"Jantar Mantar is an observatory built by Jai Singh, the Maharaja of Jaipur in the year 1737."
Jai Singh was a great admirer of science and technology and he was particularly passionate about astronomy. The Jantar Mantar at Varanasi was built in line with Delhi, Mathura, Ujjain and Jaipur observatories. It was used to measure the local time, the sun's declination, altitude, the declination of stars, planets and to determine eclipses. The Jantar Mantar at Varanasi has several masonry instruments to record the motion, speed and properties starts and planets and study astronomy that are accurate and can still be used efficiently today.