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Starts seen near the north celestial
pole
Starts seen near the celestial
equator
Starts seen looking in the opposite
direction of the north 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).
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The easiest way to polar align a telescope is with a latitude scale. Unlike other methods that require you to find the
celestial pole by identifying certain stars near it, this method works off of a known constant to determine how high the
polar axis should be pointed. The AstroMaster CG-2 mount can be adjusted from about 20 to 60 degrees (see figure 4-3).
The constant, mentioned above, is a relationship between your latitude and the angular distance the celestial pole is
above the northern (or southern) horizon. The angular distance from the northern horizon to the north celestial pole is
always equal to your latitude. To illustrate this, imagine that you are standing on the north pole, latitude +90°. The
north celestial pole, which has a declination of +90°, would be directly overhead (i.e., 90 above the horizon). Now,
let's say that you move one degree south — your latitude is now +89° and the celestial pole is no longer directly
overhead. It has moved one degree closer toward the northern horizon. This means the pole is now 89° above the
northern horizon. If you move one degree further south, the same thing happens again. You would have to travel 70
miles north or south to change your latitude by one degree. As you can see from this example, the distance from the
northern horizon to the celestial pole is always equal to your latitude.
If you are observing from Los Angeles, which has a latitude of 34°, then the celestial pole is 34° above the northern
horizon. All a latitude scale does then is to point the polar axis of the telescope at the right elevation above the
northern (or southern) horizon. To align your telescope:
1.
Make sure the polar axis of the mount is pointing due north. Use a landmark that you know faces north.
2.
Level the tripod. Leveling the tripod is only necessary if using this method of polar alignment.
3.
Adjust the mount in altitude until the latitude indicator points to your latitude. Moving the mount affects the angle
the polar axis is pointing. For specific information on adjusting the equatorial mount, please see the section
"Adjusting the Mount."
This method can be done in daylight, thus eliminating the need to fumble around in the dark. Although this method
does NOT put you directly on the pole, it will limit the number of corrections you will make when tracking an object.
Figure 4-2
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Figure 4-3
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