Service and Mirror Aluminization

On November 11 – 21, the Hale Telescope will be serviced and its primary mirror aluminized. First, the instrument and cage at the bottom of the telescope are removed, exposing the mirror cell. With the cell lowered, an acid wash is used to strip off the old layer of aluminum. Then, the aluminization chamber is placed over the mirror. Inside the chamber, hundreds of tungsten coils draped on aluminum are heated to vaporize the aluminum, which then coats the mirror with a thin film—a successful coating deposits just a few grams of aluminum across the 200-inch disk making a layer only 3 millionths of an inch thick.

The 200-inch mirror before and after aluminization. The Hale telescope, used on average 300 nights a year, periodically requires cleaning and a new coat of reflective aluminium. This process takes a few days and is performed approximately every two years. (Palomar Observatory)