New mirror coating on the LBT

How do you make telescope mirrors so shiny bright?

Large astronomical telescopes use mirrors, rather than lenses to gather light.  The large mirrors are coated with a very thin layer of metal, say aluminum.  All the big glass does is hold this thin reflective coating in place.

For a nice diversion, watch the movie below of the recoating process for one of the mirrors at the Large Binocular Telescope.  The coatings are done in place.  First, the old coating is scrubbed off, and then a large vacuum jar is placed over the mirror.  Air is pumped out, and evaporated metal is sprayed on.

Credit:  Matthieu Bec, LBT

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