The world’s largest optical telescope starts functioning in India

India’s largest optical telescope that can identify new supernova and asteroids, became operational on Thursday with the unique liquid-mirror instrument getting its “First Light” up in the Himalayas. Located near Nainital at an altitude of more than 8,000 feet (2,450 mt), the four-metre telescope is designed to survey a strip of the sky passing overhead each night, allowing it to identify transient or variable objects such as supernova, gravitational lenses, space debris and asteroids.

Built in collaboration with Belgium and Canada, the Rs 40-crore International Liquid Mirror Telescope was designed and built by the Advanced Mechanical and Optical Systems (AMOS) Corporation and the Centre Spatial de Liège in Belgium, while ARIES offered the site.

“It can identify new transient objects like supernovae explosions and notify other telescopes to follow up. We hope to start regular scientific observations from the winter,” Dipankar Banerjee, director, Aryabhatta Research Institute of Observational Sciences, which is housing the telescope at Devasthal, told DH.

largest optical telescope

Contrary to the conventional telescopes where a glass mirror is used to capture the light, liquid mercury covered by a thin film is used as the mirror. Such telescopes take advantage of the fact that the surface of a rotating liquid naturally takes on a parabolic shape, which is ideal for focusing light. A thin transparent film of mylar protects the mercury from wind.

The reflected light passes through a sophisticated multi-lens optical corrector that produces sharp images over a wide field of view. A large-format electronic camera, located at the focus, records the images. “This is the world’s biggest and only liquid-mirror instrument that can be used for survey. Its limitation, however, is that the instrument can’t be tilted,” said Kuntal Misra, project investigator of ILMT at ARIES.

As soon as the roof of the telescope building opens up, it starts taking pictures, looking straight at the zenith. Since the amount of data it would generate every night would be around 10 GB, ARIES is installing sophisticated data pipelines and algorithms. “The data collected from ILMT will be ideally suited to perform a deep photometric and astrometric variability survey over a period of typically five years” notes project director Jean Surdej, professor at the University of Liège, Belgium and University of Poznan, Poland.

The Devasthal campus at ARIES now houses three telescopes – the ILMT, a 3.6 mt standard optical telescope and a 1.3 mt optical telescope. The institute has a fourth telescope (a small one mt class) at its administrative campus near Nainital town.

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