by S. Prasad Ganti

Very powerful ground based optical telescopes are found mostly in Chile and Hawaii. Some in the Canary Islands. There is an observatory nestled in the foothills of Himalayas in an Indian town called Nainital. Called ARIES (Aryabhatta Research Institute of Experimental sciencES) and located about 7000 feet above sea level, getting about 200 clear nights a year on an average, it is a good site for optical astronomy. Thanks for the pointer which Surabhi has provided, I did not know of this scientific institution before. 

Named for Aryabhatta, an Indian astronomer and a mathematician who lived in the fifth and sixth centuries AD. Aryabhatta lived before the Islamic golden age when the mantle of mathematics was carried forward by the Arabs. Incidentally, India’s first satellite launched in 1975 was also named in Aryabhatta’s honor. 

The observatory was established more than fifty years back on Manora peak near Nainital. Starting with smaller telescopes, bigger ones were set up as time progressed. Due to the increasing light pollution as the town of Nainital grew, the new location about 15 miles away as the crow flies, about 35 miles away by road, Devasthal (meaning God’s place) was developed. Two such latest telescopes are established in Devasthal. Both these facilities, along with their telescopes, are managed by ARIES.

The 3.6 meters reflector telescope called DOT (Devasthal Optical Telescope) saw the first light in 2016. It is considered as the largest reflector telescope in Asia. The optics has been built in collaboration with the Belgian firm Advanced Mechanical and Optical System (AMOS). It features an optical spectrograph, a CCD imager and a near-infrared spectrograph. The telescope also has active optics containing a wavefront sensor and pneumatic actuators which compensates for small distortions in the shape of the 4.3 tonne mirror due to gravity or atmospheric aberrations. The picture shown below, courtesy ARIES, shows the DOT housed in a dome. 

Second telescope is the 4 meter International Liquid Mirror Telescope (ILMT). It saw its first light recently in May 2022. It has a dish containing a reflecting liquid metal, which is essentially mercury. This dish sits on an air bearing. I never heard of such a liquid based telescope before. Given below is the picture, courtesy ARIES, of the liquid dish with a protective cover.

This telescope is ​very ​useful ​for ​gravitational ​lensing ​studies ​as ​well ​as ​for ​​extragalactic ​objects like quasars, supernovae, galactic clusters etc. The picture given below, courtesy ARIES, shows a few galaxies with NGC 4274 in the top right corner. Gravitational lensing means that an object behind a massive object will present itself as a displaced image like a ring around the foreground object, or shifted to the right or left of the foreground object. Gravity bends the light coming from the background object and causes these distortions.

Although these telescopes pale in comparison with the 8-10 meter telescopes of Chile and Hawaii, there is a clear progression towards bigger and sophisticated telescopes. The future does bode well. Given the international collaborations happening with ARIES, consortiums could build bigger telescopes in the Himalayas. The altitude and the geography are comparable to Hawaii and Chile. And another place to add to my bucket list to visit !