Solar flares occur when the Sun releases a burst of energy. They are usually associated with sunspots and magnetic activity. The Sun's magnetic field, usually near a sunspot, releases a burst of energy, which includes significant amounts of ultraviolet and X-ray energy.

Solar astronomers classify solar flares according to the amount of X-ray energy released. The most energetic solar flares are the X class solar flares. M class solar flares are the medium level. C class solar flares are minor flares. Each class of solar flare is subdivided into subclasses from 1 to 9. The higher numbers indicate more energy is released. For example an M9 solar flare releases more energy than an M5 solar flare but less energy than an X class solar flare. The strongest solar flares would be X9 class.

C class flares do not significantly affect Earth. X class solar flares can produce major geomagnetic storms and significantly disrupt radio communication on Earth. They can also cause significant aurora activity. M class solar flares can produce minor geomagnetic storms with high latitude aurora and minor radio disruptions.