Editing Primary mirror (section)

==Description==
The primary mirror of a reflecting telescope is a [[Curved mirrors|spherical]], [[Parabolic reflector|parabolic]], or [[Hyperboloid|hyperbolic]] shaped disks of polished reflective metal ([[speculum metal]] up to the mid 19th century), or in later telescopes, glass or other material coated with a reflective layer. One of the first known reflecting telescopes, [[Newton's reflector|Newton's reflector of 1668]], used a 3.3&nbsp;cm polished metal primary mirror. The next major change was to use silver on glass rather than metal, in the 19th century such was with the [[Crossley reflector]]. This was changed to vacuum deposited aluminum on glass, used on the 200-inch Hale telescope.

Solid primary mirrors have to sustain their own weight and not deform under gravity, which limits the maximum size for a single piece primary mirror.

[[Segmented mirror]] configurations are used to get around the size limitation on single primary mirrors. For example, the [[Giant Magellan Telescope]] will have seven 8.4 meter primary mirrors, with the resolving power equivalent to a {{convert|24.5|m|ft|1|abbr=on}} optical aperture.<ref>{{cite magazine |title=Giant telescope in race to become world's largest |date=2007-10-04 |author=Maggie McKee |magazine=[[New Scientist]] |url=https://www.newscientist.com/article/dn12742-giant-telescope-in-race-to-become-worlds-largest.html |access-date=2009-03-27}}</ref>