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Table 1.
Mount Wilson classification rules for grouping solar ARs according to their magnetic complexity.
| Class symbol | Classification rules |
|---|---|
| α | A unipolar sunspot group |
| β | Bipolar sunspot group with |
| a distinct section between polarities | |
| βγ | A bipolar sunspot group |
| whose opposite polarities cannot | |
| be separated with a continuous line | |
| γ | A complex sunspot group with |
| mixed positive and negative polarities, | |
| which cannot be identified as a bipolar | |
| δ | A complex sunspot group |
| that contains opposite polarity | |
| umbrae within the same penumbra |
Notes. Reprinted from van Driel-Gesztelyi & Green (2015, p. 80).
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