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Declination Drift
This method of polar alignment allows you to get the most accurate alignment on the celestial pole and is required if you
want to do long exposure deep-sky astrophotography through the telescope. The declination drift method requires that
you monitor the drift of selected stars. The drift of each star tells you how far away the polar axis is pointing from the true
celestial pole and in what direction. Although declination drift is simple and straight-forward, it requires a great deal of
time and patience to complete when first attempted. The declination drift method should be done after any one of the
previously mentioned methods has been completed.
To perform the declination drift method you need to choose two bright stars. One should be near the eastern horizon and
one due south near the meridian. Both stars should be near the celestial equator (i.e., 0° declination). You will monitor
the drift of each star one at a time and in declination only. While monitoring a star on the meridian, any misalignment in
the east-west direction is revealed. While monitoring a star near the east/west horizon, any misalignment in the north-
south direction is revealed. As for hardware, you will need an illuminated reticle ocular to help you recognize any drift.
For very close alignment, a Barlow lens is also recommended since it increases the magnification and reveals any drift
faster.
When looking due south, insert the diagonal so the eyepiece points straight up. Insert the cross hair ocular and align the
cross hairs so that one is parallel to the declination axis and the other is parallel to the right ascension axis. Move your
telescope manually in R.A. and DEC to check parallelism.
First, choose your star near where the celestial equator and the meridian meet. The star should be approximately within
1/2 an hour of the meridian and within five degrees of the celestial equator. Center the star in the field of your telescope
and monitor the drift in declination.
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If the star drifts south, the polar axis is too far east.
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If the star drifts north, the polar axis is too far west.
Make the appropriate adjustments to the polar axis to eliminate any drift. Once you have eliminated most of the drift,
move to the star near the eastern horizon. The star should be 20 degrees above the horizon and within five degrees of the
celestial equator.
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If the star drifts south, the polar axis is too low.
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If the star drifts north, the polar axis is too high.
Again, make the appropriate adjustments to the polar axis to eliminate any drift. Unfortunately, the latter adjustments
interact with the prior adjustments ever so slightly. So, repeat the process again to improve the accuracy checking both
axes for minimal drift. Once the drift has been eliminated, the telescope is very accurately aligned. You can now do
prime focus deep-sky astrophotography for long periods.
NOTE: If the eastern horizon is blocked, you may choose a star near the western horizon, but you must reverse the polar
high/low error directions. Also, if using this method in the southern hemisphere, the direction of drift is reversed for both
R.A. and DEC.
The 7x50mm Finder
Another general method of polar alignment is by using the Polaris finderscope. Built into the Polaris finder is a reticle
with a single cross hair and two circles which will be used for polar alignment. The inner circle is approximately 4/5 of a
degree in radius, roughly the distance between Polaris and the celestial pole. In order to use the 7x50 Polaris finder, you
