The Butterfly Diagram

The construction of sunspot butterfly diagrams was first carried out by E.W. Maunder in 1904, and proceeds as follows:

  • Lay out a coordinate grid with the rotation axis defining the N-S vector.
  • Divide the visible solar disk into latitudinal strips of constant projected area
  • On each strip calculate the percentage of the area covered by sunspots
  • Repeat at time intervals
  • Stack the arrays one beside each other

    These observations include information on the sizes and positions of sunspots as well as their numbers. This data shows that sunspots are not randomly distributed over the surface of the sun, but are concentrated in two latitude bands on either side of the equator.