MODIFIED ZÜRICH CLASSIFICATIONS


Class A

 

Individual spots or groups of spots that:

 

  • are unipolar
  • have no penumbra

Class B

 

Spot groups that:

 

  • are bipolar
  • have no penumbrae

Class C

 

Spot groups that:

 

  • are bipolar
  • have spots with umbrae – usually on only 1 side of an elongated group

Class D

 

Spot groups that:

 

  • are bipolar
  • have spots with umbrae on both sides of an elongated group
  • have group length less than 10° heliographic longitude

Class E

 

Spot groups that:

 

  • are bipolar
  • have spots with umbrae on both sides of an elongated group
  • have group length between 10° and 15° heliographic longitude

Class F

 

Spot groups that:

 

  • are bipolar
  • have spots with umbrae on both sides of an elongated group
  • have group length greater than 15° heliographic longitude

Class H

 

Individual spots or spot groups that:

 

  • are unipolar
  • have penumbrae