A solar flare is a sudden release of energy, usually associated with an active sunspot group. The most spectacular of all solar flare phenomena are called prominences. A typical active prominence has a height of about 60,000 kilometres.

Sunspots are dark patches that occur on the sun's visible surface (photosphere), usually in groups and with a lifetime of several weeks. They are regions of relatively cool gas and their presence is associated with local variations in that area of the sun's magnetic field. The number of sunspots fluctuates over a period of about 11 years per hemisphere (hence the total cycle is around 22 years). Sunspots contain strong magnetic fields, and usually occur in groups of pairs in which the leading spot and the following spot of the pair have opposite magnetic polarity. They tend to occur at a latitude of 45 degrees.

As the solar flare erupts from these active sun spot regions, it ejects high-velocity particles (usually electrons) and masses of material. These travel along with the solar wind (stream of ionised particles emitted by the sun in all directions). If they reach Earth they will interact with its magnetic field and may cause heightened magnetic storms and aurorae (northern lights). It has been suggested that the particles emitted by flares may present a hazard to astronauts who are in space or on the unprotected surface of the Moon. The Earth's magnetic field and atmosphere protect us from the worse emissions from the sun.