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Normal Stars

The intense heat in the atmosphere of stars like the Sun frees some of the electrons from their atoms. Because of this, the magnetic fields are dragged along with the rising and falling gas. An additional complication is that the star is rotating. The up-and-down motion, coupled with the round and round motion of rotation, twists the magnetic field and increases its strength. Twisted, magnetized tubes of gas rise high above the surface of the star. There they unwind, releasing stored energy. (Try twisting and untwisting a rubber band and you get an idea of this process.)

The release of magnetic energy can occur steadily and provide for the heating of the tubes of hot gas which make up the stellar corona. Or it can occur violently and produce flares. Flares can occur on the Sun at any time, but their frequency tends to rise from a peak of five to ten a day and fall to less than one per day in a cycle of about eleven years. Solar flares can shower the Earth in high-energy particles. A strong one can disrupt radio communications and produce spectacular displays known as the Northern and Southern Lights. Flares may even have a subtle but important effect on our weather.

Sun with huge solar flare Photograph of the Sun, taken during final mission of NASA's Skylab.
(Credit: NRL)
This photograph of the Sun, taken on December 19, 1973 during the third and final manned Skylab mission, shows one of the most spectacular solar flares ever recorded, spanning more than 588,000 kilometers (365,000 miles) across the solar surface. The flare gives the distinct impression of a twisted sheet of gas in the process of unwinding itself. The photograph was taken by the extreme ultraviolet spectroheliograph instrument of the U.S. Naval Research Laboratory.)

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