A 4-metre liquid mirror telescope with a retractable roof (left) sits next to two optical telescopes in the Indian Himalayas Jean Surdej
ATOP an Indian mountain sits a 4-metre-wide reflecting basin, its ripple-free surface mirroring everything above it. It is as if someone scooped up a piece of the Bolivian salt flats, the world’s largest natural mirror, and put it in the Himalayas. But unlike South America’s Salar de Uyuni, where the salt plains covered by water produce incredible reflections that draw many sightseers, the basin on the mountain is filled with liquid mercury. And this is no tourist hotspot: it can only be accessed by a small group of scientists who use it to observe the heavens.
The basin is part of a unique telescope. Situated in an observatory in the northern Indian state of Uttarakhand, the International Liquid Mirror Telescope (ILMT) uses the pool of shiny metal to gather light from the skies.
Such telescopes have benefits over conventional ones. Most importantly, they are much cheaper to build. But although the idea of a liquid telescope has been around for centuries, creating a viable one has proven fiendishly tricky. The ILMT was in the works for more than a decade. This year, it opened its eye for the first time. It is the largest of its kind, and the first built to carry out astronomical observations.
The telescope scans the night sky in the hope of spotting new phenomena – when it isn’t raining, that is. But astronomers hope the potential of these devices will one day reach far higher than…
