Jantar Mantar , Jaipur, India

Jantar Mantar (“instruments and formulae”), the open-air observatory designed by Maharaja Sawai Jai Singh II, India’s last great classical astronomer, stands at the entrance to the palace in the old city of Jaipur. Built between 1728 and 1734, the group of large, modern-looking masonry structures is in fact a collection of astronomical instruments. They measure local time to an accuracy of a few seconds; the sun’s declination, azimuth, and altitude; the declination of fixed stars and planets; and they predict solar eclipses. It is the largest of the observatories established by Jai Singh II in five principal Hindustan cities; others were in Delhi, Ujjain, Mathura, and Varanasi (Benares). Only two survive: the one at Mathura was quarried for its stone and those at Ujjain and Varanasi are partly in ruins. Jantar Mantar is a remarkable architectural achievement: large buildings constructed with such exactness that they can be used as scientific instruments.
Jai Singh II, a member of the Hindu Kachhawaha dynasty, came to power at the age of thirteen. As well as being a capable general, he was so politically and intellectually gifted that the Mogul emperor Aurangzeb conferred on him the title of Sawai (literally, “a man and a quarter”). Mogul power was declining toward the end of the 1720s, but Jai Singh’s kingdom was prospering. The water supply in his fortified hillside capital, Amber, was strained by increasing population, so he moved his seat of government to the plains. In 1727 he commissioned the Bengali architect Vidyadhar Bhattacharya to design a new walled city about 125 miles (200 kilometers) southwest of Delhi and named it Jaipur. Unlike the laissez-faire contemporary north Indian cities, Jaipur’s plan was based on urban design principles found in the Hindu architectural treatise, the Shilpa Shastra. The city was divided by a right-angle grid of wide primary and secondary streets, and further by lanes and alleys, into seven rectangular zones following the caste system, related to occupations and trades. The central rectangle housed the royal complex—the palace, administrative buildings, the women’s palaces, and the Jantar Mantar.

Jai Singh II was interested in religion and the arts and sciences and his court became a magnet for savants, artists, and philosophers. He was especially interested in astronomy and acquired a multilingual library on the subject, including the works of Ptolemy and Euclid, Persian and Hindu astronomers, and modern European and Muslim sources. Beginning in 1728, he built the Jantar Mantar in Jaipur. Within high walls on three sides, the observatory covers an area of about 5 acres (2 hectares). It contains fifteen astronomical instruments built of local stone and marble. Six had solar measurement functions, eleven were for observing the night sky, and one was unfinished. These large, architecturally refined devices, capable of achieving much greater accuracy than small brass instruments, were based on Islamic astronomical theories. Most were derived from those commissioned by the fifteenth-century Byzantine ruler Ulugh Begh for the well-equipped observatory built in Samarkand in 1428.

The largest instrument at Jaipur is the equatorial sundial, a 90-foot-long (27.5-meter) straight ramp pointing toward the celestial pole. Graduated masonry quadrants on each side are centered on the nearest edge of the ramp, whose shadow marks local solar time to an accuracy of a few seconds. It was also used to determine the celestial longitude of the sun and to establish the exact time of the equinoxes. The design of another instrument, the Jai armillary sphere, has been attributed to Jai Singh II himself. It comprises two marble hemispherical bowls, each about 13 feet (4 meters) in diameter, set into the ground; their surfaces are inscribed with coordinate lines of celestial latitude and longitude. A small ring was suspended on wires over the exact center of each, and during the day its shadow marked the exact position of the sun. At night an observer could enter a room under the bowls to take sightings on the stars. The two bowls are complementary, and alternating their use within a two-hour changeover allowed continuous observation. There are also several sundials: a vertical one, hemispherical ones, and a smaller equatorial one that can measure time to about 20 seconds’ precision. Twelve smaller zodiacal instruments—one for each sign—and similar in design to the equatorial sundial, were used for observing the latitudes and longitudes of the sun and the planets. There are also two sets of tall rectangular columns arranged in circles and calibrated to allow reading of the altitude and azimuth of celestial bodies.

Finally, the astrolabe, a star chart engraved in a metal disc, is about 6.5 feet (2 meters) in diameter—six or seven times the usual size of contemporary examples—and made of a seven-metal alloy that Jai Singh had developed to minimize variations caused by temperature changes. Adjustable rulers allow the calculation of rising and setting points of the stars and planets for the accurate casting of horoscopes. That esoteric function underlines a fact that may become obscured as we marvel at the mathematical sophistication of the Jantar Mantar. It is simply this: that despite Jai Singh II’s erudition and urbane universalism, his great observatory and the others like it sprang in part from a religious and not a purely scientific source. In excellent repair after being reconstructed by Chandra Dhar Sharma Guleri in 1901, the Jantar Mantar at Jaipur was declared a national monument in 1948.