Context: Recently, India commissioned its first liquid mirror telescope in the state of Uttarakhand.

About ILMT

• The telescope is located at an altitude of 2,450 metres at the Devasthal Observatory campus of the Aryabhata Research Institute of Observational Sciences (ARIES) in Nainital, Uttarakhand.
• ARIES is an autonomous institute under the Department of Science and Technology, Government of India.
• The telescope has been built by a collaboration of scientists from Canada, Belgium and India.
• The telescope was designed and built by the Advanced Mechanical and Optical Systems (AMOS) Corporation and the Centre Spatial de Liege in Belgium.
• Purpose: The telescope will help in surveying the sky, making it possible to observe several galaxies and other astronomical sources such as supernovae and record the presence of space debris or meteorites just by staring at the strip of sky that passes overhead. 
• Note: ILMT will be the third telescope to be operating from Devasthal after the 3.6-metre Devasthal Optical Telescope (DOT) — the largest in India commissioned in 2016 — and the 1.3-metre Devasthal Fast Optical Telescope (DFOT) inaugurated in 2010.

Working

• The telescope employs a 4-meter-diameter rotating mirror made up of a thin film of liquid mercury to collect and focus light.
• A large pool of mercury placed in a vessel is spun around so fast that it curves into a parabolic shape.
• Since mercury is reflective, this shape helps in focusing the reflected light.
• A thin sheet of mylar protects the mercury from the wind.
• The telescope, having a primary mirror that is liquid, cannot be turned and pointed in any direction.
• It “stares” at the zenith and watches the sky as the Earth rotates, thereby giving a view of different objects.
• The telescope will electronically compensate for the drift created in the oridnary camera caused due to the rotation of the earth.
• This mode of operation increases observing efficiency and makes the telescope particularly sensitive to faint and diffuse objects.