The Jantar Mantar, New Delhi, is one of five built by Maharaja Jai Singh II of Jaipur, from 1724 onwards, as he was given by Mughal emperor Muhammad Shah the task of revising the calendar and astronomical tables. It consists of 13 architectural astronomy instruments. The primary purpose of the observatory was to compile astronomical tables, and to predict the times and movements of the sun, moon and planets. Some of these purposes nowadays would be classified as astronomy.
Maharaja Jai Singh II of Jaipur constructed five Jantar Mantars in total, in New Delhi, Jaipur, Ujjain, Mathura and Varanasi and they were completed between 1724 and 1735.