International Liquid Mirror Telescope (ILMT)


  • The four-meter International Liquid Mirror Telescope (ILMT) saw the first light recently, gazing out from its vantage on Devasthal, a hill in Uttarakhand.

About International Liquid Mirror Telescope (ILMT)

  • The telescope has been built by a collaboration of scientists from Canada, Belgium and India.
  • It is located at an altitude of 2,450 metres on the Devasthal Observatory campus of the Aryabhata Research Institute of Observational Sciences (ARIES) in Nainital district.
  • 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.

    International Liquid Mirror Telescope (ILMT)
    Source: Wikipedia
  • Nearly 50 litres of mercury, weighing close to 700 kilograms, is spun hard to form a paraboloid mirror of just 4 mm thickness and a diameter of about 4 metres.
  • A thin sheet of mylar protects the mercury from the wind.
  • Once it starts making observations, the telescope will collect gigabytes of data, which will need to be analysed using artificial intelligence and machine learning (AI and ML) tools.
  • The telescope will make sky surveys possible and obtain images that can help observe transient phenomena.
  • It will help analyse events such as supernovae and record the presence of space debris or meteorites — basically, watch the skies.

How is it different from a conventional telescope?

  • A conventional telescope is steered to point towards the celestial source of interest in the sky for observations. The liquid-mirror telescopes, on the other hand, are stationary telescopes that image a strip of the sky which is at the zenith at a given point of time in the night. In other words, a liquid-mirror telescope will survey and capture any and all possible celestial objects — from stars, galaxies, supernovae explosions, asteroids to space debris.
  • Conventional telescopes have highly polished glass mirrors — either single or a combination of curved ones — that are steered in a controlled fashion to focus onto the targetted celestial object on specific nights. The light is then reflected to create images.
  • As opposed to this, as is evident by the name, the liquid-telescope is made up of mirrors with a reflective liquid, in this case, mercury — a metal which has a high light-reflecting capacity. About 50 litres (equal to 700kgs) of mercury filled into a container will be rotated at a fixed constant speed along the vertical axis of the ILMT. During this process, the mercury will spread as a thin layer in the container forming a paraboloid-shaped reflecting surface which will now act as the mirror. Such a surface is ideal to collect and focus
    light. The mirror has a diameter of 4 metre.
  • Another difference between the two is their operational time. While conventional telescopes observe specific stellar sources for fixed hours as per the study requirement and time allotted by the respective telescope time allotment committee, ILMT will capture the sky’s images on all nights — between two successive twilights — for the next five years starting October 2022.
  • For protecting it from moisture during monsoon, the ILMT will remain shut for operations between June and August.

Which countries are involved in its development?

  • India, Belgium, Canada, Poland and Uzbekistan are the main countries who have collaborated to set up the ILMT. The telescope was designed and built at the Advanced Mechanical and Optical Systems Corporation and the Centre Spatial de Liège in Belgium.


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