Specifications

Making the telescope's axis of rotation parallel to the Earth's
Polar aligning your G-8/G-11 or CI700Mount
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. A polar axis finder is offered as an optional
accessory. 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. The polar axis is the axis
around which the telescope rotates when moved in right ascension. This axis points in the same
direction even when the telescope moves in right ascension.
Polar alignment is the process by which the telescope's axis of rotation (called the polar axis) is
made parallel with the Earth's axis of rotation. Once aligned, a telescope with a _9{)II system will
track the stars as they move across the sky. The result is that objects observed through the
telescope appear stationary. They will not drift out of the field of view because the motors and
gears exactly compensate for the motion 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 R.A. axis. There are several methods of
polar alignment, all of which work on a similar principal, but perform somewhat differently. Each
method will be 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 astro-photography.
Where are the Poles?
In each hemisphere, there is a point in the sky around which all the other stars appear to rotate.
These points are called the celestial poles and are named for the hemisphere in which they
reside. For example, in the Northern Hemisphere all stars move around the North Celestial Pole.
When a telescope's polar axis is pointed at the celestial pole, it is parallel to the Earth's rotational
axis. The North Celestial Pole is the point in the Northern Hemisphere around which all stars
appear to rotate. The counterpart in the Southern Hemisphere is referred to as the South
Celestial Pole.
Many of the methods of polar alignment require that you know how to find the celestial pole by
identifying stars in the area. For those in the Northern Hemisphere, finding the celestial pole is not
too difficult. Fortunately, we have a naked eye star less than a degree away. This star, Polaris, is
the end star in the handle of the Little Dipper. Since the Little Dipper (technically called Ursa
Minor) is not one of the brightest constellations in the sky, it may be difficult to locate from urban
areas. If this is the case, use the two end stars in the bowl of the Big Dipper (the pointer stars).
Draw an imaginary line (away from the "pan") through them toward the Little Dipper. They point
almost directly to Polaris. Since the position of the Big Dipper rotates throughout the night as well
as during the year it may be difficult to locate, or even perhaps be below the horizon .
Observers in the Southern Hemisphere are not as fortunate as those in the Northern Hemisphere.
The stars around the south celestial pole are not nearly as bright as those around the North
Celestial Pole. The closest star that is relatively bright is Sigma Octantis. This star is just within
the naked eye limit (magnitude E.5) and lies about 59 arc minutes from the pole. For more
information about stars around the south celestial pole, please consult a star atlas.
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