A solar flare is a tremendous explosion on the Sun that happens when energy stored in twisted magnetic fields (usually above sunspots) is suddenly released. It is an intense burst of radiation coming from the release of magnetic energy associated with sunspots. Flares are our solar systems largest explosive events and are seen as bright areas on the sun that can last from minutes to hours. Flares emit electromagnetic radiation across the electromagnetic spectrum at all wavelengths, from radio waves to gamma rays. The plasma medium is heated to >107 kelvin, while electrons, protons, and heavier ions are accelerated to near the speed of light. Scientists classify solar flares according to their brightness in the x-ray wavelengths, and there are three categories: X-class flares are big; they are major events that can trigger radio blackouts around the whole world and long-lasting radiation storms in the upper atmosphere.

Solar flares tend to originate from regions of the solar surface that contain sunspots, which are darker, cooler portions of the solar surface where magnetic fields are particularly strong. The number of sunspots can indicate the likelihood of a solar flare eruption. Solar flares are different from coronal mass ejections (CMEs), which were once thought to be initiated by solar flares. CMEs are huge bubbles of gas threaded with magnetic field lines that are ejected from the Sun over the course of several hours. Although some are accompanied by flares, it is now known that most CMEs are not associated with flares.

Solar flares can have a range of effects on Earth, including radio blackouts, power outages, and damage to communication satellites. NASA and other organizations keep a constant watch on the sun to monitor for X-class flares and their associated magnetic storms. During periods of low solar activity when no sunspots are present, it is unlikely that a solar flare will occur.