India's First Liquid Mirror Telescope Commissioned In Uttarakhand, Is Largest In Asia

The liquid mirror telescope, which is the largest in Asia, will observe the overhead sky to identify transient or variable objects such as supernovae, gravitational lenses, space debris, and asteroids

Top view of the Indian Liquid Mirror Telescope placed at Devasthal Observatory. The picture shows the liquid mercury mirror covered by a thin mylar film

Source : Department of Science and Technology

India's first liquid mirror telescope has been commissioned atop Devasthal, a hill in Uttarakhand. The liquid mirror telescope, which is the largest in Asia, will observe the overhead sky to identify transient or variable objects such as supernovae, gravitational lenses, space debris, and asteroids. 

The telescope, dubbed the Indian Liquid Mirror Telescope (ILMT), will help survey the sky, and make it possible to observe several galaxies and other astronomical objects just by staring at the strip of the sky above, the Department of Science and Technology (DST), Government of India, said on its website.

The ILMT is a novel instrument built by astronomers from India, Belgium, and Canada, and is equipped with a rotating mirror that has a diameter of four metres. The mirror is made up of a thin film of liquid mercury to collect and focus light.

The telescope has been placed at an altitude of 2,450 metres above sea level, at the Devasthal Observatory campus of Aryabhatta Research Institute of Observational Sciences (ARIES). This is an autonomous institute under the DST and is located in Nainital, Uttarakhand. 

What Is A Liquid Mirror Telescope?

A liquid mirror telescope is a special type of reflecting telescope that uses a liquid as the primary mirror, instead of aluminised glass. The liquid is usually mercury, and is poured into a rotating dish. As a result of the rotation, two fundamental forces — gravity and inertia — act on the mercury.  Inertia is the resistance of an object to its state of rest or motion. The gravity pulls down on the surface of the liquid, while the inertia pulls the liquid sideways at the edge of the dish. 

The causes the liquid to form a uniform and perfect parabola, which is the ideal reflecting surface for a telescope. A liquid mirror telescope surface remains smooth and flawless with little or no maintenance. Also, the gravity and inertia can make the liquid return to its original state if it is disturbed. 

NASA had created a liquid mirror telescope as part of the NASA Orbital Debris Observatory which was located in New Mexico. The telescope, known as the Large Zenith Telescope (LZT), had a mirror with a diameter of six metres, and was located in the University of British Columbia's Malcolm Knapp Research Forest. The LZT was one of the largest optical telescopes in the world. It was decommissioned in 2016, according to online magazine Atlas Obscura.

How Does The Indian Liquid Mirror Telescope Work?

India's first liquid mirror telescope will use mercury as the primary mirror. The scientists from India, Belgium, and Canada spun a pool of mercury to ensure that the surface is curved into a parabolic shape, which is ideal for focusing light. A thin transparent film of mylar has been used to protect the mercury from wind, according to the DST.

The light reflected from the liquid passes through a sophisticated multi-lens optical corrector. This will ensure that sharp images are produced over a wide field of view. The images will be recorded by a large-format electronic camera located at the focus of the telescope.

According to the DST, Paul Hickson from the University of British Columbia said that the rotation of the Earth causes the images to drift across the camera, but the motion is compensated electronically by the camera. Hickson, who is an expert in the field of liquid mirror technology, added that the mode of operation increases the observing efficiency of the telescope and makes it particularly sensitive to faint and diffuse objects.

Dipankar Banerjee, Director of ARIES, said that the ILMT is the first liquid mirror telescope designed exclusively for astronomical observations installed at the Devasthal Observatory.

With the commissioning of the ILMT, the Devasthal Observatory now has two four-metre class telescopes. The other four-metre class telescope at the observatory is called the Devasthal Optical Telescope (DOT). 

The ILMT was designed and built by the Advanced Mechanical and Optical Systems (AMOS) Corporation and the Centre Spatial de Liege in Belgium.