A narrow black top road from Leh to Hanle runs along the mighty Indus. The road follows the river for 210 km up to Loma, where after crossing a bridge, it turns south and enters the Hanle valley at Rongo. The Hanle valley is unique with neither snow nor rain, despite its cold climate. This is Nature’s gift, as the other routes to Hanle from Srinagar via Kargil and Zojilla pass or via Simla, Manali and Upshi are snowbound except from June to October. Thus any times access is possible only from Leh. The Leh-Hanle road is, however hazardous, too narrow at places with overhanging rocks too low for safe passage of trucks.
The Government of India chose the Indian Institute of Astrophysics to prepare a detailed project report after selecting a suitable site for an infrared and optical telescope in the Himalayas. Fifty man-years of effort went into the site selection spread over two years. It was a national effort involving several agencies. Twenty astronomers by rotation led the search. The result was one of the best project reports ever prepared.
There was the customary procedural roadblock, an evaluation committee. As expected, the negatives were highlighted. In the hot seat was astronomer Ramanath Cowsik assisted by his colleagues, who were back after a strenuous trek. He chose not to respond and admitted the negative points, which were precisely the challenge to he addressed. The difficulties were a test of their commitment, if India wants to have the world’s highest optical telescope. The project report spoke volumes addressing all the concerns. The telescope project was cleared.
The next challenge was moving the 20-tons equipment uphill. The transport of the equipment from the Mumbai docks was meticulously planned and the Indian Air Force planes moved them from Chandigarh to Leh promptly. The Border Roads Organisation, the Army, the Field Research Laboratory and the State Government of Jammu and Kashmir all played a key role in Operation Hanle.
It was an unusually hot summer. The snow in the upper reaches had melted and a flooded Indus forced a delay. The patience was worth it, and the delicate equipment was finally in place in August 1999. It was commissioned within a month. On the night of 26-27 September 1999, the telescope saw the ‘first light’—an astronomer’s dream date for a new telescope. Prof Yash Pal, Chairman of the project Management Board, who was a special invitee, was overjoyed, as the telescope was turned to image the star, Beta Casiopeiae.
The Indian Astronomical Observatory was born in the Himalayas. It was as expected an ideal place to observe the stars, as the smaller overburden of air there absorbs less of the starlight without deflecting it. And the precipitable water vapour is substantially less than in most other sites—a factor favouring infrared astronomy
The road to Hanle is a monument to the country’s resolve to aim at the highest intellectual pursuits in line with its great traditions, even as it addresses the equality important goal of economic uplift. When one realizes that the two goals –intellectual and economic—are not contradictory, travel to Hanle becomes all the more meaningful.
Characteristics that make Hanle a world class astronomical sites—
Accessibility: Leh-Hanle road open throughout the year.
Elevation above means sea level: about 4,517 m
Number of spectroscopic nights: about 250 per annum
Number of photometric nights: about 170 per annum
Precipitable water vapour in the atmosphere : less than 2mm
Annual precipitation of rain and snow : less than 9 mm seeing: Typically more than 1 arcsecond
Distribution of useful nights: Uniform distribution through the year
Location advantage: In the middle of a large lacuna in Astronomical facilities between Canary Islands (20ºW) and Eastern Australia (157ºE)
Ambient temperature and humidity: Low and very low, respectively
Median Wind speed at night: 2.2 m/s (8 kmph)
Man-made disturbance such as pollution, aerosols, smoke etc. Nil