What is it?

• Aligning your mount's polar axis with the north celestial pole.
  
• Aligning your mount with the celestial coordinate system.
  
• RA/Dec is the celestial system, Alt/Az is the terrestrial system.
  
• You must align the mount to the celestial system by adjusting its Alt/Az positions.
• Polaris is not at the NCP, it's coordinates are RA 2h32m, Dec 89.25°
  

Why do it?

• Only fixes star drift in Dec (north-south).
  
• Error in RA is caused by clock drive inaccuracy, not polar alignment.
  
• For tracking and guiding, just need to get Dec better than RA (east-west) error.
  
• Poor polar alignment also causes field rotation.
  
• Must have more accurate polar alignment to reduce field rotation in long exposures.
  

How accurate do I need it?

• Accuracy is measured in minutes without noticeable star drift.
  
• Requirements depend on length of exposure and field of view.
  
• Larger field of view requires better alignment to reduce noticable field rotation.
  
• Typically a 5-minute polar alignment accuracy is required for 60-minute exposures with a 1° field of view.

How to do it?

• Adjust the mount's altitude to your latitude (38° in Charlottesville) and azimuth to North.
  
• Rough Alignment is done by just "eyeballing" your polar axis to Polaris. This is good enough for typical visual observing.
  
• For more accurate alignment:
  
  • Using a Polar Alignment Scope
    
  • Using Clay's Kochab Clock
    
  • Using the Drift Method
    

Excellent References

• Drift Method of Polar Alignment by Chuck Vaughn
  
• Polar Aligning by Jerry Lodriguss