Maunder's Butterfly Diagram

Throughout the solar_cycle, the latitude of sunspot occurrence varies with an interesting pattern. The plot above shows the latitude of sunspot occurrence versus time in years. Sunspots are typically confined to an equatorial belt between -35 degrees south and +35 degrees north latitude.

At the beginning of a new solar cycle, sunspots tend to form at high latitudes, but as the cycle reaches a maximum (large numbers of sunspots) the spots form at lower latitudes. Near the minimum of the cycle, sunspots appear even closer to the equator, and as a new cycle starts again, sunspots again appear at high latitudes.

This recurrent behavior of sunspots gives rise to the ``butterfly'' pattern shown, and was first discovered by Edward Maunder in 1904. The reason for this sunspot migration pattern is unknown. Understanding this pattern could tell us something about how the Sun's internal magnetic field is generated.

You should be able to tell when solar cycle 24 starts by looking at the latitude of the sunspots that form. Today's current crop of sunspots are at or near the sun's equator, so you can conclude they are leftover from cycle 23. The magnetic polarity of the 'new spots' also switches, but it's harder to measure that parameter. However, the measurements confirm, the spots are leftovers.