The Indian Astronomical Observatory, the high-altitude station of IIA is situated at an altitude of 4500 metres above mean sea level to the north of Western Himalayas. Atop Mt. Saraswati / Digpa Ratsa Ri in the vast Nilamkhul Plain in the Hanle Valley of Changthang, Ladakh (4250m above MSL), the site is a dry, cold desert with a sparse human population and the ancient Hanle monastery as its nearest neighbour. The cloudless skies and low atmospheric water vapour make it one of the best sites in the world for optical, infrared, sub-millimetre, and millimetre wavelengths.
The Himalayan Chandra Telescope (HCT) is a 2-m optical and near-infrared telescope installed at the observatory. This telescope is remotely operated from CREST, Hosakote (in Karnataka), using dedicated satellite links. The 2m telescope was dedicated to the nation on 29 August 2001. The GROWTH India Telescope, a 0.70m wide field robotic telescope also functions from the same site as a part of the global GROWTH network and is used for monitoring transients, in collaboration with IIT Bombay. IAO also hosts a newly refurbished 50 cm telescope and several site monitoring instruments such as a seeing monitor, extinction monitor, all-sky camera, Automated Weather Station, etc. The site is also being characterized for a large observatory-class telescope.
The infrastructure developed by IIA at IAO, Hanle, has paved the way towards initiating many new projects in astronomy such as the gamma-ray array telescope (HAGAR), jointly undertaken by IIA and TIFR and the imaging Cherenkov telescope (MACE) undertaken by BARC. Both HAGAR and MACE are a lower elevation of 4250 m above MSL.