The biggest of five astronomical observatories built by Maharaja Jai Singh during the period 1727-1734 in north India, it is located very close to the City Palace. The observatory consists of fourteen major geometric devices (or yantra in Hindi) for measuring time, predicting eclipses, tracking stars in their orbits, ascertaining the declinations of planets, and determining the celestial altitudes etc. Guides provide fascinating explanations of how each of the instruments work, and how through watching, recording and meticulous calculation, Jai Singh measured time by the place the sun's shadow fell on the huge sundials and charted the annual progress through the zodiac. Each construction has a specific purpose, such as calculating eclipses. The most striking instrument is the sundial, with its 27m-high gnomon; the shadow this casts moves upto 4m per hour. It is 9 kms away from the hotel.