Jantar Mantar observatory, Jaipur, India. The observatory consists of stone astronomical instruments (yantras), all of which were constructed to allow observation of celestial objects, the measurement of local time, and to predict the times and movements of the Sun, Moon and planets. This relatively small sundial-type structure is one of twelve used to make observations of the zodiac. This site, the best-preserved of five similar sites, was constructed in west-central India between 1724 and 1734 for Maharaja Jai Singh II.