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Figure 4-6
Aligning the equatorial mount to the polar axis of the Earth
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Polar alignment to the South Celestial Pole (SCP) is a little more challenging due to the fact that there is no very
bright star close to it like Polaris is in the NCP. There are various ways to polar align your telescope and for casual
observing the methods below are adequate and will get you reasonably close to the SCP.
Polar Alignment with the Latitude Scale
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 constant, mentioned above, is a relationship between your latitude and
the angular distance the celestial pole is above the southern horizon. The
angular distance from the southern horizon to the south celestial pole is
always equal to your latitude. To illustrate this, imagine that you are
standing on the south pole, latitude -90°. The south 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 north — your latitude is
now -89° and the celestial pole is no longer directly overhead. It has moved
one degree closer toward the southern horizon. This means the pole is now
89° above the southern horizon. If you move one degree further north, 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 southern horizon to the celestial pole is always equal
to your latitude.
Figure 4-7
If you are observing from Sydney, which has a latitude of -34°, then the celestial pole is 34° above the southern
horizon. All a latitude scale does then is to point the polar axis of the telescope at the right elevation above the
southern horizon. To align your telescope:
1. Make sure the polar axis of the mount is pointing due south. Use a landmark that you know faces south.
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” in your telescope manual.
4. If the above is done correctly, you should be able to observe near the pole through the finderscope and a low
power eyepiece.
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.
