An equatorial mount is a type of astronomical telescope mount that has one of its rotational axes, called the right ascension axis, arranged to be parallel with the rotational axis of the Earth.  There is a second axis perpendicular to the right ascension axis called the declination axis.

The main advantage of this arrangement is that by ensuring that the right ascension axis is correctly aligned to be parallel to the Earth's axis (polar alignment) and driving it at the same rate as the rotation of the Earth (sidereal rate), it is possible to track objects in the night sky accurately with no other motion needed.   Equatorial mounts are usually equipped with setting circles to enable them to be positioned accurately on an object by using its celestial co-ordinates.  The setting circle on the right ascension axis is divided into hours, minutes and seconds and the setting circle on the declination axis is divided into degrees minutes and seconds.

There are several popular configurations of the equatorial mount and the common ones are listed below.

German equatorial mount or GEM.

This is the most popular type of equatorial mount and the type that is probably most familiar to amateur astronomers and has a T shape with the lower axis being the right ascension axis, and the upper the declination.  GEMs can be very portable and quickly set up.

Fork mount or open fork mount.

This is also a popular type of equatorial mount and is the type most commonly used with catadioptric telescopes as their short tube length is suitable for this type of mount.  In the fork mount, the base of the fork is mounted and rotates on the right ascension axis with the tube mounted within the fork itself with this forming the declination axis.  Fork mounts are also used as alt-azimuth mounts the difference between the two types being the polar angle provided by a fixed or adjustable wedge which is only present in the equatorial version.

Horseshoe or split ring mount.

English mount

Cross axis mount