EYE IN THE SKY

Telescope was invented by accident though there are many theories attached to it. In 1655 an unknown European spectacle maker had testified that his father had invented the telescope as early as 1590. As a child he saw the nearby church very close and bigger while playing with two types of glasses. He ran to his father who was also a spectacle maker in excitement and he fixed the glasses that way which was believed to be the first telescope in the world.

But a unique large telescope that focuses light with a slowly spinning bowl of liquid mercury instead of a solid mirror has opened its eye to the skies above India this month in the Himalayas. Such telescopes have been built before, but the 4-meter-wide International Liquid Mirror Telescope (ILMT) is the first large one to be purpose-built for astronomy, at the kind of high-altitude site at Devasthal Observatory. When a bowl of reflective liquid mercury is rotated, the combination of gravity and centrifugal force pushes the liquid into a perfect parabolic shape, exactly like a conventional telescope mirror— but without the expense of casting a glass mirror blank, grinding its surface into a parabola, and coating it with reflective aluminum.

Staring straight up, the rotating mirror will see a swath of sky almost as wide as the full Moon while Earth’s rotation scans it across the heavens from dusk to dawn. Objects appear as long streaks in the image; the separate pixels can be added together afterward to create a single long exposure. Because the telescope sees roughly the same strip of sky on successive nights, exposures from many nights can be added together to get extremely sensitive images of faint objects.

Alternatively, one night’s image can be subtracted from the next’s to see what has changed, revealing transient objects such as supernovae and quasars, the bright hearts of distant galaxies that wax and wane as super massive black holes consume matter. A study suggested as many as 50 lenses might be visible in ILMT’s strip of sky.

Conventional survey telescopes, such as the Zwicky Transient Facility in California and the upcoming Vera C. Rubin Observatory in Chile, cover much more of the sky. But they are unlikely to return to the same patch every single night to search for changes. ILMT has the added strength of sitting next to DOT, which is equipped with instruments that can rapidly scrutinize any fleeting objects discovered by its next-door neighbor. This tag-team approach “is more comprehensive, and scientifically richer,” says Dipankar Banerjee, director of the Aryabhatta Research Institute of Observational Sciences, which runs the Devasthal Observatory.

If ILMT becomes a success, the technology could be scaled up to build much larger liquid mirrors on the Moon, an attractive location for future giant telescopes because it is less seismically active than Earth and has no atmosphere.

Source: Himalayan News Chronicle