Sunspots

At the beginning of an active period in the solar cycle, a few sunspots appear at the higher latitudes (i.e., near the poles). These are more or less stationary on the Sun's surface, but appear to us to move because of the Sun's axial rotation. Large spots—which may be large enough to sink many Earths in—may last for one or several solar-rotation periods of about a month each. As the solar cycle progresses, the number of spots increases and they tend to disappear at higher latitudes and appear at lower latitudes (i.e., nearer the equator). The end of the cycle is marked by a marked drop in the number of low-latitude sunspots, which is followed by the beginning of the next cycle as spots begin to appear again at high latitudes.

Sunspots, which usually occur in pairs aligned with the direction of the Sun's spin, correspond to places where intense magnetic fields emerge from or reenter the solar surface. Just as a bar magnet possesses a looping magnetic field connecting one end of the bar to the other, as revealed by iron filings scattered over a sheet of paper placed above the magnet, sunspot pairs possess a magnetic field that links them and along which charged particles align their motion. Scientists label the ends of a bar magnet "north" or "south" magnetic poles depending on their properties; similarly, each member of a sunspot pair corresponds to either a north or south magnetic pole. During a given solar cycle, the member of a sunspot pair that leads (i.e., is located toward the direction of the Sun's rotation) usually has the same magnetic polarity in a pair formed in a particular hemisphere. The order of polarity is reversed for sunspot pairs formed in the opposite hemisphere. The magnetic orientation spot pairs is preserved throughout one entire 11–13 year solar cycle; however, during the next cycle the order of leading and trailing polarities is reversed in both hemispheres. Thus the sunspot cycle actually consists of two 11–13 year cycles, since two cycles must pass before conditions are duplicated and the pattern can begin to repeat.