30 • Astronomy Basics
Like the Sun, the stars also appear to move across the sky. This motion is
caused by the Earth’s rotation. For observers in the northern hemisphere, all
stars appear to move around the north celestial pole. For observers in the
southern hemisphere, all stars appear to move around the south celestial pole.
This means that over a 24-hour period, any given star will scribe out a complete
circle around its respective celestial pole. The farther you move away from the
celestial pole, the larger this circle becomes and is largest at the celestial
equator. Stars near the celestial equator rise in the east and set in the west.
However, stars near the celestial poles are always above the horizon. They are
said to be circumpolar because they don’t rise and set. You will never see the
stars complete one circle because the sunlight during the day washes out the
starlight. However, part of this circular motion of stars in this region of the sky
can be seen by setting up a camera on a tripod and opening the shutter for a
couple of hours. The processed film will reveal circular arcs that are centered
on the pole. This information will be useful for certain methods of polar align-
ment.
Figure 5-2
All stars appear to rotate around the celestial poles. However, the appearance of this
motion varies depending on where you are looking in the sky. Near the north celestial
pole the stars scribe out recognizable circles centered on the pole (1). Stars near the
celestial equator also follow circular paths around the pole. But, the complete path is
interrupted by the horizon. These appear to rise in the east and set in the west (2).
Looking toward the opposite pole, stars curve or arc in the opposite direction scribing a
circle around the opposite pole (3).
Motion of the Stars
