SPUTNIK / SCIENCE PHOTO LIBRARY SPUTNIK / SCIENCE PHOTO LIBRARY
Atomic clock. A scientist checking an atomic clock at a radio telescope observatory. There are two clocks shown here, the one on the left (marked 'zvyezdnoye vryemya') gives sidereal time, the one on the right (marked 'solnyechnoye vryemya') gives solar time. Atomic clocks are used in astronomy for very precise synchronisation of observations made from different sites. Photographed at the Mount Aragats Observatory in Armenia in 1987.
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