Post-flare loop above the Sun's surface, false colour photograph by Skylab, 1973.

Solar flares are sudden outbursts of energy originating on the Sun's surface and projecting far into its atmosphere. They occur near sunspots on boundaries dividing areas with opposite magnetic fields. Temperatures inside flares can reach tens of millions of degrees Kelvin, and masive amounts of radiation are released acros the whole electromagnetic spectrum. The emisions from large flares can cause radio blackouts on Earth, and can be dangerous to astronauts beyond the protection of the Earth's atmosphere. These loop-shaped structures are often seen after the eruption of a flare, and are thought to be material condensing back out of the corona, the very hot region upper part of the Sun's atmosphere, and returning to the surface.