Indian Astronomical Observatory, Astronomical observatory in Hanle, India.

The Indian Astronomical Observatory stands on Mount Saraswati, Digpa-ratsa Ri, at Hanle in south-eastern Ladakh, at an elevation of 4,500 metres. Its main building is a tall cylinder clad in vertically ribbed white and grey metal panels, topped by a single hemispherical dome of shiny silver metal divided into rectangular panels, with a thick curved band arcing over it. A lower wing with a sloped corrugated metal roof and small windows extends to the left, and an entry door sits on the right face.

Operations began in 2001 and marked the country's entry into high-altitude sky research with advanced equipment. The site choice followed years of searching for a place with low humidity and minimal light pollution.

The observatory's name is tied to Hanle, whose six hamlets—Bhok, Dhado, Punguk, Khuldo, Naga and a Tibetan refugee habitation—lie within the 1,073 sq km dark-sky preserve declared in September 2022. Villagers live under restrictions meant to keep the night dark: indoor-only lights in places, light-blocking curtains, yellow street lamps and no high-beam headlights.

Visitors need a permit and should spend several days adjusting to the altitude beforehand to avoid discomfort. Warm clothing is essential because of the harsh climate and low temperatures even during summer months.

The location in the Changthang highland plateau allows over 255 clear nights per year, ranking among the best conditions worldwide. The dry air and dark sky enable measurements of faint cosmic signals that are barely visible elsewhere.