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Polar alignment is necessary if you need the telescope to track the night sky. For normal observing with an equatorially mounted telescope, only rough polar alignment is necessary. When polar aligned, the RA motor on the equatorial mount will move the telescope in motion with the stars, nebulae and galaxies etc. so that they remain stationary relative to the eyepiece. Also, star positions can be located using the setting circles on the telescope equatorial mount.
Celestron have an excellent article on polar alignment in the Northern Hemisphere so I will not repeat the instructions here. The situation is somewhat different for the southern hemisphere and I have found the following procedure helpful
Polar Alignment in the Southern Hemisphere
1. Setup your
tripod with the equatorial mount but not with the telescope
attached.
2. Put the equatorial mount in it's normal upright position
pointing south.
3. Make sure the mount is firmly seated on the tripod and the
tripod is stable.
4. Set the latitude scale on the mount to your current latitude
5. Use a compass to point the equatorial mount true south, not
magnetic south. Be as accurate as possible.
6. Your mount should be roughly polar aligned
7.The mount is currently pointing due south but most observers
will want to view the northern sky as this is where most of the
interesting objects are located, including the planets, moon and
Orion Nebula.
8. Rotate the mount 90 degrees on its RA axis and 180 degrees on
its DEC axis so it is pointing north.
9. Attach the Telescope to the mount
Fine Adjustment:
1. Use the drift method to finely adjust the tracking on your
mount.
2. Locate a bright star in the northern sky, close to the
celestial equator and meridian and turn on your RA tracking motor
3. A cross hair eyepiece on your finder or focuser is required.
Align the crosshairs so they point parallel to the RA and DEC
axes of your telescope.
3. Watch how the star drifts through the eyepiece.
If it remains centered then the polar alignment is correct.
If it drifts north then the polar axis is too far east, move the
mount slightly west with the azimuth adjustments and try again.
If it drifts south then the polar axis is too far west,move the
mount slightly east with the azimuth adjustments and try again.
Your mount
should now be accurately polar aligned.
You can also check the latitude adjustment using the following
procedure:
1. Point the telescope towards the eastern horizon
2. Locate a bright star and turn the tracking motor on.
3. Observe how the star drifts through the eyepiece
If it remains centered then the polar alignment is correct.
If it drifts north then the polar axis is too low, increase the
latitude scale on your mount
If it drifts south then the polar axis is too high, decrease the
latitude scale on your mount
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