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Sudden intense brightening of a small part of the Sun's surface, often near a sunspot group. Flares develop in a few minutes and may last several hours, releasing intense X rays and streams of energetic particles. They appear to be connected with changes in the Sun's magnetic fields during the solar cycle. The ejected particles take a day or two to reach the vicinity of Earth, where they can disrupt radio communications and cause auroras, and may pose a radiation hazard to astronauts.
This entry comes from Encyclopædia Britannica Concise. For the full entry on solar flare, visit Britannica.com.