The Indian Astronomical Observatory at Hanle in Leh (IAO-Hanle) has emerged as one of the best observatories in the world with clear night skies round the year, claimed the Ministry of Science and Technology.

The IAO-Hanle observatory has the advantages of more clear nights, minimal light pollution, and background aerosol concentration. The extremely dry atmospheric condition and little interruption by Monsoon have made it a favorite among scientists, the Ministry said.

A team of world-renowned researchers, who studies the best Astronomical Observatories in the world, analysed the data extending over 41 years along with 21 years of data from satellites, found that Indian Astronomical site IAO-Hanle was beset after the Paranal Observatory, located in the high altitude desert in Chile, said a senior officer of the Ministry of Science and Technology.

The researchers found that Paranal, located in a high-altitude desert in Chile, was the best site in terms of clear skies with around 87% of clear nights in a year. However, IAO-Hanle, and Ali observatories, which are located around 80 km from each other, are similar to each other in terms of clear night skies, the Ministry said.

Researchers from India and their collaborators carried out a detailed study of the nighttime cloud cover fraction over 8 high altitude observatories, including three in India. They used reanalysis data, combined from assimilation and observation extending over 41 years, along with 21 years of data from satellites.

The study also classified the quality of observable nights for different astronomical usages like photometry and spectroscopy on a daily basis. The research was conducted by Astronomers, who 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. The high altitude observatories studied by the researchers include the Indian Astronomical Observatory (IAO) in Hanle and Merak (Ladakh), Devasthal Observatory (Nainital) in India, Ali Observatory in the Tibet Autonomous Region in China, South African Large Telescope in South Africa, University of Tokyo Atacama Observatory and Paranal in Chile, and the National Astronomical Observatory in Mexico.

“The team found 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 in a year and is also one of the emerging sites for infrared and sub-mm optical astronomy,” the Ministry said.

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