Jantar Mantar

A Jantar Mantar (Hindustani pronunciation: [d͡ʒən̪t̪ər mən̪t̪ər]) is an assembly of stone-built astronomical instruments, designed to be used with the naked eye.

All were built at the command of the Rajah Jai Singh II, who had a keen interest in mathematics, architecture and astronomy.

The largest example is the equinoctial sundial belonging to Jaipur's assembly of instruments, consisting of a gigantic triangular gnomon with the hypotenuse parallel to the Earth's axis.

The instrument can be used with an accuracy of about 20 seconds by a skilled observer to determine the time of day, and the declination of the Sun and the other heavenly bodies.

The primary purpose of the instruments was to compile astronomical tables and to predict the times and movements of the sun, moon and planets.