Hanle was chosen as a prospective site for setting up telescopes in India, as it fulfilled all the requirements of the astronomers. As mass motions of air would change the nature of the atmosphere over the site, astronomical seeing conditions or blurring were evaluated by using a differential image motion monitor. In addition, a winter reconnaissance visit was undertaken.
Professor Tushar Prabhu and other experienced astronomers of IIAP set up a permanent camp at Hanle, availing themselves of the hospitality of the Indo-Tibetan Border Police and monitored the skies and atmospheric conditions every hour. It was a demanding assignment in the cold and dry place but the very ambience of the place delighted the astronomers. Hanle was found to be one of the best sites in the world, compared to Mauna Kea (Hawaii), Atacama and Antarctica, for optical, infrared and gamma ray astronomy. Still, many in India dissuaded the astronomers from proceeding ahead, claiming that the telescope at Hanle was simply not practical. But the pioneers persisted.
A factor worthy of appreciation is the positive contribution in favour of Hanle made by the people of the Ladakh region, represented by the Ladakh Autonomous Hill Development Council, formed in 1995 in the wake of a democratic wave in the region. Unlike Atacama in Chile, Hanle has people around, though in small numbers, living there for generations. Those who wondered whether the people would cooperate in a project that placed weighty machines near the pristine peaks were in for a surprise. The people of Ladakh readily co-operated in the national effort. Watching the construction of the telescope at Hanle, the Chinese across the border saw the advantage of the region for astronomical studies and identified a site for an optical telescope, about 100 km east of Hanle in their territory.
Once Hanle was chosen, it was obvious that the extreme weather and negligible infrastructure would pose a formidable barrier to day-to-day operations. Fortunately, technology came to the rescue. India by then had its own domestic satellite in operation that can be used to operate the distinguished space scientist, Dr. K. Kasturirangan, studied the proposal for a satellite link between Hanle and a control center to be set up near Bangalore and recommended the link. That decision made a big difference to the success of Hanle.
It is one of those projects which caught the imagination of the decision-makers at the State level too. Perhaps a telescope, aimed at celestial beauty and wonder offered a symbol of relief and hope from the every day problems on the ground. The then Governor Gen. Krishna Rao and the former Chief Minister of Jammu & Kashmir Dr. Farooq Abdullah, took a keen interest in its early completion the J & K government gave 320 hectares at Hanle. In fact, the government cooperated in the preparatory work for the transfer of the land, anticipating the formal approval by the Central government.
Several central government departments (such as Space Telecommunications), besides the Army and the Border Roads Organization cooperated in setting up the telescope. In September, 2000, the Observatory was commissioned after which extensive performance tests were undertaken. In September 2001 the observatory was dedicated to the nation, after the remote operation by satellite was in place.
The telescope was called the Himalayan Chandra Telescope, in honour of a great son of India, Subrahmanyan Chandrasekhar, the renowned astrophysicist and Nobel Laureate. The Scorpion Mount peak too was renamed as Mount Saraswati, after the Hindu goddess of learning and the now invisible river at the confluence of the Ganga and Yamuna at Allahabad.
Hanle is an astronomer’s paradise! The basic reason is simply its location and altitude. It is one of the driest places in India. The column of atmospheric water vapour over Hanle is less than 1.5 millimetres, as against 25 mm at sea level. The air pressure is 590 millibars with 40 per cent of the atmosphere below the telescope’s location. Hanle has 150 to 180 cloud-free nights; in fact over 260 nights are useful for observation, when more than half the sky is clear.
Access to Hanle is now relatively easy. A direct air link from Delhi is available to Leh, 250 km away. However, there is a catch; lack of normal levels of oxygen. A visitor has to undergo a period of acclimatization for about five days, first by simply lying on a cot and then slowly venturing out. A normally healthy person’s body gets adapted to the environment in a remarkably short time, despite some initial headache. But if one has any breathing problems, it gets aggravated! Prolonged stay at that altitude is not medically recommended.
The Observatory, at 78º57’ (minutes) 5.1” (seconds) East longitude and 32º46’46” North latitude, is midway between the astronomical facilities on the east coast of Australia (longitude 160 deg East) on the one side and Canary Islands in the Atlantic Ocean (longitude 20 deg West) on the other. The area between the two telescopes covers about 180º. As the Earth rotates, astronomical objects rise above the horizon at a particular time and set after about 12 hours. The intensity of the emitted radiation can be measured only when the astronomical object is high in the sky for about six hours each day and that too if the star rises and sets at night.
If a star’s variation time is more than six hours, many telescopes, located in different continents, have to be involved in continuous monitoring. When an astronomical object sets below the western horizon in Australia, it would rise above the eastern horizon in India. Some eight hours of observation of celestial phenomena could be had before the European telescopes at La Palma on the Canary Islands could see them. When it sets at La Palma, it can be seen by observatories in America and then the Australian observatories can see it again. The Himalayan Chandra Observatory could thus play a crucial role in the ongoing worldwide effort to observe astronomical events. In fact, the telescopes at Hanle and Atacama (Chile) are also complementary; when it is day in Atacama, it is night in Hanle. Again, Atacama sees more of the southern sky, whereas Hanle can look at the north hemisphere. Hanle is ideal for astronomy, not only in the visible band but also in the infrared and high-energy gamma rays.