IAO Hanle: a promising astronomical observatory


The Indian Astronomical Observatory (IAO) located at Hanle near Leh in Ladakh is emerging as one of the most promising observatory sites globally, according to a recent study.

This is due to its benefits of clearer nights, minimal light pollution, background aerosol concentration, extremely dry weather conditions and uninterrupted monsoon, the Science and Technology Ministry said.

Indian researchers and their collaborators conducted a detailed study of the fraction of nocturnal cloud cover at eight high-altitude observatories, including three in India, DST said.

The researchers used combined assimilation and observation reanalysis data spanning 41 years, as well as 21 years of data from satellites. The study classified the quality of observable nights for different astronomical uses like photometry and spectroscopy on a daily basis.

Eight observatories

They analyzed data sets for the Indian Astronomical Observatory (IAO) in Hanle and Merak (Ladakh) and Devasthal (Nainital) in India, the Ali Observatory in the Tibet Autonomous Region of China, the Great South African Telescope in South Africa, the Atacama Observatory of the University of Tokyo. and Paranal in Chile, and the National Astronomical Observatory in Mexico.

The team discovered that the Hanle site which is as dry as the Atacama Desert in Chile and much drier than Devasthal and has around 270 clear nights per year and is also one of the emerging sites for optical astronomy. infrared and submillimeter. This is because water vapor absorbs electromagnetic signals and reduces their strength, the DST said in a statement. The research led by Dr Shantikumar Singh Ningombam of the Indian Institute of Astrophysics (IIA), Bengaluru, and scientists from the Aryabhatta Research Institute of Observational Sciences (ARIES) in Nainital, a DST institute and collaborators from St. Joseph’s College, Bengaluru, and the National Institute of Meteorological Sciences, South Korea, University of Colorado and Chemical Sciences Laboratory, NOAA, US has been published in the Monthly notices for the Royal Astronomical Society.

They found Paranal, located in a high altitude desert in Chile, to be the best site in terms of clear skies with around 87% clear nights in a year. The IAO Hanle and Ali observatories, located about 80 km from each other, are similar in terms of a clear night sky.

They found that Devasthal has a slightly higher number of clear nights compared to other sites on the subcontinent, but is affected by monsoons for about three months per year. However, nocturnal observations at IAO Hanle from the 2m Himalayan Chandra Telescope (HCT) are possible throughout the year without any interruption due to the monsoon.

Due to the benefits of clearer nights, minimal light pollution, a concentration of background aerosols, extremely dry atmospheric conditions and an uninterrupted monsoon, this region is becoming one of the promising sites globally. for the next generation of astronomical observatories, he said.

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