A phenomenon in the solar chromosphere and corona, caused by a sudden release of energy that heats and accelerates matter in the Sun’s atmosphere. Flares are explosions lasting typically for a few minutes, during which matter reaches temperatures of hundreds of millions of degrees. Most of the radiation is emitted as X-rays but flares are more easily observed in visible light or radio waves. They are associated with active regions of the Sun. Charged particles ejected from the Sun by flares cause aurorae when they reach the Earth a few days later.