Telescope mountings

The most important thing about a telescope mounting used for astronomy is that it should be firm and free from vibrations.

Astronomical telescopes are usually mounted in one of two ways:
(a) altazimuth – one axis of the mounting vertical and the other horizontal
(b) equatorial – one axis of the mounting in line with the axis of the Earth and the other at right angles to this

The two type of mounting have advantages and disadvantages:
(a) altazimuth
(i) advantages – a relatively cheap and simple type of mounting
(ii) disadvantages – The telescope must be moved about both the azimuth axis (left and right) as well as the altitude axis (up and down) to follow a star across the sky as the Earth rotates.
(b) equatorial
(i) advantages – because one axis (the polar axis) of the telescope is in line with the Earth's axis the telescope has only to move about this axis to follow a star across the sky. The declination of the telescope is fixed and then can remain unaltered if the telescope is set up properly.
(ii) A more costly and sophisticated mounting but well worth it for the advantage in the ease with which it can follow a star

Each mounting has two axes:
Altazimuth mounting
(a) altitude axis (for moving the telescope up and down)
(b) azimuth axis (for moving the telescope side to side)
(You can see where the name alt-azimuth comes from)
Equatorial
(a) polar axis (for moving the telescope around the polar axis of the Earth
(b) declination axis (for moving the telescope at right angles to the polar axis

The next diagram shows how both types of mounting allow the telescope to follow the stars.




The next diagrams show the angle at which the polar axis of your telescope must be set. To make it simpler the angle of tilt of the Earth has been ignored.