Parting Shot: Resurfacing the Mirror

6:32 a.m. Thursday

Basement of Gemini Observatory,
Mauna Kea summit, Hawaii Island

Photo Courtesy of Gemini Observatory

>>Technicians from Hawaii and Chile combine forces about every four years to resurface this 24-ton, 27-foot mirror from the Gemini North telescope. Hawaii engineers were in Chile last month to help resurface an identical telescope there, but this picture was taken during the last Hawaii resurfacing in 2008. The job takes up to 10 days and includes lifting the mirror from its fittings with cranes and resting it on a wash cart in the observatory’s basement. In this picture, engineers lay on platforms suspended over the mirror to remove the four-layer surface, which includes a layer of highly reflective silver. The new coating – about 1/1,000th the thickness of a human hair – is layered on using a magnetron in a vacuum chamber.