THE TWELVE <italic>RĀŚIVALAYA</italic> INSTRUMENTS AT THE OBSERVATORY OF JAI SINGH IN JAIPUR

The Observatory at Jaipur (popularly known as Jantar Mantar) has many astronomical instruments of the eighteenth century devoted to measurements of time and angles. Most of the instruments are well studied, and the accuracies achieved by these large structures have been analysed in detail. However, the functioning of the 12 sundials designated as <italic>Rāśivalaya</italic> has yet to be understood clearly. Here we report our observations in an attempt to identify the functioning and the purpose of this set of instruments. They can be used for measuring the hour angle, daily motion and the ecliptic latitudes of not only the Sun but also the planets and the Moon.