Clock drive

In astronomy, a clock drive (also known as a sidereal drive or field rotator) is a motor-controlled mechanism used to move an equatorial mounted telescope along one axis to keep the aim in exact sync with the apparent motion of the fixed stars on the celestial sphere.

[2] This allows the telescope to stay fixed on a certain point in the sky without having to be constantly re-aimed due to the Earth's rotation.

[5] The original inventor of the clock drive is unknown, being an idea that was tried in several ways throughout history.

[7] Different types of equatorial clock-driven telescopes were built or proposed in the 17th and 18th century including English astronomer Robert Hooke's 1674 paper proposing their use in precision measurement,[8] a clock-driven aerial telescope objective lens constructed in 1685 by Italian-French astronomer Giovanni Domenico Cassini fitted with setting circles,[9] and one supposedly built by English clockmaker and inventor George Graham early 18th century.

[14] Over time the falling weights and pendulums were replaced by an electric motor.