TIL some large telescopes use liquid mercury for a reflective mirror instead of glass. The rotating liquid assumes the paraboloidal shape regardless of the container's shape and has a much lower cost than traditional glass mirrors.

http://en.wikipedia.org/wiki/Liquid_mirror_telescope



Submitted January 27, 2015 at 10:50PM by TRAVICEW http://www.reddit.com/r/todayilearned/comments/2tux7f/til_some_large_telescopes_use_liquid_mercury_for/