The following was developed for a discussion of polar alignment at a meeting of the Orange County Astronomers' AstroImaging group. Comments and corrections are welcome and may be sent to kodama@alumni.caltech.edu.

Why Polar Align?

• For visual use, being polar aligned means simplified tracking - a constant speed on one axis is all that is required. High power viewing virtually requires tracking.
• For long film exposures or even a sequence of CCD images taken over a long period, polar-aligned tracking avoids rotation of the image. High accuracy alignment is required for long focal lengths, large image areas (e.g. 4x5 film), high resolution, or long exposures.

• Alignment Using Compass & Bubble Level
  • Limited to accuracy of compass and bubble level readings and altitude markings on your mount.
  • Be sure to correct for magnetic deviation from true north when using a magnetic compass.
• Align on Pole Using Main Scope
  • Requires a clear (and reasonably dark) view of the sky near the pole.
  • Mostly useful to northern hemisphere observers.
  • Requires attention to accurate alignment between the scope's optical axis and the mount's mechanical axis.
  • Watch out for optical "flop" in movable mirror systems such as SCT's. Use a mirror lock if possible.
  • Take refraction into account at low latitudes.
  • Calculate celestial pole's offset from reference stars or use a special polar finder reticle.
• Polar Finder Scope
  • May not be available in some mounts.
  • Requires good alignment between the optical axis of the polar finder scope and the mount's mechanical axis.
  • Requires a clear (and reasonably dark) view of the sky near the pole.
  • Mostly useful to northern hemisphere observers.
  • Take refraction into account at low latitudes.
  • Calculate celestial pole's offset from reference stars or use a special polar finder reticle.
  • See the detailed writeup on the use of the Kenko/Losmandy polar finder.
• Reference Star Iteration
  • Depends on setting circle accuracy (highest accuracy on computer-driven scopes with motor encoders)
  • Watch out for optical "flop" in movable mirror systems such as SCT's. Use a mirror lock if possible.

• Drift Alignment - for maximum accuracy in imaging applications or permanent telescope installations.