Celestar Manual
Astronomy Basics
32
Finding the Pole
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 4-5). The position of the Big Dipper changes during the
year and throughout the course of the night (see Figure 4-4). 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 4-5).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. For more information about stars
around the south celestial pole, please consult a star atlas.
Definition: 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.
Figure 4-5
The two stars in the front of the bowl of the Big Dipper point to Polaris which is less
than one degree from the true (north) celestial pole. Cassiopeia, the “W” shaped
constellation, is on the opposite side of the pole from the Big Dipper. The North
Celestial Pole (N.C.P.) is marked by the “+” sign.
