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