Unless you are lucky enough to live in a dark location and have a permanent observatory, you will have to accurately polar align your telescope each and every time you go out.

Why?

An accurate polar alignment is required to eliminate "field rotation".  A perfectly guided astrophoto will still show error if the mount is not very accurately polar aligned.  Field rotation shows up in an image as curved stars at the outer edges of the image.  This is not to be mistaken for coma, usually seen in fast camera lenses, in which the stars are bloated little UFO-like things.  A well-aligned mount will not show field rotation.

How?

The following procedure for the drift method of polar alignment assumes the use of a Schmidt-Cassegrain (SCT) or refractor telescope.  If you are using a Newtonian for photography you will simply need to reverse the adjustment steps.  These steps are highlighted for you.

Once you have read through the following detailed procedure you may wish to print out the Quick Guide to Drift Alignment to have with you in the field.

Note:  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.

View through a double-crosshair illuminated reticle eyepiece

The telescope mount should already be roughly polar aligned, preferably using a polar alignment scope.

• The drift alignment requires that you let the telescope track on two different stars are specific locations in the sky.  Watching how the stars drift relative to the reticle in the crosshair eyepiece tells how far the mount is offset from true celestial north and in which direction.  Click here if you would like to learn the theory behind the drift alignment.
   
• Pick a star near the meridian, just north of the celestial equator (due south, between about 60°-70° above the horizon).  Select a star that is reasonably bright but not too bright (about magnitude 5-6).  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, placing the telescope on the west side of the mount.  Rotate the diagonal (if using an SCT or refractor) until the eyepiece is oriented so that you are standing on the north side of the telescope when looking into the eyepiece.  These steps are not absolutely necessary but will make the following procedure easier.
   
• The eyepiece's crosshairs 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 (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.
   

  Place star on east-west line

• 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.
   

  
   
   

  Star drifts up	Adjust mount to move star to right

• 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.
   
• Pick a second star in the east, about 20° above the horizon, near the same declination as your first star (near the celestial equator).  If your telescope was on the west side of the mount during the first half of the alignment you can just move it in right ascension.  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.

Reverse the following adjustments if you are using a Newtonian telescope

• 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.
   

  Star drifts up	Adjust mount so star moves down

• 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!