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Solar Flares

The Angry Sun

by Richard Erwin

Editor's Note: Here is an explanation for those of use who became fascinated by the unusual sunspot activity in October 2003.

Despite the sun's remarkable stability for almost five billion years, astronomers know that the sun is actually an active body that periodically erupts with considerable violence. These events are associated with sunspots--large areas which appear dark because they are cooler than the surrounding surface.

Scientists know that sunspots are caused by the sun's magnetic field, which grows stronger and weaker over a period of about eleven years. These peaks and valleys, which result in more or fewer spots, are called "solar maximum" and "solar minimum." The most recent solar maximum occurred in the spring of 2000, and we are now well into a period of what should be declining solar activity. But something very strange has happened.

Aurora over Boston during the height of sunspot activityBeginning on October 19, 2003, the sun's surface activity began to heat up unexpectedly. A huge new sunspot suddenly appeared that promptly spawned a major solar flare at . These flares sometimes cause the solar corona--a region of hot ionized particles surrounding the sun--to eject a 'bubble' of material outward into space at high velocity. While the corona radiates material away from the sun at all times, these sudden outbursts of particles, called coronal mass ejections (CME), travel much faster and create unusual and varying effects upon the inner planets, including the earth.

On October 22, a second sunspot appeared while the first one grew to amazing size. Then a third spot appeared and produced a flare that triggered a CME. This event prompted astronomers to predict widespread auroral activity for October 25, and in fact, northern lights were seen that night as far south as Arizona.

October 26 saw more activity, including two more flares with associated CMEs, and on October 28, an extremely intense flare erupted, causing scientists to predict more northern lights. This flare, about 1,700 times as powerful as ordinary ones, caused X-rays to bombard the earth's ionosphere strongly enough to cause a dip in the earth's magnetic field.The sun's corona

On October 29, one of the two huge sunspots produced another massive flare and CME, seen in southern California through the smoke from forest fires burning at the time. Resulting radiation that reached the earth caused problems with satellites in orbit and disrupted some communication devices.

On November 3, more flares erupted but the best was yet to come! At about on November 4, a sunspot complex (identified as 10486) on the sun exploded with what may have been the most intense X-ray flare in history. Detectors onboard orbiting spacecraft were unable to measure its true intensity due to saturation, but it is believed to be twice as strong as anything ever observed before.

The sunspot complex spawning these events has now rotated beyond our view, but it remains to be seen what the sun holds in store for us in the future. We still have much to learn about the nature of our star.

Richard Erwin is an associate professor of computer science and an avid sky watcher who is the adviser for Westminster's Astronomy Club.