EQUATORIAL MOUNT

An 'equatorial mount' is a mount used for moving a telescope or camera along two perpendicular axes of motion known as ''right ascension'' and ''declination''. Equatorial mounts are often equipped with a motor drive for automatic tracking of objects across the night sky. They may also be equipped with setting circles to allow for the location of objects by their celestial coordinates.
The advantage of an equatorial mount lies in its ability to track an object moving across the sky using constant speed movement around only one axis, unlike an altazimuth mount, which requires variable speed motion around both axes to track the diurnal motion. Also, for astrophotography, the image does not rotate in the focal plane, as occurs with altazimuth mounts when they are guided to track the target's motion, unless a rotating erector prism is installed (or other field-derotator).
The telescope mount's axis of right ascension should be pointed directly towards whichever celestial pole is above the horizon. This polar alignment is dependent on the location of the observer and corresponds with the latitude of the observer's location. Once aligned, the right ascension axis is parallel to the Earth's axis of rotation and celestial objects can be tracked without actuating the declination axis.

Contents

English mount

German mount

English fork

Open fork

See also

English mount

The ''English mount'' system is like a big '+'-sign.
The ''right ascension'' axis is supported at both ends, and the ''declination'' axis is attached to it at approximately mid point.
The telescope is placed on one end of the declination axis, and a suitable counterweight on other end of it.

German mount

In the 'German mount' the primary structure is a 'T'-shape, where the lower bar is the ''right ascension'' axis,
and the upper bar is the ''declination'' axis. The right ascension axis has bearings below the T-joint, that is, it is not supported above the declination axis.
The telescope is placed on one end of the declination axis, and suitable counterweight on other end of it.
This is most common type of telescope mounts, and many amateur telescopes from 60 mm (2.4") refractors to 14" Schmidt-Cassegrain telescopes are mounted on this mount.

English fork

In 'English Fork' there is a frame that has ''right ascension'' axis bearings at the top and the bottom ends, and the ''declination'' axis is at its approximate midpoint.
The telescope is fitted entirely inside the fork (or not, as is the case with Mt. Wilson 2.5 m reflector) and there are no counterweights like ''german mount'' has.
Original ''english fork'' has the disadvantage of being blocked by the frame from pointing to near north (or south) pole of the sky.
For example the Hale telescope is an ''english fork'' even though the north end has been changed into huge horse shoe so that it can point to north pole.

Open fork

Most modern mass-produced catadioptric reflecting telescopes (200 mm or larger diameter) tend to be of this type. The mount resembles an Altazimuth mount, but with the azimuth axis is tilted and lined up to match earth rotation axis with a piece of hardware usually called a "wedge."
Many mid-size professional telescopes also have ''equatorial forks'', these are usually in range of 0.5-2.0 meter diameter.

See also

★ Equatorial room

★ Telescope

★ Telescope mount

★ Altazimuth mount