List of Indian astronomers

City of Jaipur, State of Rajasthan, India.

Latitude 26° 55′ 29″ N, longitude 75° 49′ 28″ E. Elevation 440m above mean sea level.

The Jantar Mantar of Jaipur is an observatory built in the first half of the 18th century. Today it has 19 main astronomical instruments or groups of instruments. They were generally constructed of brick rubble and plaster, but a few were made of bronze. They were built for naked-eye observations of the celestial bodies and precision was achieved through their monumental dimensions. Generally speaking, they replicated the design of earlier instruments, but the site shows important architectural and instrumental innovations and the size of some of the instruments is among the largest in the world. There are instruments working in each of the three main classical coordinate systems: the horizon-zenith local system, the equatorial system and the ecliptic system. One instrument (Kapala Yantra) is able to work in two systems and to transform coordinates directly from one system to the other. This is one of the most complete and impressive collections in the world of pre-telescopic masonry instruments in functioning condition.

The most significant instruments (yantras) among the collection are:

• Brihat Samrat, probably the largest gnomon-sundial ever built. With a gnomon arm 22.6m high and two lateral quadrants of radius 15.15m, it measures local time to an accuracy of 2 seconds.
• Sasthamsa, which has four large meridian dials inside two high black chambers.
• Jai Prakash, a highly innovative sundial made of two hemispherical bowls that produce an inverse image of the sky and allow the observer to move freely around inside to take readings.
• Great Ram is a rare, and perhaps unique, double-cylinder instrument to record the azimuth of celestial bodies;
• Raj comprises a bronze astrolabe 2.43m in diameter, probably the largest in the world.
• Kapala is able to record the co-ordinates of celestial bodies in both the azimuth-altitude and equatorial systems, and permits a direct visual transformation of the co-ordinates of any point in the sky between the two systems;
• Rasivalaya is a unique group of 12 gnomon-dials to measure the ecliptic co-ordinates of celestial objects, each becoming operative when a different one of the 12 zodiacal constellations straddles the meridian.

The Jantar Mantar Observatory was built by Maharaja Sawai Jai Singh II, as a focal point of his new capital, Jaipur, the first and earliest geometrically planned city in India. Jai Singh II was one of several powerful princes rising to power as the influence of the Mughal Empire decreased. In his attempt to become an almost independent ruler of Rajasthan, he started to build a new capital underlining the link between scientific capacities, urban planning and social control. The construction of the observatory site started in the 1720s and was completed in 1738.

Jantar Mantar is the most complete and best-preserved great observatory site built in the Ptolemaic...