A flare is a sudden, intense burst of bright light and heat. It is the most common type of solar activity and can last from minutes to hours. Flares occur when the sun’s magnetic field lines become twisted and release their energy. This can happen when two opposite magnetic fields connect or when one magnetic field collapses. The released energy heats up the plasma in the sun’s atmosphere, causing it to expand and emit light.
Flares are classified according to their intensity. The weakest flares are A-class flares, while the strongest are X-class flares. X-class flares are very rare, occurring only once or twice per year. They can cause widespread damage to power grids and communications systems, and can even disrupt the Earth’s upper atmosphere.
Solar activity goes through an 11-year cycle, with more flares occurring during the peak of the cycle (known as solar maximum) than during the lulls (solar minimum). However, even during solar minimum there can be sporadic flare activity. So far in 2020, there have been several M-class flares – none of which have been particularly strong – but no X-class flares as of yet.
While most people think of the sun as being yellow, it actually emits a wide range of colors depending on its temperature. The colors emitted by a flare depend on its temperature as well; hotter flames tend to be blue or violet, while cooler ones appear redder.
When viewed from Earth using special telescopes that allow us to see ultraviolet light, some parts of a flare look like ribbons or arches extending out from the sun’s surface along its magnetic field lines