Space Weather Classification System
Solar flares are classified according to their intensity, or energy output. The classes range from A, which are the weakest flares and barely noticeable above the Sun’s background radiation, through B, C, and M, up to X, which are the strongest flares. Each higher class is a 10-fold increase in energy. So an X flare is 10 times stronger than an M flare and 100 times stronger than a C flare.