Jantar Mantar, in Jaipur, is the most famous among five observatories built by Sawai Jai Singh II in India. It was built to check the astronomical observation at Jaipur. The Jantar Mantar at Jaipur was conceived as a quest for discovering the mysteries of the Cosmos .The sun dial of Jantar mantar is one of the major tourist attraction. In Sanskrit, 'Jantar Mantar' is used for 'Magical Devices' and it is undoubtedly so with the huge masonry instruments, which were placed here to measure 'the harmony of the heavens'. Conceived by Sawai Raja Jai Singh II, it was completed in seven years from 1727 to 1733.Sawai Jai Singh sent his ambassadors to all parts of the world before starting the construction of this observatory.

 The ambassadors returned with many manuals and ideas on astronomy containing cutting-edge technological information. One of these manuals was a copy of La Hire's "Tables". The king ordered the observatory to be built according to the details contained in this manual. The Observatory Jai Singh had the choice of constructing the observatory either with metal instruments or masonry instruments. The metal instruments, constructed according to the texts of the Islamic school of astronomy, did not measure up to Jai Singh's expectations. He discarded them in favor of the instruments of stone and masonry that he himself designed. 

Instruments in the Observatory 

» Samrat Yantra : Samrat Yantra consists of a massive triangle with a curved structure on both sides. 

» Ram Yantra : It is an instrument used to indicate the altitude and the azimuth or declination of celestial bodies.

» Jai Prakash Yantra : It is used to find out the positions of the celestial bodies during days and nights. It is a two hemispherical bowl structure, which represents the celestial sphere and there is a vertical rod in the center