ROYAL ASTRONOMICAL SOCIETY / SCIENCE PHOTO LIBRARY ROYAL ASTRONOMICAL SOCIETY / SCIENCE PHOTO LIBRARY
Telescope clock. Pendulums and gear system of a driving clock used for a telescope. This mechanism, similar to that used in a clock or watch, is used to ensure that telescopes are moved at a steady rate across the sky to follow a celestial object as the Earth rotates. The telescope, on an equatorial mount, is turned to rotate on its polar axis. This rotation allows long exposure times and greater detail to be obtained. Photographed at the Sydney Observatory, Sydney, Australia. This observatory was established in 1858, and devices like this were in use here in the 1880s in devices such as the star camera.
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