A sunspot pair or group in which the leading and following spots (in the sense of solar rotation) have opposite magnetic polarities. The polarities obey Hale's law (named after G. E. Hale), which states that the leading and following spots have opposite polarities on either side of the equator. These polarities are reversed in each successive sunspot cycle. On the Mount Wilson sunspot classification system, bipolar groups are denoted by the Greek letter β.
Subjects: Astronomy and Astrophysics.