Polar Alignment


Polar alignment is the process by which the telescope's axis of rotation (called the polar axis) is aligned (made parallel) with the Earth's axis of rotation. Once aligned, a telescope with a clock drive will track the stars as they move across the sky. The result is that objects observed through the telescope appear stationary (i.e., they will not drift out of the field of view).


In each hemisphere, there is a point in the sky around which all the other stars appear to rotate, called celestial poles. For example, in the northern hemisphere all stars move around the north celestial pole. When the telescope's polar axis is pointed at the celestial pole, it is parallel to the Earth's rotational axis. For those in the northern hemisphere, finding the celestial pole is not too difficult. Fortunately, we have a visible star less than a degree away. This star, Polaris, is the end star in the handle of the Little Dipper (Ursa Minor).

Set the telescope up so that the polar axis (fork arm) is pointing north.

Check the alignment of the finderscope by placing a low power eyepiece in the telescope. Point the telescope at a bright star or the moon and center it in the eyepiece. If the star does not also appear near the center of the finderscope (and Telrad), adjust the finderscopes until the star is in the crosshairs.

Loosen the declination lock and move the telescope so that the declination setting circle reads 90º. When this is done the tube is parallel to the polar axis.

Adjust the mount in altitude and azimuth until Polaris is visible in the finder. Once visible in the finder, raise the telescopes wheels off the ground so the tripod cannot roll.

Center Polaris in the finderscope using the altitude and azimuth adjustment knobs. Do not move the tube itself.

To find the true celestial pole, adjust the mount so that Polaris moves about 1/3 the way from the center to the edge of the finderscope field, in the direction of the star Kochab, at the cup end of the Little Dipper (see illustration).

Double-check that the declination circle still reads 90°. If it does, you are properly polar aligned. If it doesn’t read 90º go back to step 3.


Using the Setting Circles

In order to set the Right Ascension (RA) circle, you must first choose a bright star that you know that is near the object you want to observe.

By moving the tube, center the bright star in the finderscope and the eyepiece. Remember not to move the telescope mount after the telescope has been polar aligned.

If you haven’t already done so, start the clock drive so that the telescope tracks the star.

Look up the coordinates of the bright star.


Rotate the RA circle until the proper coordinates line up with the R.A. indicator. Make sure you use the inner set of numbers on the RA circle. The R.A. setting circle has a marker every five minutes with each hour labeled.

Check the coordinates of the declination circle. If you did your polar alignment correctly, the declination circle should be set to the coordinates of the bright star. If the declination circle is off by more than 2 degrees, go back and repeat step 3 of the Polar Alignment procedure. No not try to adjust the declination circle.

Loosen the locks and move the telescope tube one axis at a time to the Right Ascension and declination of the first object you want to observe. Do not move the RA circle, only the telescope tube. You should plan your observing session well in advance and have the coordinates written in your notebook.

Look in the low power eyepiece for the object. If the object is not visible in the eyepiece, look for the object in the finderscope. If the object is visible in the finder, center the object in the crosshairs of the finder then look for it in the eyepiece. If you still can’t find the object, go back and repeat step 2.

Once the object has been found and sketched. Update the RA circle to the coordinates of the centered object and repeat steps 2 thru 8 to find your next object.