Motion Of The Stars - Celestron Ultima 11 Instruction Manual

The daily motion of the Sun across the sky is familiar to even the most casual observer. This daily trek is
not the Sun moving as early astronomers thought, but the result of the Earth's rotation. The Earth's rotation
also causes the stars to do the same, scribing out a large circle as the Earth completes one rotation. The size
of the circular path a star follows depends on where it is in the sky. Stars near the celestial equator form the
largest circles rising in the East and setting in the West. Moving toward the north celestial pole, the point
around which the stars in the northern hemisphere appear to rotate, these circles become smaller. Stars in
the mid-celestial latitudes rise in the Northeast and set in the Northwest. Stars at high celestial latitudes are
always above the horizon, and are said to be circumpolar because they never rise and never 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 semicircles that
revolve around the pole. (This description of stellar motions also applies to the southern hemisphere,
except all stars south of the celestial equator move around the south celestial pole.)
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

Figure 4-2
1
Ultima 9 / and Ultima 11 Manual
4
31