solar flare

A solar flare is a sudden, intense flash of energy on the Sun, a brilliant burst of light and radiation that erupts from a magnetically active region in a matter of minutes. It is the Sun's equivalent of a lightning storm, but powered by tangled magnetic fields rather than rain clouds.

Flares happen when the twisted magnetic field above a sunspot group snaps into a simpler shape, a process called magnetic reconnection, releasing a huge store of energy all at once. That energy heats the local gas to tens of millions of degrees and accelerates particles to enormous speeds, producing a flash of radiation across the whole spectrum — radio waves, visible light, ultraviolet, and especially X-rays. The biggest flares are classified as X-class and can release on the order of 10^25 joules, comparable to many millions of large volcanic eruptions, in just minutes. The light and X-rays travel at the speed of light, so they reach Earth in about 8 minutes, with no warning.

Solar flares matter for space weather. Their burst of X-rays and ultraviolet light can ionise Earth's upper atmosphere and disrupt radio communications and GPS within minutes, and the high-energy particles some flares fling out pose a radiation hazard to astronauts and spacecraft. Flares often, but not always, come together with a coronal mass ejection — a related but distinct event.