Jantar Mantar is a renowned observatory built in the year 1737 by the Maharaja of Jaipur named Jai Singh. It is located on the roof of Man Mahal Palace which was situated on the western bank of river Ganga near the famous Dashashwamedh ghat. Jantar Mantar at Varanasi is a replica of other observatories at New Delhi , Jaipur, Ujjain and Mathura. Raja Jai Singh was an ardent follower of astronomy and before starting the construction, he sent his scholars abroad to study the foreign observatories. Also known as Yanthra Mandir, it was built to measure the local time, sun's declination, altitude, the declination of stars, planets and to determine eclipses. It is endorsed with many instruments to record the position, speed and motion of the planets and stars. Digansha Yantra, Krantivritta Yantra, Dhruva Yantra and Prakash Yantra are some among the instruments used here. Indian Astronomical theories and calculations are experienced at Jantar mantar which is a striking spot for the astronomers, scholars, engineers, architects and scientists.