Sunspots - Observational Clues of the Solar Cycle

Look again at the Sun's face -- those darned spots!

What causes them? What do they tell us about the Sun? Let's take some data...

Sunspot appearance

Sunspots are sociable critters. They appear in pairs or groups, not alone.

Individual spots come and go, and the numbers of sunspots varies with time. If we plot the number of sunspots as a function of time, it is not random -- it shows an 11 year cycle of highs and lows.

The latitude of sunspots also changes with time. Early in the cycle, spots appear at more extreme (northerly, southerly) latitudes, and as the cycle advances and more spots appear, the tend to appear more towards the equator.

Remember: the spots themselves don't move towards the equator -- it's just that, on average, the form closer to the equator as the cycle progresses.

Sunspot regions are cooler (~3900 K) than their surrounding areas (~5800 K). Because they are cooler, they don't emit as much energy, and are fainter.

Sunspots are regions of strong magnetic fields, with the polarity being different between leading and trailing spots in a group. The sense of polarity switches with every cycle, so the 11 year cycle is really a 22 year cycle!