The huge mirror of the Gemini South telescope in Chile just got a fresh reflective coating -- less than two ounces (50 grams) of silver.

Most astronomical mirrors are coated with aluminum. Silver has a greater ability to reflect some types of infrared light compared to aluminum, and Gemini observes in both optical and infrared.

"The main advantage of silver is that it reduces the total thermal emission of the telescope," said Scott Fisher a mid-infrared astronomer at Gemini. "This in turn increases the sensitivity of the mid-infrared instruments on the telescope and allows us to see warm objects like stellar and planetary nurseries significantly better."

The coating is applied in multiple layers in order to accurately control the thickness of the various materials. Each layer is extremely thin, with the silver layer only about 0.1 microns thick or about 1/200 the thickness of a human hair.

A similar coating process is commonly used for architectural glass to reduce air-conditioning costs and produce an aesthetic reflection and color to glass on buildings, but this is the first time it has been applied to a large astronomical telescope mirror.

Each of the Gemini mirrors -- in Chile and Hawaii -- are 26.6 feet (8.1-meters) wide and weigh 24 tons. The coating was completed May 31 and the mirror is back in the telescope.

-- SPACE.com Staff

Credit: Kirk Pu'uohau Pummill, Gemini