Raja Sawai Jai Singh II of Jaipur was a genius in his own right. He drew a blueprint of an astronomical observatory, with large masonry astronomical instruments designed to make specific calculations and measurements. Between 1727 and 1734, five royal observatories were built on the blueprint in Delhi
, Mathura, Varanasi
, and Ujjain. The observatories of Delhi and Jaipur are the ones that have been preserved well.
The Jantar Mantar at Jaipur is still in use and is known to make accurate calculations up to two decimal points. It is also the largest of all the observatories built by the Raja. The unique design of the instruments has attracted the attention of artists, architects, art historians, and media worldwide. The observatory had a religious significance too as ancient Indian astrologers or Jyotishis relied on astronomical calculations to come up with accurate predictions.
There are as many as fourteen devices at the Jantar Mantar in Jaipur that were used for definite functions such as measuring time, tracking stars and their orbits, ascertaining planetary movements, measuring celestial altitudes and predicting eclipses. The largest instrument is the Samrat Yantra, a Giant Sun Dial that used shadow to tell the local time of Jaipur. It is situated at an angle of 27 degrees, the latitude of Jaipur, and is 27 m high. There is small cupola at the top, which was used as the platform to announce the arrival of monsoons and eclipses.