The Hale Telescope at the Palomar Observatory of the California Institute of Technology, USA.
From the outside a telescope observatory is dominated by the dome that contains and protects the telescope. The images below show the telescope itself (left) and its 200 inch, 14.5 ton mirror (right), removed from the telescope for re-surfacing with aluminium:
The Hale Telescope is used on average about 300 nights a year. Even with weekly cleanings, mirrors periodically need to be given a new coat of reflective aluminum. The old layer of aluminum is removed with an acid wash, exposing the mirror's support structure (below left). The supports prevent gravity from distorting the shape of the mirror no matter which way it is pointed.
The mirror is placed into a heated vacuum chamber and coated with a few grams of vaporized aluminum giving a layer only 1 millionths of a centimetre thick. The images on the right show the mirror before (top) and after re-coating (bottom).
Caltech Astronomy, Palomar Observatory (2004) Re-Aluminization of the 200-inch Primary Mirror of the Hale Telescope at the Palomar Observatory. http://www.astro.caltech.edu/observatories/palomar/alum_mirror/aluminization.htm (accessed 20 September 2004)