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Motion of the Stars
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 alignment.
Figure 6-2 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).
