Science: Taking a Mercurial Approach

Telescopes with liquid mirrors may break the size barrier

The telescope sits on the lawn outside Vachon Pavilion at Quebec's Laval University, its gently concave 40-in.-diameter mirror pointing at the sky. Concentrating and reflecting faint starlight into a camera mounted above it, the gleaming face of the mirror seems devoid of the slightest imperfection; it is so smooth, in fact, that it looks solid.

But that is an illusion. The mirror is really a pool of liquid mercury in a shallow wood container. A touch would send ripples racing across its surface, and it must always aim straight up to retain its curvature. As the container is slowly rotated on...

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