Sawai Raja Jai Singh II had built solar observatories at five places in India – Ujjain, Jaipur, Delhi, Varanasi and Mathura. The observatory in Ujjain, popularly known as Vedhshala and built between 1723 AD to 1730 AD, is the oldest one and still operational. The observatory (Jantar Manar) serves as authentic instrument to carry out various astronomical studies by Department of Education and every year an ephemeris (Panchang - पंचांग) is published. There is a small planetarium and a telescope to observe the moon, Mars, Jupiter and their satellites. The observatory is also used for weather forecasts. Madhav Rao Scindia, the Maratha Maharaja of Gwalior, renovated it in 1923 AD.
Among the observatories built by Raja Jai Singh, the observatory of Ujjain has great importance in the period of ancient practical astronomy. The Ujjain city was on the Tropic of Cancer. While the positions of Kashi ( Varanasi), Delhi, Jaipur and Mathura cities were towards the north from Tropic of Cancer and still they are in the same direction. On the other hand the position of Ujjain has been changed due to slow diminution every year in the maximum obliquity of the Ecliptic, resulting that the sun goes towards the north from the zenith of the Ujjain. Jantar Mantar was earlier called as Yantra Mandir. It has fascinating masonry instruments which are still in use.