JOHN K. DAVIES / SCIENCE PHOTO LIBRARY JOHN K. DAVIES / SCIENCE PHOTO LIBRARY
South African Astronomical Observatory (SAAO) telescope dome with star trails. Star trails are formed on long exposure photographs by the apparent movement of the stars across the sky caused by the Earth's rotation. The telescope building is enclosed by silvered blinds. These reduce the amount of heat taken in by the building during the day, which speeds temperature equalisation before observations begin at night. Mixing warm and cool air causes turbulence that impairs the viewing conditions. This observatory is based at Sutherland, South Africa. This site has an altitude of 1800 metres, which places it above much of the cloud.
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