The Indian Astronomical Observatory located at Hanle near Leh in Ladakh is becoming (IAO) one of the most promising observatory sites globally, according to a recent study. This is due to its advantages of more clear nights, minimal light pollution, background aerosol concentration, extremely dry atmospheric condition, uninterrupted by rains.
Astronomers are constantly searching for ideal locations around the world to build their next big telescope based on local meteorological data collected over many years. Such studies are crucial in planning for future observatories and the prediction of how they will vary with time.
Researchers from India and their collaborators carried out a detailed study of the night-time cloud cover fraction over eight high altitude observatories, including three in India, namely IAO in Hanle, Merak (Ladakh), and Devasthal (Nainital).
Digpa-ratsa Ri, Hanle, was chosen as the prospective site for a National Observatory after a study of meteorological conditions over the Indian subcontinent, a study of topographic maps of high-altitude areas in the Himalayan and trans-Himalayan regions, and a simultaneous reconnaissance survey of six candidate sites in September 1993. Further, visits were made by scientists and engineers of the Institute in January and June, 1994. The permanent site survey camp was established at the edge of Nilamkhul Plain, due north of Digpa-ratsa Ri in December 1994. Detailed characterisation of the site began in January 1995 and has continued till date.
The highest peak in Digpa-ratsa Ri is at an altitude of 45 1 7 metres, and has been named Mount Saraswati. The surrounding Nilamkhul Plain is at an altitude of 4240 metres above mean sea level (msl). The range measures 2 km east-west and 1 km north-south with the top providing about half square km of flat area. The peak contains a few rocky mounds which have been levelled by a few metres. The location of the 2-metre Himalayan Chandra Telescope (HCT) is to the east of the peak at an altitude of 4500 metres above msl.
After examining several years of data of various astro-climatological parametres, IIA installed the 2-metre aperture Himalayan Chandra Telescope (HCT) at IAO, Hanle, in 2000. Thereafter, due to the uniqueness of this site, several astronomical telescopes operating at optical and infrared wavebands have been installed at Hanle by several institutes in the country.