Mount Wilson Magnetic Classifications

Alpha. Denotes a unipolar sunspot group. Beta. A sunspot group having both positive and negative magnetic polarities, with a simple and distinct division between the polarities. Beta-Gamma. A sunspot group that is bipolar but in which no continuous line can be drawn separating spots of opposite polarities. Delta. A complex magnetic configuration of a solar sunspot group consisting of opposite polarity umbrae within the same penumbra . Gamma. A complex active region  in which the positive and negative polarities are so irregularly distributed as to prevent classification as a bipolar group.