The universe in swirling mercury

Like a gentle giant awakening from a slumber, a new telescope, coming up at Devasthal, in Uttarakhand, will open its 'eye' and receive its first light sometime in April 2022. The eye - its mirror - is an unconventional one: it's made not of silvered glass, but of swirling mercury. And rather like someone with a crick in the neck, it can only look in one direction: straight up, at the zenith. However, it is a very low-cost telescope - and so adaptable that experts reckon that one can be put on the far side of the Moon. And if it proves successful, the 4-metre International Liquid Mirror Telescope (ILMT) - the outcome of a collaboration among Belgium, Canada, India, Poland, and Uzbekistan - could well stir things up in the starry-eyed world of astronomy.
 
"The telescope would work in a survey mode, scanning the sky from night to morning," says Dr Brajesh Kumar, a scientist at the Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital. It will observe the night sky in three colour bands. 

"The ILMT can be dedicated to surveying the variable celestial objects in its half-a-degree field of view," says Prof Jean Surdej of the University of Lèige, Belgium, and the principal investigator of the ILMT project. It would discover many transients like supernovae, quasars, and so on, and can help study space debris, he adds. 

The principle behind its functioning is simple (see box: How the mirror sees). Fill a container with mercury and spin it. Owing to gravity and the centrifugal pseudo force, the shiny liquid metal will acquire a paraboloidal surface, considered the ideal shape to focus the light of distant stars. Place a camera at the focal point, and there's your zenith-pointing telescope.