It may sound hard to believe on a hot summer day, but the Sun has been unusually quiet over the last few years. In fact, it's just coming out of its quietest period in almost a century.
The Sun's magnetic field goes through a cycle that lasts an average of about 11 years. At the cycle's peak, the Sun's surface is covered with dark magnetic storms known as sunspots. It also produces big eruptions of energy and particles that can damage satellites, disrupt communications, and knock out power grids here on Earth.
Between these peaks, the Sun gets quiet -- there are far fewer sunspots and flare-ups. These periods are known as solar minimum, and the last one, which ended just last year, was one of the quietest on record. It produced the fewest sunspots seen since 1913, for example. And it ended with a stretch of about 10 months without a single sunspot, which also hadn't happened since 1913.
And it had one other effect: it let in more radiation from beyond the solar system. The Sun produces a "wind" of charged particles that fill the solar system like a magnetic balloon. During solar minimum, though, the solar wind is thinner and slower. That allows particles known as cosmic rays to infiltrate the solar system. And that's just what happened during the last solar minimum -- the number of cosmic rays was highest since astronomers began watching them in the 1950s.
The next solar cycle could be quiet, too, and we'll talk about that tomorrow.
Script by Damond Benningfield, Copyright 2010
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