Architecture in the Service of Science the Astronomical Observatories of Jai Singh II
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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 function. in his native territory of west central In- Of the observatories originally built at dia. Passionately interested in mathemat- Delhi, Jaipur, Mathura, Ujjain, and Vara- ics and astronomy, Jai Singh adapted and nasi, all but the Mathura observatory still added to the designs of earlier sight-based exist. The condition of the instruments observatories to create an architecture for varies, due to the ravages of weather and astronomical 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 repairs the Islamic school of astronomy, and had have been made from time to time at each studied the work of the great astronomers of the sites. The Jantar Mantar at New Delhi, India. The red wash on the masonry structures stands in of this tradition. Early Greek and Persian contrast to the lush green of its park-like setting in the midst of downtown New Delhi. A observatories contained elements that Jai popular itinerary for foreign as well as national tourists, the site’s open space and protected Singh 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, as Jai Singh’s observatories have come to be known, 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 Archaeological Survey of India. looking the Ganges. acres. meridian. The Astronomical Observatories of Jai Singh The Jaipur Observatory Telling Time with the Largest The city of Jaipur is located about 220 Sundial in the World km south and west of New Delhi, in the The Samrat Yantra, pictured far right and State of Rajasthan. It was designed and in illustrations, below, is the largest sundial built as a “new city” ca. 1727 by Jai Singh, in the world. It’s gnomon rises over 73 and incorporated architectural and plan- feet above its base, and the marble faced ning concepts that were advanced for quadrants, 9 feet in width, create an arc their time. The city is also home to the that reaches 45 feet in height. According to largest and most elaborate of the five ob- Physicist V. N. Sharma, author of Sawaii servatories, 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 through the device and moves the captured in the photograph. 23 h, 56 min, 4.09 sec, the length of a sidereal day. The time at night device back and forth along the 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 Site plan of the Jaipur observatory Standard Time is as follows: 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 cision brought forth a collection of large Virendra Sharma writes: time with accuracies better than ±15 How Does It Work? scale structures for the measurement of 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 is dens. 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 object cally mounted triangular plate across a Samrats, such as those at Delhi and horizontal 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 of axis of rotation, the passage of the sun the gnomon’s shadow becomes a palpable overhead 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 the 7th century and is the design used by Jai Singh 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 shadow tories, one of his foremost objectives was sky, but rather a disc, with finite diameter. edge, about one cm or so above the to create astronomical instruments that Expressed in angular degrees, the sun’s instrument’s surface, and reading would 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 the time. His solution was to make them large, shadow edge is not a sharp, abrupt change gnomon edge, we could repeat our readings with an accuracy of ±3 sec really large, and to make them of stone and from light to dark, but changes gradually Detail of Quadrant with shadow masonry.