But a closer look at the surface reveals the largest explosions anywhere in our solar system. Nobody is quite sure what causes them. This week in the journal Nature , three scientists announced they've nailed down a link that could hold some clues. Relating the two is a step toward understanding what triggers them and how to predict them. Ancient Sun Watchers Sunspot sightings have been recorded since 200 B.C. when Chinese astronomers noticed that mysterious dark spots appeared and disappeared on its surface.
Solar fares are also a manifestation of a magnetic field, but they're external.
That the two phenomena both arise from the sun's magnetic field was the first clue that they might be related. The second connection was found in the early 1980s. Centuries of sunspot-watching taught scientists that sunspots to go through cycles, with peaks of activity every 11 years. But there's a shorter cycle, too. It's much less pronounced, but the surface areas of the sunspots get larger and smaller over cycles of approximately five months.