Jantar Mantar was built in 1724 by Raja Jai Singh II of Jaipur in Delhi. Jantar Mantar of Delhi is an astronomical observatory with masonry instruments.This ancient monument is one of the five astronomical observatories build by Maharaja Jai Singh II as he was given by Mughal emperor Muhammad Shah the task of revising the calendar and astronomical tables.Jai Singh built four such observatories in Jaipur, Ujjain, Mathura and Varanasi.
Jantar Mantar of New Delhi was built with a view to help the practicing astronomers in observing the movements of the Sun, Moon and all other planets.The observatories are known as Jantar Mantar which derives its name from the corruptions of the words 'yantra' (instrument) 'mantra' (formula) over the period.As the time goes on this is being known as Jantar Mantar. There are four distinct instruments within the observatory of Jantar Mantar: the Samrat Yantra, the Ram Yantra, the Jayaprakasht, and the Mishra yantras.
The whole structure of Jantar Mantar is made of stone and marble with each of then having an engraved astronomical scale. Jantar Mantar finally got the status of a national monument in 1948.Jantar Mantar Observatory in Connaught Place, New Delhi is an integral part of India’s scientific heritage. It has always attracted architects, historians and scientists from all over the world.
Once a harbinger of scientific era and an epitome of inventiveness in field of astronomy, Jantar Mantar has lost its sheen as an instrument of measurement; the reason being construction of building around the structure which hinders the process of accurate observations.