What is a liquid mirror telescope?

How do these high-tech mirrors use the likes of liquid mercury to see the stars?

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The six-metre diameter Large Zenith Telescope at the University of British Columbia in Canada is the world’s largest liquid mirror telescope.

Liquid mirror telescopes work in a similar manner to regular telescopes, apart from the use of a liquid as the source of light collection. Most liquid mirrors use mercury to obtain accurate views of the night sky. This is poured into a rotating dish, several metres in diameter.

As the dish rotates it forces the liquid into a parabola, raised at the edges. The force of gravity pulls the liquid down while the inertia from the rotation pulls the liquid sideways, giving a curved surface about 1mm thick. If the liquid is disturbed, the continued rotation of the mirror brings back its parabolic shape. As light is incident on the liquid mirror it is focused into a secondary non-liquid mirror, where the image is collected. Liquid mirror telescopes can only be pointed vertically upwards in the zenith position, so they are mainly used to observe the passing night sky, but they are much cheaper than their solid mirror siblings.

Image courtesy of Paul Hickson, University of British Columbia.

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