26
Figure 4-4
Remember, while Polar aligning, DO NOT move the telescope in R.A. or DEC. You do not want to
move the telescope itself, but the polar axis. The telescope is used simply to see where the polar axis is
pointing.
Like the previous method, this gets you close to the pole but not directly on it. The following methods help
improve your accuracy for more serious observations and photography.
F
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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 the telescope's polar axis is pointed
at the celestial pole, it is parallel to the Earth's rotational axis.
Many 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 through them toward the Little Dipper. They
point to Polaris (see Figure 4-6). The position of the Big Dipper (Ursa
Major) changes during the year and throughout the course of the night (see
Figure 4-5). When the Big Dipper is low in the sky (i.e., near the
horizon), it may be difficult to locate. During these times, look for
Cassiopeia (see Figure 4-6). 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. The
closest star that is relatively bright is Sigma Octantis. This star is just
within naked eye limit (magnitude 5.5) and lies about 59 arc minutes from
the pole.
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.
Definition
Figure 4-5
The position of the Big
Dipper changes throughout
the year and the night.
Spring
Polaris
(North Star) Winter
Summer
Fall
