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A means of turning the mounting of a telescope to counteract the motion of a celestial object across the sky as the Earth rotates; also called a clock drive. An electric or a clockwork motor is used to drive the telescope or, in older telescopes, a slowly falling weight. Electronics can control the rate of the motor and provide speed corrections to compensate for mechanical errors in the telescope mounting and the effects of atmospheric refraction.

Subjects: Astronomy and Astrophysics.

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