Zurich Sunspot Class: A
A small single unipolar sunspot. Representing either the
formative or final stage of evolution.
Zurich Sunspot Class: B
Bipolar sunspot group with no penumbra on any of the
spots.
Zurich Sunspot Class: C
A bipolar sunspot group. One sunspot must have penumbra.
Zurich Sunspot Class: D
A bipolar sunspot group with penumbra on both ends of
the group. Longitudinal extent does not exceed 10 deg.
Zurich Sunspot Class: E
A bipolar sunspot group with penumbra on both ends.
Longitudinal extent exceeds 10 deg. but not 15 deg.
Zurich Sunspot Class: F
An elongated bipolar sunspot group with
penumbra on both ends. Longitudinal extent
of penumbra exceeds 15 deg.
Zurich Sunspot Class: H
A unipolar sunspot group with penumbra.
Zurich Sunspot Class: J
('A small H': a unipolar sunspot group with penumbra.
Mount Wilson magnetic class: alpha
A unipolar sunspot group
Mount Wilson magnetic class: beta
A sunspot group having both positive and negative magnetic
polarities, with a simple and distinct division between
the polarities.
Mount Wilson magnetic class: beta-gamma
A sunspot group that is bipolar but in which no
continuous line can be drawn separating spots of opposite
polarities.
Mount Wilson magnetic class: delta
A complex magnetic configuration of a solar sunspot
group consisting of opposite polarity umbrae
within the same penumbra.
Mount Wilson magnetic class: gamma
A complex active region in which
the positive and negative polarities are so irregularly
distributed as to prevent classification as a bipolar group.