Indian Astronomical Observatory, Hanle
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 in the vast Nilamkhul Plain in the Hanle Valley of Changthang, Ladakh (4250m above msl), the site is a dry, cold desert with 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.
A 2-m optical infrared telescope is installed at the observatory. This telescope is remotely operated from CREST, Hosakote, using dedicated satellite links. A 0.70m wide field robotic telescope is under installation for monitoring transients, under the GROWTH project. IAO also hosts several site monitoring instruments such as seeing monitor, extinction monitor, all sky camera, Automated Weather Station, etc. The site is being characterised for a 10m class telescope.
The infrastructure developed by IIA at IAO, Hanle, has paved way towards initiating many new projects in astronomy such as the gamma-ray array telescope (HAGAR), jointly undertaken by IIA and TIFR and imaging Cherenkov telescope (MACE) undertaken by BARC, as well as in other paradigms of science.
The Hon'ble Chief Minister of Jammu and Kashmir, Dr Farooq Abdullah inaugurated the satellite communication link on Mt. Saraswati, Indian Astronomical Observatory, Hanle on June 2, 2001
The 2m telescope was dedicated to the nation on 29 August 2001 .
IAO Sky Conditions
Seeing
The Differential Image Motion Monitor (DIMM) is considered one of the best methods to explore the integrated effect of the turbulent atmosphere. A robotic DIMM seeing monitor is operational from 31st January 2023 at the proposed NLOT site.
Learn more about IAO DIMM here
SQM
The Sky Quality Meter (SQM) measures the brightness of the night sky in magnitudes per square arcsecond. Automated and operational at IAO Hanle 32:46:47“N 78:57:45“E, 4547m amsl.
Learn more about IAO SQM System here [external link]
Recent IAO Seeing & SQM
IAO Seeing Monitor
IAO SQM
Indian Astronomical Observatory Site
Digpa-ratsa Ri, Hanle, was chosen as the prospective site for a National Observatory after a study of meteorological conditions over the Indian subcontinent, study of topographic maps of high-altitude areas in the Himalayan and trans-Himalayan regions, and a simultaneous reconnaisance 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 1994 December. Detailed characterization of the site began in January 1995, and has continued till date.
The highest peak in Digpa-ratsa Ri is at an altitude of 4517 meters, and has been renamed Mt. Saraswati after the Hindu Goddess of learning. The surrounding Nilamkhul Plain is at an altitude of 4240 meters above 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 meters. The location of the 2-m Himalayan Chandra Telescope (HCT) is to the east of the peak at an altitude of 4500 meters above msl.
The background of the early site survey and results are published in Bull. Astr. Soc. India, 24, 859-869, 1996, and Proc. XIX Meeting of the ASI. 1999 Feb 1-4. The extinction and night sky brightness estimates based on data obtained since the 2m HCT was released for observations in 2003 are published in Bull. Astr. Soc. India, 36, 111-127, 2008.