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Astronomical Observatories of Jai Singh II


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Raja Jai Singh’s Observatory, Delhi. The Observatory or Jantar Mantar was constructed in1724, by Sawai Jai Singh, the Raja of Jaipur (r. 1699-1743), at the request of the Mughal Emperor Muhammad Shah …

Raja Jai Singh’s Observatory, Delhi. The Observatory or Jantar Mantar was constructed in1724, by Sawai Jai Singh, the Raja of Jaipur (r. 1699-1743), at the request of the Mughal Emperor Muhammad Shah (r. 1719-48). The Observatory in Delhi was the first to be built and was one of five-Jaipur, Ujjain, Varanasi and Mathura. A keen astronomer, Jai Singh tried to calculate planetary positions and alignments accurately.

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  • 1. Architecture in the Service of Science The Astronomical Observatories of Jai Singh II Text and Photographs by Barry Perlus Between 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 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-based exist. The condition of the instrumentsobservatories to create an architecture for varies, 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 have Jai Singh was influenced primarily by had considerable restoration, and repairsthe Islamic school of astronomy, and had have been made from time to time at eachstudied the work of the great astronomers of 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 Jai popular 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 much Above: Part of the Ujjain observatory. From left to right, the Samrat, Nadiva- laya, and Digamsa Yantras. Two of the twelve instruments known Photographs 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 longitude Site plans and elevation drawings, except where The Varanasi observatory was built on Plan of the Delhi Observatory. The site of 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 the ical Observatories of Jai Singh, published by the acres. meridian. Archaeological Survey of India. looking the Ganges. The Astronomical Observatories of Jai Singh 
  • 2. The Jaipur Observatory Telling Time with the Largest The city of Jaipur is located about 220 Sundial 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 is to indicate the apparent solar time or local time of a place. On a clear day, as the sun journeys from east to west, the shadow of the Samrat gno- mon sweeps the quadrant scales be- low from one end to the other. At a given moment, the time is indicated by the shadow’s edge on a quadrant View of the Samrat Yantra at Jaipur from the North East scale. 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 seen strument at night, one has to know tained 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 that rant edge as the vantage point, the Yantra (large sundial). The grey area in a star returns to the meridian after observer 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 the a sidereal day. The time at night is measured then by observing the quadrant edge SQ I (figure 1), until hour 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 V readings then may easily be con- on the quadrant edge then indicates verted into the mean solar time. For the hour angle or meridian distance measuring at night, a tube or slit is SV of the star, which after proper conversion gives the apparent solar time. Because a Samrat, like any other sundial, measures the local time or apparent solar time and not the “Standard Time” of a country, a correction has to be applied to its readings in order to obtain the stan- dard time. The correction for Indian Standard Time is as follows: Site plan of the Jaipur observatory Indian Standard Time = Local Figure 1 Time ± Equation of Time ± Longi- Samrat Yantra section and model Samrat Yantra: Principle and Operation tude difference. The Astronomical Observatories of Jai Singh 
  • 3. 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 ±15 seconds. However, when the sun is The first and foremost factor affect- celestial position and movement that strong, the difficulty may be elimi- Most of us are familiar with the brass ing the precision of time measure- is unequalled today. Among the many nated 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 horizontal very 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, the casts diffused shadows of objects.hour divisions are unequal, being more As a result, pinpointing the exact lo-closely spaced towards the noon hour. cation of the shadow-edge becomes a difficult as well as a subjective matter. The penumbra at the Great The penumbra of the sun is one-half Samrat of Jaipur, at mid-morning on degree wide. The figure shows a highly a clear day, can be as wide as 3 cm exaggerated version of the effect. or more, making it difficult to read Time subdivisions on the quadrant scale. The smallest subdivisions, visible in the lower right corner, represent intervals of two seconds. Figure 2 Samrat Yantra Perspective confronted with a space that is both aes- thetic and mathematical. The time scale of When the surface upon which the sun’s the 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 moves experience 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 the The Problem of the7th century and is the design used by JaiSingh for the Samrat Yantra. Penumbra Panoramic view of the Samrat Yantra from ground level at the west quadrant. While the enormous size of the Samrat Accuracy and Scale Yantra generates large scales with fine such as a needle or a string. divisions, a problem arises due to the fact By holding a one to two cm long When Jai Singh designed the observa- that the sun is not a single point in the taut 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 that Expressed in angular degrees, the sun’s instrument’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, the ow merges with the shadow of thetime. His solution was to make them large, shadow edge is not a sharp, abrupt change gnomon edge, we could repeat ourreally large, and to make them of stone and from light to dark, but changes gradually readings with an accuracy of ±3 sec Detail of Quadrant with shadow or 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 pinhole of the chamber are home to dozens of bats have used some device similar to In this exercise, in addition to two image falling on the Shasthansa who gain entrance through ventilation that of the string for overcoming the observers, a torch bearer may also scale below enables the observer to grills 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 penumbra Other Measurements Figure 1 In addition to marking local time, the Samrat Yantra: Principle and Operation The principle of the Shasthansa YantraSamrat or “Great” Yantra was used to de-termine the sun’s declination and the right the 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 gives Shasthansa Yantra the declination of the sun. Decli- nation of a star or planet requires A secondary instrument, built within the The 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, guides ameter of the sun. Called the Shasthansa I visited the Shasthansa Yantra at Jaipur the assistant, who moves a rod up Yantra, 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 where within a dark chamber. The arc is Detail 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 across The Astronomical Observatories of Jai Singh 
  • 5. The Jai Prakash Mirror of the Heavens The 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 Works The 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 steps Cardinal points are marked on the equally-spaced circles with their between the segments provide access for rim, and cross wires are stretched centers on the vertical axis passing the observers. A taut crosswire, suspend- between them. A great circle drawn through the zenith are inscribed ed at the level of the rim, holds a metal between the north and the south on their surface. These circles are plate with circular opening directly over points and passing through the parallel to the rim and intersect the the center of the bowl. This plate serves as zenith on the instrument’s surface equal 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 equal ond 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 to the 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 and face represents the local horizon and Figure 4 On a clear day, the shadow fo the Delhi. the bottom most point, the zenith. cross-wire falling on the concave The principle of the Jai Prakash. The Astronomical Observatories of Jai Singh 
  • 6. 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 Pairs As 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 of the 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 to single 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 steps wire, 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 the one 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 masonry platform. Named Kapala A and Kapala B, the two hemispheric bowls have very different 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 permit night observations. Kapala B serves onlyengraved surface of the first are removed to 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 of alternating 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 surfaces be 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 the is not bright enough, or if one wish- es to measure the coordinates of a or 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, the The Ram Yantra is a cylindrical structure measure the zenith distance, then shadow, a different procedure is top 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 altitude versed, i.e., the top end would now instrument is built in two comple- point, after appropriate interpola-and azimuth of celestial objects, including denote a 900 mark and the base of mentary units. tion gives the desired coordinates.the sun. In the Islamic and Hindu schools the pillar, zero. If the vantage point lies within theof astronomy there were no insturments empty spaces of the walls, welllike the Ram Yantra prior to Jai Singh’s above the floor, the observer maycreations. have to sit on a plank inserted be- Virendra Sharma gives this description tween the walls. the walls haveof the principle and operation of the Ram slots built specifically for holdingYantra: such planks. Because there are no The cylindrical structure of Rama graduations between the empty yantra is open at the top, and its Plan view: Ram Yantra pair at Delhi spaces, arc lengths of wood or metal height equals its radius. To under- to fit between the walls are neces- stand the principle, let us assume The two complementary units of sary for a reading. that the instrument is built as a single unit as illustrated in Figure 4. The a Rama yantra may be viewed as if cylinder, as illustrated in the figure, Figure 4 obtained by dividing an intact cy- is open at the top and has a vertical lindrical structure into radial and Principle of the Ram Yantra, above, and pole or pillar of the same height as a plan and elevation of the Ram Yantra vertical sectors. The units are such the surrounding walls at the cen- at Delhi, below. that if put together, they would ter. Both the interior walls and the form a complete cylinder with an floor of the structure are engraved open roof. The procedure for mea- with scales measuring the angles of suring the coordinates at night with azimuth and altitude. For measur- a Rama yantra is similar to the one ing the azimuth, circular scales with employed for the Jaya Prakasa. The their centers at the axis of the cyl- observer works within the empty inder are drawn on the floor of the spaces between the radial sectors structure and on the inner surface of the cylindrical walls. The scales are divided into degrees and minutes. For measuring the altitude, a set of equally spaced radial lines is drawn on the floor. These lines emanate from the central pillar and termi- nate at the base of the inner walls. Further, vertical lines are inscribed In daytime the coordinates on the cylindrical wall, which be- The gnomon (central pillar) of the Ram of the sun are determined by gin at the wall’s base and terminate Yantra at the Delhi observatory, as seen observing the shadow of the at the top end. These lines may be through one of the arched openings in pillar’s top end on the scales, as viewed as the vertical extension of the outer wall. For night observations shown in the figure. The coor- an observer can move easily between the radial lines drawn on the floor dinates of the moon, when it is Detail of the gnomon surface at the the wedge shaped sectors, which are of the instrument. The radial and Delhi Ram Yantra. Weathering has bright enough to cast a shadow, suspported at chest height by masonry the vertical lines are inscribed with eroded and stained the engraved angu- may also be read in a similar arches and posts. scales for measuring the altitude of lar markings. manner. However, if the moon a celestial object, and are graduated The Astronomical Observatories of Jai Singh 
  • 8. Jantar Mantar on the Web VR Panoramas, 3D Models, Animations, Time Lapse Studies, Interactive Media, and Outreach One of the objectives of the multimediaweb site 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 the servatories. 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 the University’s Theory Center, is creating an east quadrant of the Samrat Yantra at the jaipur observatory, and above left, an undistorted interactive 3D world in the ActiveWorlds wide-angle view from the same location. More about panoramas on the next page. Educational Development Universe. This project enables science students from participating middle schools and high schools to interact with a computer based scale 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 the movement of the sun’s shadow across its scales. 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 and mostly serve as tourist attractions, as his- Rendering from a computer based 3D zoom through a fully spherical 3600. toric monuments and curiosities. Local model of the Samrat Yantra guides, many of them sanctioned by the Archaeological Survey of India, which has authority over the observatories, present visitors with a mixture of truth and fiction as they explain the history and workings of the instruments. In contrast, Dr. Nandivada Rathnasree, director of the Nehru Planetarium, uses the instruments of the Delhi observatory as a real world classroom to demonstrate Students and astronomy enthusiasts principles of basic astronomy to students. under the guidance of Dr. Nandivada A group under her direction used the in- Rathsnasree, (in blue, lower right), use Still frame from an animation illustrating struments at Delhi to chart the path of the makeshift crosswires to make solar ob- Screen view of the Jaipur World the 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 Yantra The Astronomical Observatories of Jai Singh 
  • 9. More about Panoramas In 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 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, angled ference of the spherical image, and thus is the least stretched. Areas at top and bottom show the maximum stretch and distortion. At tthe very bottom, what appears to be a ribbon,upwards for a second row, and angled is actually a circular map rose with copyright information. See the photograph, lower right.downward for the third row. After the photographs are taken, they are The 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 rectangle The Astronomical Observatories of Jai Singh