to the Moon, and the aperture of the reflected beam.Otherwise, use the following data:Aperture of the emitted beam out of the atmosphere: 5 seconds of arc, i.e. 10 km on the Moon.Aperture of the returned beam: 3 seconds of arc i.e. 6 km on the Earth.Make the previous calculations with this values.If you can get a plan of the reflector, see the trajectory of the light rays. Show it was conceived to send the reflected light back in the same direction as the incident light whatever it may be.Try to answer this:Why is a Laser used instead of ordinary light?4. ConclusionsSuggestion:Ask astronomers what use are these measurements and which new knowledge they have brought.

Author:Frederic DAHRINGER, CLEA.

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Chapter 2Lasers in Science and Industry

Photo by: photlookToday scientists, lab technicians, engineers, and industrial technicians regularly utilize lasers to perform a wide range of important tasks. They measure distances, both short and long, with lasers, giving astronomers, geographers, and surveyors much more accurate figures than were available before the invention of these devices. They also use lasers to drill, weld, cut, and mark all sorts of materials; to study microscopic objects, including molecules; and even to fight crime.Astronomy, Geography, and SurveyingOne of the most important scientific uses for lasers is that of an advanced measuring tool. The potential of these devices to give precise figures for very long distances was shown in 1969 when theApollo 11astronauts became the first men ever to walk on the moon. Before blasting off on their return flight they left behind a bizarre-looking mirror. A short time later scientists on Earth claimed that the strange mirror had revealed to them the distance from Earth to the moon, a figure that was accurate to within the length of a person's finger. This moon mirror was neither mysterious nor magical, though it would have seemed so to many people only a few years before. In reality, National Aeronautics and Space Administration (NASA) scientists had instructed the astronauts on exactly how to position the mirror as part of a plan to measure the Earth-to-moon distance with alaserbeam.Before lasers existed, scientists already had a fairly good idea of how far away the moon is. But "fairly good" is not good enough in science. Scientists want their measurements to be as exact as possible, and bouncing a laser beam off the mirror promised to give

U.S. astronaut Buzz Aldrin stands on the moon's surface. There, the astronauts placed a special mirror designed to reflect back a laser beam sent from Earth.them more accurate figures than ever before. The experiment used the simple formula

The scientists already knew the speed of light, so they knew what the rate of travel was. When the beam bounced off the mirror, it returned to Earth and registered on special sensors. These recorded how long the beam took to make a round trip, and scientists then knew the time factor in the equation. After some simple multiplication, they finally had the most accurate measurement of the Earth-to-moon distance possible. Knowing this has enabled them to learn much about the relationship between Earth and its natural satellite. For instance, researchers have repeated this laser-mirror experiment every year since 1969. They have found that the moon is moving away from Earth at a rate of about one and a half inches (four centimeters) a year.Measuring distance by means of lasers and mirrors works just as well on Earth as it does in space. Every day, surveyors use lasers to measure the distances between houses, roads, and mountains. A device called a range finder utilizes the same principle as the moon mirror; a surveyor aims a laser beam at a reflective target and the beam bounces back to the range finder, which records the time of the round-trip and uses this figure to calculate the exact distance to the target. This method is more accurate and also much faster than oldersurveyingmethods, which required many calculations with poles and telescopes that had to be lined up with one another. Erecting skyscrapers, excavating tunnels and canals, laying pipelines, drilling wells, leveling farmland (making it flatter and easier to exploit) are only a few of the many other projects made easier by precise laser measurements. Such measurements also have led to more exact and reliable maps; using lasers,mapmakershave now charted almost every square mile of Earth's surface.Laser Toolbox TechnologySuch precise measurement is just one of several jobs that, before the advent of lasers, were associated with what engineers and others call "toolbox" technology. Every toolbox has itsyardstick, ruler, or tape measure. It also has a drill to bore holes and a hacksaw to cut metal. Larger toolboxes include welding equipment to join pieces of metal together. Just as lasers have come to replace the yardstick in measuring, they also have replaced the drill, the saw, and the welder. The era of the toolbox laser has arrived.Measuring Distances with LasersLasers can measure enormous distances with great accuracy. A laser beam travels at a constant speed (the speed of light). The time it takes a laser beam to travel from its source, reflect off an object, and return to the source, will indicate the exact distance between the source and the object.Lasers perform some toolbox jobs better and faster because of some unusual properties of laser light itself. In the first place, laser light is extremely bright, so bright that laser operators always wear protective glasses. The light is so intense because its energy is very concentrated; there are a great number of photons in a relatively small beam.Properties of Laser LightThe photons of laser light are collimated. In other words, they all travel from the laser in the same direction. Laser light is also coherent, meaning that all the waves in a laser beam have the same wave pattern. These properties make laser light more intense than ordinary light and allow it to travel long distances. Ordinary light waves scatter in all directions from their source. Also, an ordinary beam of light is incoherent, meaning that it contains waves of many different patterns, which tend to interfere with one another.

Laser light is also highly directional, or collimated. This means that all the photons travel in the same direction. They tend to stay together rather than spread apart as the photons in ordinary light do. The farther a beam of ordinary light travels, the more it spreads out and gets dimmer. On the other hand, collimated laser light can travel a great distance without losing very much of its energy and brightness. Ordinary light could never have made it to the moon mirror and back, whereas laser light did quite easily.There is one more important quality of laser light. It is coherent, or very organized. This means that the light waves are lined up with each other and moving along in step, almost like a regiment of soldiers marching in a parade. By contrast, ordinary light is incoherent. Its waves become mixed up as they move along, like the crowd of people watching the parade. So, the laser light is special. It is concentrated, directional, and organized.These three qualities combine to make the laser an extremely powerful and useful tool in materials processing, the industrial manipulation of metals, plastics, wood, ceramics, cloth, and other materials for making a wide range of products. Breck Hitz, an expert on industrial lasers, elaborates:Lasers are used to cut, drill, weld, heat-treat, and otherwise alter both metals and nonmetals. Lasers can drill tiny holes inturbineblades more quickly and less expensively than mechanical drills. Lasers have several advantages over conventional techniques of cutting materials. For one thing, unlike saw blades or knife blades, lasers never get dull. For another, lasers make cuts with better edge quality than most mechanical cutters. The edges of metal parts cut by a laser rarely need to be filed or polished because the laser makes such a clean cut.1Drilling and Burning Holes with LightA laser beam excels as an industrial drill because it can be focused into a tiny bright point. Of course, ordinary light can be focused in a similar way. For instance, a magnifying glass held up to the sun will focus the sun's rays into a tiny, very bright point, a point that is also hot enough to burn a leaf or ignite a piece of paper.Now consider collimated laser light, which is hundreds of times more directional than ordinary light. It can be focused to produce a beam of light, much hotter than the surface of the sun, that can cut cleanly through a thick metal bar in a few millionths of a second.One of the more important uses of the laser drill in industry is in the production of copper wire. The wire is formed by forcing copper metal into a small round hole that a laser has drilled into a diamond. The hard diamond acts like a mold, and the much softer copper squeezes out the other end in the form of wire. The old method of drilling holes in industrial diamonds was very time-consuming and expensive. Since the only naturally occurring material hard enough to cut through a diamond is another diamond, workers had to use diamond drills. But diamonds are expensive. Furthermore, the drilling process took several hours, so a worker could drill only two or three holes in a workday. In contrast, a laser beam drills holes in diamonds at the speed of light. One worker using one laser can bore hundreds or even thousands of holes in a single hour. And the same method is used for drilling holes in other gems that are used as moving parts in watches.

These tiny diamond dies used in telephone lines have been drilled with laser beams. Such small holes could not be cut in diamonds without lasers.Though it might seem surprising, lasers are also effective in boring holes in very soft materials. Some of these materials are easily stretched or torn by ordinary methods. An excellent example is the common baby bottlenipple. A laser beam burns a perfectly round hole in the top of the nipple without disturbing any of the surrounding rubber. Similarly, lasers are used to drill tiny holes in the soft plastic valves of spray cans (such as those of hair spray or glass cleaner). One such laser can punch over a thousand valve holes in one minute.Welding and Cutting with LasersAnother industrial application of lasers is welding. The advantage of the laser over normal welding methods is similar to its advantage in other industrial areas. The laser is hotter, faster, more accurate, and also safer because the welder does not have to go near the hot metal.Laser welding works on both large and small scales. On the large scale, theU.S. Navyuses lasers to weld together huge metal parts in shipbuilding. Experts estimate that millions of dollars are saved in the welding process and millions more in reduced need for later repairs. Such common items as automobile spark plugs, portable batteries, and metal braces for the teeth are also routinelyweldedby laser beams.On a smaller scale, lasers weld the parts for tiny electrical circuits used in computers, calculators, and miniature television sets. In the past, welding these small parts was accomplished by solderingmelting a metallic substance called solder around them to ensure a proper electrical connection. But soldering tools cannot be made small enough to weld the very tiny electrical parts now being produced; and manipulating the smallest available soldering tools is very painstaking work, produces uneven results, and can damage the delicate parts. By contrast, such tiny welds, some of them even microscopic, are easily made by the hot, razor-thin beam of a carbon dioxide laser.In industry the opposite of welding is cutting, another essential process for making all manner of products.

A technician uses a laser to cut holes in carbon steel, one of the hardest of all artificial substances.Every good toolbox has a hacksaw and a pair ofscissors; the saw to cut metal, the scissors to cut cloth. The toolbox laser can do the jobs of both. Making saw blades themselves is an excellent example of using lasers to cut metal. The old methods of producing saw blades involved many steps, each of which required a person to handle the blades with his or her hands; not surprisingly, injuries were common. In contrast, a laser cuts the blade out of the sheet metal in only one step. Only the beam touches the metal, so as long as the operator is wearing protective glasses there is no chance for injury. In addition, reflective substances like glass can be cut by a laser if their surfaces are first coated with a dark substance. That way the laser light is absorbed rather than reflected.An example of the use of "laser scissors" is to cut patterns for clothes. A laser cloth-cutting system was designed by Hughes Aircraft, the company that employed Theodore Maiman, the inventor of the ruby laser. The system works in the following way: Pieces of cloth are laid out on a large table while the patterns are entered into a computer, which decides the best way to trace them out on the cloth. Next, the computer directs the laser beam to cut out the traced patterns very precisely. Cloth for hundreds of suits can be cut in an hour, and as an added advantage the heat of the beam keeps the edges of the cloth from fraying.Such laser scissors can be made to work on a microscopic level as well, not only in industry but also in biological research. Scientists who study and attempt to manipulate plant or animal cells can use a laser beam to make tiny alterationsin a sense performing microsurgeryon such cells. Recent experiments show that the use of lasers also can eliminate a serious obstacle to such microscopic manipulation; namely, the difficulty of holding a cell in place while working on it. To accomplish this task laser scissors are often accompanied by "laser tweezers," as explained by University of California scholar Michael Berns:That light can heat or burn, measure or calibrate makes sense. But the idea of light creating a force that can hold and move an object may seem as fanciful as a Star Trek tractor beam. Still, light has momentum [a forward-pushing force] that can be imparted to a target. The resultant [very small] forces fall far below our sensory awareness when, for example, the sun's light falls on and imperceptibly pushes against us. But these forces can be large enough to influence biological processes at the subcellular level, where the masses of the objects are [extremely tiny]. . . . When the geometry of the arrangement of light beams and target is correct, the momentum imparted to the target pulls the target in the direction of the . . . laser beam, and the beam can thus hold the target in place. By moving the beam, the laser operator can pull the target from place to place.2Fighting Crime with LasersThe toolbox laser can even be used, along with other scientific tools such as DNA testing, to fight crime. A laser beam can scan a computerized record of millions of criminals' fingerprints, for instance, and in a few seconds pick out one that matches a print found at a crime scene. Laser beams can also detect extremely minute and very old traces of perspiration and other human body secretions. In the 1990s the FBI investigated a man they believed to be a former German Nazi in World War II. He denied the charge. But then the FBI obtained apostcardwritten by the Nazi in 1942, and a laser was able to find traces of body oils on the card; the oils were identical to those of the suspect, who was found guilty and imprisoned.In another example of lasers acting as detectives, some people are recovering stolen gems thanks to a system called laser identification. An ID marking is carved into the gem by a laser that creates a thin and accurate beam. This beam, which is so tiny it can cleanly drill more than two hundred holes in the head of a pin, carves or etches microscopic numbers, words, people's names and addresses, or entire messages on any material, no matter how smooth or hard. This includes precious gems like emeralds and diamonds. The result is an ID marking so tiny that no one, including a thief, can detect it with the naked eye. Many other valuable items are now marked in this manner by laser beams.Almost every day several new uses are found for toolbox lasers. The devices are still rather expensive, so

In addition to marking guns with tiny ID numbers, lasers can be used to detect finger-prints on handguns and other weapons.they are not yet normally found in home toolboxes. But this situation will surely change. As laser research continues, ways will be found to produce these tools more simply and cheaply. In the near future a laser hanging above the basement workbench may become a common sight.Tweets by @cool_luxuryUser Contributions:

1Raj

Aug 12, 2009 @ 11:23 pmThis is very useful for School sudent,Thanks for ur thoery

2abirami

Nov 20, 2009 @ 12:00 amThis article is very nice.we use this article for our project.we also get good comment for our project.thank you very much for providing this article.

3Aaron

Jan 10, 2011 @ 9:21 pmThis was a great article for my school report on lasers, thank you very much for providing this page. I got good comments for report from my teacher and classmates.

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Lunar Laser Ranging experimentFrom Wikipedia, the free encyclopedia

The Lunar Laser Ranging Experiment from the Apollo 11 mission.The ongoingLunar Laser Ranging Experimentmeasures thedistancebetween theEarthand theMoonusinglaser ranging.Laserson Earth are aimed atretroreflectorsplanted on the Moon during theApollo program(11, 14, and 15), and the time for the reflected light to return is determined.

Apollo 15 LRRR

Apollo 15 LRRR schematicThe first successful tests were carried out in 1962 when a team from theMassachusetts Institute of Technologysucceeded in observing laser pulses reflected from moon's surface using a laser with a millisecond pulse length. Similar measurements were obtained later the same year by a Soviet team at theCrimean Astrophysical Observatoryusing aQ-switchedruby laser.[1]Greater accuracy was achieved following the installation of aretroreflectorarray on July 21, 1969, by the crew ofApollo 11, and two more retroreflector arrays left by theApollo 14andApollo 15missions have also contributed to the experiment. Successful lunar laser range measurements to the retroreflectors were first reported by the 3.1m telescope atLick Observatory,Air Force Cambridge Research LaboratoriesLunar Ranging Observatory in Arizona, thePic du Midi Observatoryin France, the TokyoAstronomical Observatory, andMcDonald Observatoryin Texas.The unmanned SovietLunokhod 1andLunokhod 2rovers carried smaller arrays. Reflected signals were initially received fromLunokhod 1, but no return signals were detected after 1971 until a team from University of California rediscovered the array in April 2010 using images fromNASA'sLunar Reconnaissance Orbiter.[2]Lunokhod 2'sarray continues to return signals to Earth.[3]The Lunokhod arrays suffer from decreased performance in direct sunlight, a factor which was considered in the reflectors placed during the Apollo missions.[4]TheApollo 15array is three times the size of the arrays left by the two earlierApollomissions. Its size made it the target of three-quarters of the sample measurements taken in the first 25 years of the experiment. Improvements in technology since then have resulted in greater use of the smaller arrays, by sites such as theCte d'Azur ObservatoryinGrasse,France; and theApache Point Observatory Lunar Laser-ranging Operation(APOLLO) at theApache Point ObservatoryinNew Mexico.Contents[hide] 1Details 2Results 3Photo gallery 4See also 5References 6External linksDetails[edit]The distance to the Moon is calculatedapproximatelyusing this equation:Distance = (Speed of light Time taken for light to reflect) / 2.In actuality, the round-trip time of about 2.5 seconds is affected by the relative motion of Earth and the Moon, Earth's rotation,lunar libration,weather,polar motion, propagation delay throughEarth's atmosphere, the motion of the observing station due tocrustal motionandtides, velocity of light in various parts of air andrelativistic effects.[5]Nonetheless, the EarthMoon distance has been measured with increasing accuracy for more than 35 years. The distance continually changes for a number of reasons, but averages about 384,467 kilometers.At the Moon's surface, the beam is about 6.5 kilometers wide[6]and scientists liken the task of aiming the beam to using a rifle to hit a movingdime3 kilometers away. The reflected light is too weak to be seen with the human eye: out of 1017photons aimed at the reflector, only one will be received back on Earth every few seconds, even under good conditions. They can be identified as originating from the laser because the laser is highlymonochromatic. This is one of the most precise distance measurements ever made, and is equivalent in accuracy to determining the distance between Los Angeles and New York to 0.25 mm.[4][7]As of 2002work is progressing on increasing the accuracy of the EarthMoon measurements to near millimeter accuracy, though the performance of the reflectors continues to degrade with age.[4]Results[edit]Lunar laser ranging measurement data is available from the Paris Observatory Lunar Analysis Center,[8]and the active stations. Some of the findings of thislong-term experimentare: The Moon is spiraling away from Earth at a rate of 3.8cm per year.[6]This rate has been described as anomalously high.[9] The Moon probably has a liquid core of about 20% of the Moon's radius.[3] The universal force ofgravityis very stable. The experiments have constrained the change inNewton'sgravitational constantGto (27)1013per year.[10] The likelihood of any "Nordtvedt effect" (a differential acceleration of the Moon and Earth towards the Sun caused by their different degrees of compactness) has been ruled out to high precision,[11][12]strongly supporting the validity of theStrong Equivalence Principle. Einstein'stheory of gravity (thegeneral theory of relativity) predicts the Moon'sorbitto within the accuracy of the laser ranging measurements.[3]Photo gallery[edit] Apollo 14 Lunar Ranging Retro Reflector (LRRR). APOLLO Collaboration photon pulse return times Laser ranging facility atWettzellfundamental station,Bavaria,Germany. Laser Ranging atGoddard Spaceflight Center.

See also[edit]Moon portal

Apache Point Observatory Lunar Laser-ranging Operation Apollo Lunar Surface Experiments Package Tom Murphy (Physicist)(principal investigator of Apollo's reflector experiment) Carroll Alley(previous principal investigator of Apollo's reflector experiment) EME (communications) Lidar Lunar distance (astronomy) Lunokhod programme Satellite laser ranging Third-party evidence for Apollo Moon landingsReferences[edit]1. Jump up^Bender, P. L.; Currie, D. G.; Dicke, R. H. et al. (October 19, 1773)."The Lunar Laser Ranging Experiment"(PDF).Science182(4109): 229238.Bibcode:1973Sci...182..229B.doi:10.1126/science.182.4109.229.PMID17749298. RetrievedApril 27,2013.2. Jump up^McDonald, Kim (April 26, 2010)."UC San Diego Physicists Locate Long Lost Soviet Reflector on Moon". UCSD. Retrieved27 April2010.3. ^Jump up to:abcJames G. Williams & Jean O. Dickey."Lunar Geophysics, Geodesy, and Dynamics"(PDF). ilrs.gsfc.nasa.gov. Retrieved2008-05-04.13th International Workshop on Laser Ranging, October 711, 2002, Washington, D. C.4. ^Jump up to:abc"Its Not Just The Astronauts That Are Getting Older". Universe Today. March 10, 2010. Retrieved24 August2012.5. Jump up^Seeber, Gunter.Satellite Geodesy 2nd Edition. de Gruyter, 2003, p. 4396. ^Jump up to:abFred Espenek (August 1994)."NASA - Accuracy of Eclipse Predictions". eclipse.gsfc.nasa.gov. Retrieved2008-05-04.7. Jump up^"Apollo 11 Experiment Still Going Strong after 35 Years". www.jpl.nasa.gov. July 20, 2004. Retrieved2008-05-04.8. Jump up^"LUNAR LASER RANGING OBSERVATIONS FROM 1969 TO MAY 2013"SYRTE Paris Observatory, retrieved 3 June 20149. Jump up^Bills, B.G. & Ray, R.D. (1999),"Lunar Orbital Evolution: A Synthesis of Recent Results",Geophysical Research Letters26(19): 30453048,Bibcode:1999GeoRL..26.3045B,doi:10.1029/1999GL00834810. Jump up^Mller, Jrgen; Liliane Biskupek (2007)."Variations of the gravitational constant from lunar laser ranging data".Classical and Quantum Gravity24(17): 4533.doi:10.1088/0264-9381/24/17/017. Retrieved7 May2014.11. Jump up^Adelberger, E.G.; Heckel, B.R.; Smith, G.; Su, Y. & Swanson, H.E. (20 September 1990), "Etvs experiments, lunar ranging and the strong equivalence principle",Nature347(6290): 261263,Bibcode:1990Natur.347..261A,doi:10.1038/347261a012. Jump up^Williams, J.G.; Newhall, X.X. & Dickey, J.O. (1996), "Relativity parameters determined from lunar laser ranging",Phys. Rev. D53: 67306739,Bibcode:1996PhRvD..53.6730W,doi:10.1103/PhysRevD.53.6730External links[edit] Apollo 15 Experiments - Laser Ranging Retroreflectorby theLunar and Planetary Institute "History of Laser Ranging and MLRS"by theUniversity of Texas at Austin, Center for Space Research "Lunar Retroreflectors"by Tom Murphy Station de Tlmtrie Laser-LuneinGrasse, France Lunar Laser Rangingfrom International Laser Ranging Service "UW researcher plans project to pin down moon's distance from Earth"by Vince Stricherz,UW Today, January 14, 2002 "What Neil & Buzz Left on the Moon"by Science@NASA, July 20, 2004 "Apollo 11 Experiment Still Returning Results"by Robin Lloyd,CNN, July 21, 1999[show] v t eThe Moon

[show] v t eApollo program hardware

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