According to Pam Spence in the “Sun Observer’s Guide” sunspots provide useful information about how much solar activity is under-weigh. The sun spots show up in pairs, as dark spots on the visible part of the sun, called the photosphere. Each spot in the pair is a magnetic pole with the magnetic field at those point s averaging from 0.4 Teslas to as much as 1.0 Teslas, according to David Darling in “The Universal Book of Astronomy”. They show up as dark spots because the photosphere is kept cooler by the rise in magnetism. The occurrence of sunspots is usually 30 degrees north and south of the solar equator but they can extend further.
Since 1845, the number of sunspots has been recorded daily and a number known as the relative sunspot number has been calculated. In general, what is used to classify the sunspot number is the count of sunspots, the number of groups of sunspots, and the types of features displayed by the sunspots including whether they pair, their size and color, and how close they cluster together using a system known as the Mt. Wilson scheme that bases the classification on their magnetic properties. This scheme incorporates both the earlier visual Zurich or Waldmeier and the McIntosh Scheme that replaces it.
Alpha or Unipolar
Single spots that vary in density, from one occurrence to many in a group.
Beta or Bipolar
Matched spots in which a line can be drawn to connect the positive-negative pair, varying in density and occurrences.
Beta-Gamma or Clustered Bipolar
Bipolar pairs in a groups so clustered that you can’t attach the positive pole to the negative pole spot, looking like a group of connect the dots with no numbering scheme. They can be shaded or not.
Delta or Shaded Pairs
Bipolar pair where the one part of the pair lies inside the other, from one to many in a group, looking like a shaded area around a pinpoint.
Gamma or Shaded Clusters
Even more complex than the others, this shows pairs clustered inside of each other where you can’t connect the positive to the negative pole of a pair. This looks like a shaded blob with many dark spots inside.
Usually the shaded clustered sunspots are larger than 10 degrees. When deciding how to classify sunspots, its best to provide as much information as possible, or like the MacIntosh does it, each spot has a field for single, pair or cluster.
[1] Pam Spence, Sun Observer’s Guide
[2] David Darling, The Universal Book of Astronomy
