Polar Alignment

If your telescope uses an equatorial mount, you will have to align the mount with the north star, Polaris, in order for the telescope to track properly. For basic visual observing, polar alignment is not particularly critical and is easy to do. For more precise alignment, such as when using a computerized telescope, there are a few extra steps. Only for deep-sky photography is a very critical polar alignment necessary. The steps below are divided into three sections based on the type of alignment necessary.

Basic Polar Alignment

This is the only step necessary for basic viewing with an equatorial mount. It is also the first step in getting a more accurate alignment.

• If possible, use a bubble level to level the tripod

• If your telescope has a latitude scale, set it to your latitude as shown below

Above: Setting the latitude scale on an equatorial mount, in this case to 32°

Note: Don't know your latitude? No problem, click here.

• Sight over the top of the right ascension axis and adjust the mount left or right to aim toward Polaris

Above: The two stars in the end of the Big Dipper's handle always point toward Polaris, the North Star. This chart shows the position of the Big Dipper and Cassiopeia in the evening in early summer. As the seasons progress these constellations will rotate from month to month in a counterclockwise direction around Polaris.

Tip: If you have leveled the tripod and set the latitude scale, you should only have to move the mount left or right to align with the pole. The up and down adjustment should be set already.

For visual work, this will be sufficient. If using a computerized equatorial mount or taking long-exposure astrophotos, continue to the next step.

Improved Polar Alignment

The next step is to fine tune the polar alignment. Polaris is conveniently located near the north celestial pole, but does not exactly coincide with it. There are two common methods for improving the polar alignment: a polar alignment scope, and computerized polar alignment. Many computerized equatorial mounts (including fork-mounted telescopes on wedges) have a polar alignment routine built in to their software to provide a more accurate alignment. For non-computerized telescopes, a polar scope is the best option.

Polar Alignment Scope

A polar alignment scope is a very small finderscope which gives a slightly magnified view of the area around Polaris. The scope has an etched reticle (usually illuminated) that shows the offset from Polaris to true celestial north. Once the polar scope is properly calibrated, the mount is simply adjusted to put Polaris in the proper location on the reticle and a more accurate polar alignment is achieved.

Above: View through a typical polar alignment scope

• Begin by setting the polar scope to the proper orientation

For polar scopes with the Big Dipper and Cassiopeia drawn on the reticle, this is simply a matter of rotating the polar scope until the reticle matches the orientation of these constellations in the sky. For polar scopes with only the offset of Polaris shown, this is also relatively simple. See the diagram below.

Above: How to orient a simple polar alignment scope. Rotate the reticle until so the angle between the center of the crosshairs and the small outer circle corresponds to the angle between Polaris and Beta Ursae Minoris (the brightest star in the bucket of the Little Dipper).

• Once the polar scope is oriented, simply adjust the altitude and azimuth adjustments on the mount to place Polaris in the proper location in the reticle

Computerized Polar Alignment

The exact procedure used with each telescope will be slightly different. This section gives a basic overview of the procedure. For step-by-step instructions on computerized polar alignment of a specific telescope, please visit the section on Aligning a Computerized Telescope.

This alignment will suffice for finding objects with a computerized telescope, and for shorter exposure or wide-field photography. For the highest precision for long-exposure imaging, see the next section of drift polar alignment.

Declination Drift Alignment

Once you have read the directions below, you may wish to print out the Drift Alignment Quick Reference to have with you in the field. The drift method of polar alignment requires the use of an illuminated crosshair eyepiece. A simple double-crosshair (shown below) works perfectly, although a fancier eyepiece such a Celestron's Micro Guide eyepiece will work fine as well.

Note: These instructions apply to telescopes which use diagonals such as SCTs, RCs, and refractors. Newtonian-style telescopes will need to reverse certain directions where noted.

Above: The view through a typical illuminated crosshair eyepiece.

Azimuth Adjustment

• The drift alignment requires that you let the telescope track on two different stars in specific locations in the sky. Watching how the stars drift relative to the reticle in the crosshair eyepiece tells you how far the mount is offset from true celestial north and in which direction.

• Pick a star near the meridian, just north of the celestial equator (due south, between about 60°-70° above the horizon from the U.S.). Select a star that is reasonably bright but not too bright (about magnitude 3-4). Be sure that no other similar stars are in the field of view, as you do not want to get confused as to which star is which.

• Aim the telescope to this star. Rotate the diagonal until the eyepiece is oriented so that you are standing on the north side of the telescope when looking into the eyepiece. This step is not absolutely necessary but will make the following procedure easier.

• The crosshairs of the eyepiece must be aligned with the north-south and east-west directions. Center the star in the eyepiece. Use the mount's hand-controller to move the star east and west (roughly left and right) in the eyepiece. You should see that the star's motion is not perfectly parallel to the horizontal lines in the eyepiece. Rotate the eyepiece and check the east-west motion again. Repeat until the crosshairs are properly aligned.

Above: Rotate the eyepiece so that the crosshairs are parallel to the east-west motion of the star in the telescope.

• Once the crosshairs are oriented, place the star on one of the lines east-west (approximately horizontal) lines. In other words, the star image should be bisected by one of the horizontal lines as shown below. Do not place the star between the lines, as it will not provide enough accuracy for the following steps.

Above: Place star on east-west line.

• Let the telescope track for a minute or so. You will see the star begin to drift off of the line. It will drift either north (above the line) or south (below the line). Ignore any east-west (left-right) drift.

Newtonian telescope users must reverse the following directions

• If the star drifts up, use the mount's azimuth adjustment knobs to move the mount so that the star appears to move right in the field of view.

• If the star drifts down, use the mount's azimuth adjustment knobs to move the mount so that the star appears to move left in the field of view.

• Use the hand-controller to move the star back onto the horizontal line.

• Let the star drift again. You should notice that it takes longer for the star to begin drifting off the line. Repeat the azimuth adjustments, placing the star back on the crosshair again when finished.

• Continue letting the star drift and making adjustments until the star takes about 5 minutes to drift off the line. Again, ignore any left-right motion. Once the star stays bisected by the line (not just close to the line) for 5 minutes without any drift, your mount is accurately aligned in azimuth. Now you just need to adjust the mount in altitude.

Altitude Adjustment

• Pick a second star in the east, about 20° above the horizon, near the same declination as your first star (near the celestial equator). In other words, move the telescope mostly in right ascension to select the second star. If there are any obstructions on your eastern horizon, it is possible to achieve an accurate alignment using a star up to about 50° above the horizon.

• If you do not have an unobstructed view to the east, a star in the west can be chosen. You must reverse the adjustments below, however, if you use a star in the west.

• Rotate the diagonal so that you are now standing on the south side of the telescope when looking in the eyepiece. Again, this just makes the adjustments easier.

• Orient the crosshairs again as you did above, so that the horizontal crosshairs are parallel to east-west motion and the vertical crosshairs are parallel to north-south motion.

• Place the star on one of the horizontal lines.

• Let the star drift. You should notice some drift after only a minute or so unless you initial rough alignment happened to be very good.

The following directions are the same for all telescopes

• If the star drifts up, use the mount's altitude adjustment knobs to move the mount so that the star appears to move down in the field of view.

• If the star drifts down, use the mount's altitude adjustment knobs to move the mount so that the star appears to move up in the field of view.

• Use the hand-controller to move the star back onto the horizontal line.

• Let the star drift again. You should notice that it takes longer for the star to begin drifting off the line. Repeat the altitude adjustments, placing the star back on the crosshair again when finished.

• Continue letting the star drift and making adjustments until the star takes about 5 minutes to drift off the line. Again, ignore any left-right motion. Once the star stays bisected by the line (not just close to the line) for 5 minutes without any drift, your mount is accurately polar aligned. You are ready to begin imaging the heavens!