Astronomical Observatories of Jai Singh II

1.Architecture in the Service of ScienceThe Astronomical Observatories of Jai Singh II Text and Photographs by Barry PerlusBetween 1724 and 1727, Jai Singh II, a re- greater scale than any that had come be-gional king under the Mogul empire, con- fore, and in certain instances, are com-structed five astronomical observatories pletely unique in design and function.in his native territory of west central In-Of the observatories originally built atdia. Passionately interested in mathemat-Delhi, Jaipur, Mathura, Ujjain, and Vara-ics and astronomy, Jai Singh adapted and nasi, all but the Mathura observatory stilladded to the designs of earlier sight-basedexist. The condition of the instrumentsobservatories to create an architecture forvaries, due to the ravages of weather andastronomical measurement that is unsur-lack of maintenance over time, but the ob-passed.servatories at Jaipur and Ujjain have haveJai Singh was influenced primarily byhad considerable restoration, and repairsthe Islamic school of astronomy, and had have been made from time to time at eachstudied the work of the great astronomersof the sites. The Jantar Mantar at New Delhi, India. The red wash on the masonry structures stands inof this tradition. Early Greek and Persian contrast to the lush green of its park-like setting in the midst of downtown New Delhi. Aobservatories contained elements that Jaipopular itinerary for foreign as well as national tourists, the site’s open space and protectedSingh incorporated into his designs, but boundaries also offer the city’s residents a quiet place for respite and contemplation.the instruments of the Jantar Mantar, asJai Singh’s observatories have come to beknown, are more complex, or at a muchAbove: Part of the Ujjain observatory.From left to right, the Samrat, Nadiva-laya, and Digamsa Yantras. Two of the twelve instruments knownPhotographs and text © 2005 Barry Perlus as the Rasivalaya Yantras, foreground, Illustrations of the principles of the instruments at the Jaipur observatory. Each of the from Virendra Sharma: Jai Singh and His Astron- Rasivalayas refers to one of the signs omy , Motilal Banarsidass, publishers - used by of the zodiac, and is designed to direct-permission. ly measure the latitude and longitudeSite plans and elevation drawings, except where The Varanasi observatory was built onPlan of the Delhi Observatory. The siteof a celestial object at the moment that otherwise noted from G. S. Kaye: The Astronom- the roof of the Man Singh palace, over-occupies an area of approximately five the sign to which it refers crosses theical Observatories of Jai Singh, published by theacres. meridian.Archaeological Survey of India. looking the Ganges. The Astronomical Observatories of Jai Singh 2. The Jaipur ObservatoryTelling Time with the LargestThe city of Jaipur is located about 220Sundial in the Worldkm south and west of New Delhi, in the The Samrat Yantra, pictured far right andState of Rajasthan. It was designed and in illustrations, below, is the largest sundialbuilt as a “new city” ca. 1727 by Jai Singh, in the world. It’s gnomon rises over 73and incorporated architectural and plan- feet above its base, and the marble facedning concepts that were advanced for quadrants, 9 feet in width, create an arctheir time. The city is also home to the that reaches 45 feet in height. According tolargest and most elaborate of the five ob- Physicist V. N. Sharma, author of Sawaiiservatories, located just across from the Jai Singh and His Astronomy:Royal Palace.The primary object of a Samrat isto indicate the apparent solar timeor local time of a place. On a clearday, as the sun journeys from east towest, the shadow of the Samrat gno-mon sweeps the quadrant scales be-low from one end to the other. At agiven moment, the time is indicatedby the shadow’s edge on a quadrant View of the Samrat Yantra at Jaipur from the North Eastscale.In order to find time with the in-a prominent star. This may be ob- used as a sighting device as Jagan- The observatory at Jaipur, above seenstrument at night, one has to knowtained from appropriate tables or natha suggests. With the quad- from atop the gnomon of the Samrat the time of the meridian transit of calculated from the knowledge thatrant edge as the vantage point, the Yantra (large sundial). The grey area in a star returns to the meridian afterobserver looks at a prominent star the site plan, below, indicates the area 23 h, 56 min, 4.09 sec, the length of through the device and moves the captured in the photograph.device back and forth along thea sidereal day. The time at nightis measured then by observing the quadrant edge SQ I (figure 1), untilhour angle of the star or its angular the star appears to graze the gno-distance from the meridian. The mon edge AC. The vantage point Vreadings then may easily be con-on the quadrant edge then indicatesverted into the mean solar time. Forthe hour angle or meridian distancemeasuring at night, a tube or slit is SV of the star, which after properconversion gives the apparent solartime.Because a Samrat, like any othersundial, measures the local timeor apparent solar time and not the“Standard Time” of a country, acorrection has to be applied to itsreadings in order to obtain the stan-dard time. The correction for IndianStandard Time is as follows: Site plan of the Jaipur observatoryIndian Standard Time = Local Figure 1 Time ± Equation of Time ± Longi-Samrat Yantra section and modelSamrat Yantra: Principle and Operation tude difference. The Astronomical Observatories of Jai Singh3. How Does It Work? cision brought forth a collection of large scale structures for the measurement of Virendra Sharma writes:time with accuracies better than ±15seconds. However, when the sun isThe first and foremost factor affect- celestial position and movement that strong, the difficulty may be elimi-Most of us are familiar with the brassing the precision of time measure- is unequalled today. Among the manynated and the procedure of mea-sundials often used as ornaments in gar-ments, and which is inherent in the startling impressions for a visitor to one suring time made objective. This isdens. These designs, known as horizontalvery design of the instrument, is the of the observatories, is the scale of the in-done by superimposing on the pen-dials, cast the sun’s shadow from a verti-width of the penumbra. For large struments. One is literally enveloped, and umbra the shadow of a thin objectcally mounted triangular plate across a Samrats, such as those at Delhi andhorizontal surface scribed with lines in- Jaipur, the penumbra could be sev-dicating the hours of the day. Due to the eral centimeters wide. The sun, be-projection of the sun’s apparent circular cause of the finite width of its disc,motion across our sky onto a flat plane, thecasts diffused shadows of objects.hour divisions are unequal, being moreAs a result, pinpointing the exact lo-closely spaced towards the noon hour. cation of the shadow-edge becomesa difficult as well as a subjectivematter. The penumbra at the GreatThe penumbra of the sun is one-halfSamrat of Jaipur, at mid-morning ondegree wide. The figure shows a highlya clear day, can be as wide as 3 cm exaggerated version of the effect.or more, making it difficult to readTime subdivisions on the quadrant scale.The smallest subdivisions, visible in thelower right corner, represent intervals oftwo seconds.Figure 2 Samrat Yantra Perspective confronted with a space that is both aes- thetic and mathematical. The time scale ofWhen the surface upon which the sun’sthe Samrat Yantra at Jaipur, for example,shadow falls is formed into a circular arc,includes subdivisions as fine as two sec-and aligned perpendicular to the earth’s onds, and as one watches, the motion ofaxis of rotation, the passage of the sun the gnomon’s shadow becomes a palpableoverhead casts a shadow which movesexperience of earth’s cosmic motion.across the surface in equal time incre-ments. This type of dial, known as “equi-noctial”, was described as early as theThe Problem of the7th century and is the design used by JaiSingh for the Samrat Yantra. Penumbra Panoramic view of the Samrat Yantrafrom ground level at the west quadrant. While the enormous size of the Samrat Accuracy and ScaleYantra generates large scales with finesuch as a needle or a string. divisions, a problem arises due to the factBy holding a one to two cm longWhen Jai Singh designed the observa- that the sun is not a single point in thetaut string parallel to the shadowtories, one of his foremost objectives was sky, but rather a disc, with finite diameter.edge, about one cm or so above theto create astronomical instruments thatExpressed in angular degrees, the sun’sinstrument’s surface, and readingwould be more accurate and permanent penumbra (the edge of the sun’s shadow)the scale where the string’s shad-than the brass instruments in use at the is one-half degree. As a consequence, theow merges with the shadow of thetime. His solution was to make them large, shadow edge is not a sharp, abrupt changegnomon edge, we could repeat ourreally large, and to make them of stone andfrom light to dark, but changes graduallyreadings with an accuracy of ±3 secDetail of Quadrant with shadowor better. The author believes thatmasonry. This simple yet remarkable de-over a distance of several centimeters.The Astronomical Observatories of Jai Singh 4. the astronomers of Jai Singh must indicates the declination of the star. the meridian at noon, its pinholeof the chamber are home to dozens of bats have used some device similar toIn this exercise, in addition to two image falling on the Shasthansawho gain entrance through ventilation that of the string for overcoming the observers, a torch bearer may also scale below enables the observer togrills in the upper section of the tower. A problem of the penumbra.be necessary to shine light on the measure the zenith distance, declil- platform about 12 feet above floor level rod on the gnomon edge for the nation, and the diameter of the sun. provides access to observe the sun’s im- principal observer near the quad- age on the quadrants. A bamboo ladder is rants below to see it clearly.The figure below shows the principle of used to reach the platform. The right ascension or RA of an its operation. object is determined by simultane- ously measuring the hour angle of Observing the center of the penumbraOther MeasurementsFigure 1In addition to marking local time, the Samrat Yantra: Principle and OperationThe principle of the Shasthansa YantraSamrat or “Great” Yantra was used to de-termine the sun’s declination and the rightthe object and the hour angle of aascension (RA) of any celestial object.reference star. From the measure- According to Virendra Sharma: ments, the difference between the right ascensions of the two is calcu- to measure the declination of the lated. By adding or subtracting this sun with a Samrat, the observer difference to the right ascension of moves a rod over the gnomon sur-the reference star, The RA of the ob-Interior of the Shasthansa Yantra face AC up or down (Figure 1) until ject is determined. the rod’s shadow falls on a quad- rant scale below. The location of the rod on the gnomon scale then givesShasthansa Yantra the declination of the sun. Decli- nation of a star or planet requiresA secondary instrument, built within theThe Shasthansa Yantra is built within the collaboration of two observers.towers that support the quadrant scales,the towers that support the great quad- One observer stays near the quad-gives extremely accurate measurements rant, as seen in this model. rants below and, sighting the star of the zenith distance, declination, and di- through the sighting device, guidesameter of the sun. Called the Shasthansa I visited the Shasthansa Yantra at Jaipur the assistant, who moves a rod upYantra, as Virendra Sharma describes, it is in December 2004 and made time lapse or down along the gnomon scale.essentially: studies of the sun’s meridian transit. The the assistant does this until the van-chamber is entered from the north wall tage point V on a quadrant edge be- . . . a 60 degre arc facing south, of either the east or west tower (there are low, the gnomon edge above wherewithin a dark chamber. The arc isDetail of the Shasthansa quadrant with duplicate instruments, one in each tower). the rod is placed, and the star—all divided into degrees and minutes.the pinhole image of the sun at noon the interior of the chamber is about 15 three—are in one line. The location High above the arc, at its center on feet wide by 30 feet long, and is open to of the rod on the gnomon scale then the south wall, is a pinhole to let a height of about 40 feet. The upper areas sunlight in. As the sun passes acrossThe Astronomical Observatories of Jai Singh5. The Jai Prakash Mirror of the HeavensThe Jai Prakash may well be Jai Singh’smost elaborate and complex instrument.It is based on concepts dating to as earlyas 300 B.C. when the Greco-Babylonianastronomer Berosus is said to have madea hemispherical sundial. Hemisphericaldials also appear in European Church ar-chitecture during the Middle Ages, and atthe observatory in Nanking, China in thelate 13th-century. The Jai Prakash, howev-er, is much more elaborate, complex, andversatile than any of its predecessors.How it WorksThe Jai Prakash is a bowl shaped instru-ment, built partly above and partly belowground level, as can be seen in the draw-ing below.The diameter at the rim of the bowl is“Unwrapped” spherical panorama from within the Jai Prakash at the Jaipur observatory. The sighting guide is visible against the sky.17.5 feet for the Jaipur instrument, and 27feet at Delhi. The interior surface is di- vided into segments, and recessed stepsCardinal points are marked on the equally-spaced circles with their between the segments provide access forrim, and cross wires are stretchedcenters on the vertical axis passing the observers. A taut crosswire, suspend-between them. A great circle drawnthrough the zenith are inscribed ed at the level of the rim, holds a metalbetween the north and the south on their surface. These circles are plate with circular opening directly overpoints and passing through theparallel to the rim and intersect the the center of the bowl. This plate serves as zenith on the instrument’s surfaceequal azimuth lines at right angles. a sighting device for night observations,represents the meridian. From the For the equatorial system, a sec- and casts an easily identifiable shadow on zenith point a number of equalond set of coordinates is inscribed. the interior surface of the bowl for solar azimuth lines are drawn up to the For these coordinates, a pooint on observation. rim or horizon. Next, a number of the meeridian, at an appropriate The surfaces of the Jai Prakash are en-distance below the south point on graved with markings corresponding tothe rim, represents the north celes- an inverted view of both the azimuth-al- tial pole. At a distance of 900 further titude, or horizon, and equatorial coordi- down, a great circle intersecting the nate systems used to describe the position meridian at right angles represents of celestial objects. See figure 4, right. the equator. On both sides of the Virendra Sharma gives a detailed de- equator, a number of diurnal circles scription of the design of the Jai Prakash:are drawn. From the pole, hour cir-In the azimuth-altitude system, cles radiate out in all directions up Plan and section of one of the Jai Prakash pairs at the Delhi observatory.the rim of each hemispherical sur-to the very rim of the instrument. Jai Prakash were built only at Jaipur andface represents the local horizon and Figure 4On a clear day, the shadow fo the Delhi. the bottom most point, the zenith.cross-wire falling on the concaveThe principle of the Jai Prakash. The Astronomical Observatories of Jai Singh6. surface below indicates the coordi- nates of the sun. These coordinates maay be read either in the horizon or in the equator system as desired. The time is read by the angular dis- tance from the meridian measured along a diurnal circle. Jai Singh’s Ingenuity:The Jai Prakash built as Complementary PairsAs described earlier, the design of the JaiPrakash was based on earlier hemispheri-cal sundials. But Jai Singh modified thisdesign to be able to make night time ob-servations. He did this by removing thearea of the concave surface between alter-nate hour circles and providing steps forthe observer to move around freely to takereadings. Working at night, the observersights the object in the sky through the cir-cular aperture plate at the intersection of Panoramic view of the interior of the Jai Prakash at Jaipur. At far left is the passageway to the companion instrument, and at far right, exitthe cross-wires. With the aid of a sighting steps to the outside. At center is the opening between hour segments of the hemispherical surface, with steps leading down to the center ofthe bowl.device attached to the concave surface theposition of the sky object is then read from above the other, they would represent a Kapala Yantrathe engraved coordinates.A second instrument was built next tosingle complete surface. In practice, when Predecessor to the Jai Prakashthe first, identical in all respects except that the shadow of the sun cast by the cross-the hour circles corresponding to the stepswire, or the coordinates of a celestial body According to maps of the Jaipur ob-in the first have a solid, engraved surface, observed at night moves past the edge of servatory dating to the early years of itsand the hour circles corresponding to theone of the engraved surfaces, the observer construction, Jai Singh built two small walks to the other instrument and contin-hemispheric dials, with a diameter of 11 ues the observation there. feet, before constructing the Jai Prakash.These instruments, named Kapala Yan-tras, were built side by side on a masonryplatform. Named Kapala A and KapalaB, the two hemispheric bowls have verydifferent functions. Kapala A has engrav-ings similar to the Jai Prakash, but lacks Plan view of the Jai Prakash at Delhi. the cutaways and size that would permitnight observations. Kapala B serves onlyengraved surface of the first are removedto transform graphically the horizon sys-to provide steps. As seen in the plan view,The Jai Prakash at Jaipur. The pattern of tem of coordinates into the equator system The Kapala A at Jaipur. The crosswire,the instruments are exact complements ofalternating areas of surface and void can and vice versa. It is the only instrument at center plate, and it’s shadow can beeach other, and if the engraved surfacesbe seen by careful comparison.Jaipur not meant for observing.clearly seen in the inset.(tinted red) of one were to be transposed The Astronomical Observatories of Jai Singh 7. Ram Yantra such that the zero mark is at the top,and the 900 mark is at the base of theis not bright enough, or if one wish-es to measure the coordinates of aor between the walls of the instru-ment. Sighting from a vacant place,central pillar. If the preference is to star or planet that does not cast a he obtains the object in the sky, theThe Ram Yantra is a cylindrical structuremeasure the zenith distance, then shadow, a different procedure istop edge of the pillar, and the van-built in pairs like the Jai Prakash. Its pri-the markings would have to be re- followed. To accomplish this, the tage point in one line. The vantagemary function is to measure the altitudeversed, i.e., the top end would now instrument is built in two comple-point, after appropriate interpola-and azimuth of celestial objects, includingdenote a 900 mark and the base of mentary units.tion gives the desired coordinates.the sun. In the Islamic and Hindu schoolsthe pillar, zero. If the vantage point lies within theof astronomy there were no insturmentsempty spaces of the walls, welllike the Ram Yantra prior to Jai Singh’sabove the floor, the observer maycreations.have to sit on a plank inserted be-Virendra Sharma gives this descriptiontween the walls. the walls haveof the principle and operation of the Ramslots built specifically for holdingYantra:such planks. Because there are noThe cylindrical structure of Ramagraduations between the emptyyantra is open at the top, and itsPlan view: Ram Yantra pair at Delhi spaces, arc lengths of wood or metalheight equals its radius. To under-to fit between the walls are neces-stand the principle, let us assumeThe two complementary units ofsary for a reading.that the instrument is built as a singleunit as illustrated in Figure 4. Thea Rama yantra may be viewed as ifcylinder, as illustrated in the figure, Figure 4obtained by dividing an intact cy-is open at the top and has a vertical lindrical structure into radial andPrinciple of the Ram Yantra, above, andpole or pillar of the same height asa plan and elevation of the Ram Yantravertical sectors. The units are suchthe surrounding walls at the cen- at Delhi, below.that if put together, they wouldter. Both the interior walls and theform a complete cylinder with anfloor of the structure are engraved open roof. The procedure for mea-with scales measuring the angles of suring the coordinates at night withazimuth and altitude. For measur- a Rama yantra is similar to the oneing the azimuth, circular scales with employed for the Jaya Prakasa. Thetheir centers at the axis of the cyl- observer works within the emptyinder are drawn on the floor of the spaces between the radial sectorsstructure and on the inner surface ofthe cylindrical walls. The scales aredivided into degrees and minutes.For measuring the altitude, a set ofequally spaced radial lines is drawnon the floor. These lines emanatefrom the central pillar and termi-nate at the base of the inner walls.Further, vertical lines are inscribed In daytime the coordinateson the cylindrical wall, which be- The gnomon (central pillar) of the Ramof the sun are determined bygin at the wall’s base and terminate Yantra at the Delhi observatory, as seenobserving the shadow of theat the top end. These lines may be through one of the arched openings inpillar’s top end on the scales, asviewed as the vertical extension ofthe outer wall. For night observationsshown in the figure. The coor- an observer can move easily betweenthe radial lines drawn on the floordinates of the moon, when it is Detail of the gnomon surface at thethe wedge shaped sectors, which areof the instrument. The radial and Delhi Ram Yantra. Weathering hasbright enough to cast a shadow,suspported at chest height by masonrythe vertical lines are inscribed with eroded and stained the engraved angu-may also be read in a similararches and posts.scales for measuring the altitude oflar markings.manner. However, if the moona celestial object, and are graduatedThe Astronomical Observatories of Jai Singh 8. Jantar Mantar on the WebVR Panoramas, 3D Models,Animations, Time Lapse Studies,Interactive Media, and OutreachOne of the objectives of the multimediaweb site www.jantarmantar.org is the cre-ation of a virtual museum to present andinterpret Jai Singh’s observatories. At thetime of writing, the web site presents aninteractive tour of the jaipur observatory, and time lapse studies illustrating theemploying navigable, immersive, VR pan- movement of the shadow of the sun on theoramas, images derived from 3D models,scales of several instruments from the ob-animations illustrating the passage of theservatories. A collaborative project withsun overhead during the course of a day,SciCentr, an outreach program of Cornell Above, an “unwrapped” rendering of a 3600 spherical panorama taken from the top of theUniversity’s Theory Center, is creating an east quadrant of the Samrat Yantra at the jaipur observatory, and above left, an undistortedinteractive 3D world in the ActiveWorlds wide-angle view from the same location. More about panoramas on the next page.Educational Development Universe. Thisproject enables science students fromparticipating middle schools and highschools to interact with a computer basedscale model of the Samrat Yantra at Jaipur,walking around it, climbing it’s stairs,and observing the methods of establish-ing local time from a simulation of themovement of the sun’s shadow across itsscales. The observatories themselves are some-times used for making observations, but One of the VR panoramas as it appears in a web browser. The user can pan andmostly serve as tourist attractions, as his-Rendering from a computer based 3D zoom through a fully spherical 3600. toric monuments and curiosities. Localmodel of the Samrat Yantraguides, many of them sanctioned by theArchaeological Survey of India, which hasauthority over the observatories, presentvisitors with a mixture of truth and fictionas they explain the history and workingsof the instruments.In contrast, Dr. Nandivada Rathnasree,director of the Nehru Planetarium, usesthe instruments of the Delhi observatoryas a real world classroom to demonstrate Students and astronomy enthusiastsprinciples of basic astronomy to students. under the guidance of Dr. NandivadaA group under her direction used the in- Rathsnasree, (in blue, lower right), useStill frame from an animation illustratingstruments at Delhi to chart the path of themakeshift crosswires to make solar ob- Screen view of the Jaipur Worldthe movement of the sun’s shadow along servations at the Delhi Jai Prakash. from Cornell University’s SciCentr planet Venus during its 2004 transit. the quadrant of the Samrat YantraThe Astronomical Observatories of Jai Singh9. More about PanoramasIn 2001 I began to use panoramic pho-tography to interpret the architecture ofthe Jantar Mantar observatories. Advanc-es in technology enabled photographersto capture multiple image panoramas andassemble the images digitally. Free view-ing software made the panoramic imagesaccessible to anyone with a computer.There are two types of panoramic ren-dering commonly in use: cylindrical andspherical.In the cylindrical panorama, a series ofoverlappping photographs is taken whilerotating the camera 3600 along the line ofthe horizon. The panorama’s vertical an-gle of view is limited by the angular cov-erage of the lens.The spherical panorama comprises a se-ries of overlapping photographs that cap-ture all areas of a scene, including directlyoverhead and directly beneath the camera.This is usually done with a digital camera, Spherical rendering from a 3600 panorama of the Jai Prakash at the Jaipur observatory.in multiple rows, with the camera point-The area along the horizontal centerline corresponds to the “equator” or maximum circum-ed along the horizon for one row, angledference of the spherical image, and thus is the least stretched. Areas at top and bottomshow the maximum stretch and distortion. At tthe very bottom, what appears to be a ribbon,upwards for a second row, and angledis actually a circular map rose with copyright information. See the photograph, lower right.downward for the third row.After the photographs are taken, they areThe top and bottom point must be stretched to span the full width of the rectangletransferred to a computer and loaded intoa program that assembles the photographsinto a composite simulating the original360 degree scene. Called “stitching’” soft-ware, these programs find the commonelements in adjacent photographs and use As seen in a browser window, thethem to seamlessly recreate the original image appears as a conventinal camera would render it.view as though it were fitted to the insideof a sphere —with the viewer at the center.The stitching software evaluates the colorsand brightnesses of adjacent photographsand creates a smooth blend between them.From this “stitched” image it is possibleto generate many kinds of images, from All points around the equator are equally distributed across the centerline of the rectangleimmersive QuickTime VR movies to pla-nar renderings (like conventional photo-graphs) to spherical renderings like theexample above.Rendering a spherical image to a 1:2 rectangleThe Astronomical Observatories of Jai Singh