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 aurora s, and may pose a radiation hazard to astronauts.