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The Udaipur Solar Observatory (USO) is located in the historic city of Udaipur, Rajasthan in India on an island in the Fatehsagar lake. The observatory is among the few in the world that are situated on an island. The sky conditions at Udaipur are quite favourable for solar observations. Since the observatory is situated amidst a large mass of water, air turbulence which occurs due to ground heating by sun's rays is decreased. This improves the image quality and seeing (average between 1-2 arc seconds). This observatory was built by Dr. Arvind Bhatanagar following the model of Solar Observatory at Big Bear lake in Southern California.

Utilizing a variety of telescopes, USO is known for its high quality solar observations, which include high-resolution solar chromospheric, magnetic field, velocity, and spectral observations, for studies pertaining to solar flares, mass ejections, and the evolution of solar active regions. USO also fills the large longitudinal gap between Australia and Spain, and provides a link for continuous solar coverage in many international collaborative programs, including the Global Oscillations Network Group (GONG). Since 1981, USO has been managed by the Physical Research Laboratory, Ahmedabad, for the Department of Space, Government of India.

The city of Udaipur was planned around a set of man-made lakes created from rain water. However with population pressure and with poor rainfall, the water in these lakes has been steadily dwindling. In 1975, Fathesagar flooded its adjoining neighborhoods; In 2003, it was completely dry, and one could walk to the USO. See the photo. As of 2006, the lake is full again and you need to take a boat to go to the observatory.

USO in December 2002