A solar flare is an intense burst of radiation coming from the release of magnetic energy associated with sunspots. It is a tremendous explosion on the Sun that happens when energy stored in twisted' magnetic fields (usually above sunspots) is suddenly released. Flares occur in active regions and are often, but not always, accompanied by coronal mass ejections, solar particle events, and other solar phenomena. The occurrence of solar flares varies with the 11-year solar cycle. Solar flares are thought to occur when stored magnetic energy in the Sun's atmosphere accelerates charged particles in the surrounding plasma. This results in the emission of electromagnetic radiation across the electromagnetic spectrum. The plasma medium is heated to tens of millions of kelvins, while electrons, protons, and heavier ions are accelerated to near the speed of light.

Solar flares affect all layers of the solar atmosphere (photosphere, chromosphere, and corona) . They heat material to many millions of degrees and produce a burst of radiation across the electromagnetic spectrum, including from radio waves to x-rays and gamma rays. Scientists classify solar flares according to their brightness in the x-ray wavelengths. 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. There are five classes of solar flares, according to NOAA. Their designation depends on the intensity of X-rays emitted. Each class letter represents a 10-fold increase.