Telescope with a mirror of 50 liters of mercury launched in India


The use of mercury significantly reduces the cost of telescopes

A unique telescope that focuses light using a slowly rotating bowl of liquid mercury instead of a solid mirror has opened its eyes in India, reports Science.org.

The $2 million instrument, built by a consortium of Belgium, Canada and India, is much cheaper than glass-mirror telescopes: not far from it is the 3.6-meter Devastal Optical Telescope (DOT), built by the same Belgian company, but it cost $18 million. Some astronomers believe that liquid mirrors are the ideal technology for building a giant telescope on the moon.

As the bowl of reflective mercury rotates, the combination of gravity and centrifugal force pushes the liquid into a perfect parabolic shape, just like a normal telescope mirror – but without the expense of casting a glass mirror blank, grinding its surface into a parabola, and coating it with reflective aluminum.

Looking straight up, the rotating mirror will see a strip of sky nearly as wide as the full moon, while the Earth’s rotation scans it across the sky from dusk to dawn.

“You just turn it on and off,” astronomers say. Objects appear in the image as long stripes, individual pixels can then be stacked together to create one long exposure.