• Location: Jaipur, Rajasthan
• Famous As: Biggest stone observatory in the world
• Built In: 1716 AD
• Built By: Sawai Jai Singh II

The Jantar Mantar is a collection of architectural astronomical instruments, built by Maharaja (Ruler) Jai Singh II at his then new capital of Jaipur between 1727 and 1734. It is modeled after the one that he had built for him at the then Mughal capital of Delhi. He had constructed a total of five such facilities at different locations, including the ones at Delhi and Jaipur. The Jaipur observatory is the largest of these.

It is said that Sawai Jai Singh II sent his envoys to various parts of the world to collect manuals, astronomical tables and data on the advances made in the fields of astronomy. Sawai Jai Singh II got so much impressed with the La Hire's "Tables" that he ordered that the Jaipur observatory would be built according to the data available in the table manual. After the Jaipur Jantar Mantar was completed, it was discovered that it was even more accurate than the table. The observatory houses the Jaiprakash Yantra, Samrat Yantra, Ram Yantra and the Composite instrument, which comprises of a sundial and a massive hemisphere.

Located near the gate of the City Palace, Jantar Mantar of Jaipur, Rajasthan is the biggest stone observatory in the world, still in a running condition. Make sure to visit this observatory while on a trip to Jaipur.

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.