About Primary Telescope Mirrors

Primary telescope mirrors are the most important element in astronomy equipment. The bigger they are the more difficult it is to make and achieve accurate results. The best material needed to make a mirror is glass. Glass is unique in that it will not be affected by changes in temperature.

The surface of the primary mirror used for telescopes is slightly curved. This is known as concave. It takes between 6 and 9 months to grind the glass to produce the right curve. The glass must be polished extremely smooth, so smooth that any bumps are less than 1/10th of the wavelength of light.

The last polish of the surface is coated with a thin layer of aluminum. This is done so the primary mirror is extremely reflective. The coating is used for 2 years and is only 10 atoms thick. The mirror is removed from the telescope and the old coating is removed and a new layer of aluminum is placed using a special mirror coating.