Celestar Manual
Astronomy Basics
31
POLAR ALIGNMENT
In order for the telescope to track the stars, you must meet two criteria. First, you need a drive motor that
moves at the same rate as the stars. The Celestron telescope comes standard with a built-in drive motor
designed specifically for this purpose. The second thing you need is to set the telescope's axis of rotation
so that it tracks in the right direction. Since the motion of the stars across the sky is caused by the Earth's
rotation about its axis, the telescope's axis must be made parallel to the Earth's.
Polar alignment is the process by which the telescope's axis of rotation (called the polar axis) is aligned
(made parallel) with the Earth's axis of rotation. Once aligned, a telescope with a clock drive will track the
stars as they move across the sky. The result is that objects observed through the telescope appear
stationary (i.e., they will not drift out of the field of view). If not using the clock drive, all objects in the
sky (day or night) will slowly drift out of the field. This motion is caused by the Earth's rotation. Even if
you are not using the clock drive, polar alignment is still desirable since it will reduce the number of
corrections needed to follow an object and limit all corrections to one axis (R.A.). There are several
methods of polar alignment, all work on a similar principle, but performed somewhat differently. Each
method is considered separately, beginning with the easier methods and working to the more difficult.
Although there are several methods mentioned here, you will never use all of them during one particular
observing session. Instead, you may use only one if it is a casual observing session. Or, you may use two
methods; one for rough alignment followed by a more accurate method if you plan on doing
astrophotography.
Definition:
The polar axis is the axis around which the telescope rotates when moved in right
ascension. This axis points the same direction even when the telescope moves in right
ascension and declination.
Figure 4-3
