Jantar Mantar was constructed by Maharaja Sawai Jai Singh II between 1727 and 1734. The word jantar means instrument, whereas mantar refers to formula or calculation. Situated in Jaipur, this monument is one of the five astronomical observatories present in India. The other four astronomical observatories are located at Delhi, Varanasi, Mathura and Ujjain.Placed adjacent to the city palace, this monument has been awarded as the largest stone observatory in the world. Jantar Mantar also includes about 15 astronomical instruments of various geometrical shapes and sizes. These instruments are used for measuring time, accurately determining the celestial altitude and predicting the occurrence of eclipses. In 1948, Jantar Mantar was declared as a national monument of India.