In astronomy

Astronomy

Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...

 a Clock drive is a regulatory mechanism used to move an equatorial mount

Equatorial mount

An equatorial mount is a mount for instruments that follows the rotation of the sky by having one rotational axis parallel to the Earth's axis of rotation. This type of mount is used for astronomical telescopes and cameras...

ed telescope

Telescope

A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...

 along one axis to keep the telescope in exact sync with the apparent motion of the celestial sky (diurnal motion

Diurnal motion

Diurnal motion is an astronomical term referring to the apparent daily motion of stars around the Earth, or more precisely around the two celestial poles. It is caused by the Earth's rotation on its axis, so every star apparently moves on a circle, that is called the diurnal circle. The time for...

). They achieve this by rotation the axis parallel to the Earths polar axis (called the right ascension

Right ascension

Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...

 axis) in the opposite direction to the Earths rotation one revolution every 23 hours and 56 minutes (called sidereal day

Sidereal time

Sidereal time is a time-keeping system astronomers use to keep track of the direction to point their telescopes to view a given star in the night sky...

), thereby canceling that motion. The mechanism itself used to be clockwork

Clockwork

A clockwork is the inner workings of either a mechanical clock or a device that operates in a similar fashion. Specifically, the term refers to a mechanical device utilizing a complex series of gears....

 but now days is usually electrically driven. Clock drives can be light and portable for smaller telescopes or can be exceedingly heavy and complex for larger ones such as the 60 inch telescope at the Mount Wilson Observatory

Mount Wilson Observatory

The Mount Wilson Observatory is an astronomical observatory in Los Angeles County, California, United States. The MWO is located on Mount Wilson, a 5,715 foot peak in the San Gabriel Mountains near Pasadena, northeast of Los Angeles...

. Clock-driven equatorial platform

Equatorial platform

An equatorial platform or equatorial table is an equatorial telescope mount in the form of a specially designed platform that allows any device sitting on it to track astronomical objects in the sky on an equatorial axis. They are used to give equatorial tracking to any device sitting on them, from...

s are sometimes used non-tracking type mounts, such as altazimuth mount

Altazimuth mount

An altazimuth or alt-azimuth mount is a simple two-axis mount for supporting and rotating an instrument about two mutually perpendicular axes; one vertical and the other horizontal. Rotation about the vertical axis varies the azimuth of the pointing direction of the instrument...

s.