Polar alignment is the method of aligning the rotational axis of an telescope mount of the equatorial type such as a GEM mount, to be parallel with that of the Earth's rotation. There are many ways to achieve polar alignment, and the methods, including advantages and disadvantages are discussed below.


[top]Rough Polar Alignment Methods

[top]Using a Compass to Find Celestial Pole

For the Northern Hemisphere you are trying to point roughly North or N on a compass. However the more accurate method is to calculate magnetic north for your location .

For the Southern Hemisphere you are trying to point roughly South or S on a compass. However the more accurate method is to calculate magnetic south.


Compass below demonstrating Sydney True South for Telescope Southern Polar Alignment.
The line is set for 165 degrees which is True South. The white arrow is pointing to Magnetic South.



Setting Altitude of Mount





Setting Azimuth

[top]Other methods to Align to Latitude

[top]Digital Angle Gauge


Digital angle gauges are more accurate than the angle settings on a mount, the mount angles were set at 34.5 degrees however the digital gauge read at 29.9 degrees an error of about 4.5 degrees.

[top]Angle Calculation Method with Laser


I set up my wedge or GE mount once for my home and leave it set. If I move it any substantial distance (which is rare) I adjust azimuth with the tripod legs.
You can set it accurately with a laser pointer, tape measure and a hard floor.

Take the mount off the tripod and sit it on the floor a known distance from a wall. Say 10ft or 3m.
Sit the laser pointer on top of the mount and measure the distance to the floor (say 4").
Get out the calculator and find the Tangent of your latitude.
If it's 35 degrees, enter 35 and hit the "Tan" button.
Tan of 35 degrees is 0.70.
Multiply this number by the distance from the wall to get the height (10 * 0.70 = 7ft).
Add on the height of the mount (4" in our example) to get the total height (7ft 4").
Adjust the mount to get the laser dot at that height and lock it.
If your measurements are within 1/8", the latitude will be within a few minutes of arc.
-Steve

[top]Polar Alignment with a Polar Scope

Using a Polar Scope



Image from KeithBC below demonstrating the polar scope view.

[top]Southern Hemisphere Polar Alignment

[top]More Accurate Polar Alignment Methods


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