Solar flare
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A solar flare is a violent eruption that explodes from a star's photosphere with energies equivalent to tens of millions of hydrogen bombs. Solar flares from the Sun send out streams of highly energetic solar wind that can present a radiation hazard to spacecraft outside of a planetary magnetosphere and can disrupt radio signals on Earth. Solar flares were first observed on the Sun in 1859 by English astronomer Richard Carrington. They have also been observed to varying degrees on other stars in modern times. The frequency of solar flares varies, from several per day when the Sun is particularly "active" to less than one each week when the Sun is "quiet". Solar flares may take several hours or even days to build up, but the actual flare takes only a matter of minutes to release its energy. The resulting shockwaves travel laterally through the photosphere and upward through the chromosphere and corona at speeds on the order of 5,000,000 kilometers per hour. Solar activity is classified as A, B, C, D, M or X according to the brightness of its X-rays near Earth, measured in W/m\uffff. Each class is ten times more powerful than the preceding one, with X at 10-4 W/m\uffff. Within a class there is a linear scale from 1 to 9, so an X2 flare (twice as powerful as an X1 flare) is four times more powerful than an M5 flare (five times as powerful as an M1 flare). Solar activity is normally within the A to C range. Class D flares have little effect on Earth, while the more powerful M and X flares can cause disruption and damage. Flares generally stay below X10, but infrequently X designations run 'off the charts'. X20 events that were recorded on August 16, 1989 and April 2, 2001 were outshone by a flare on November 4, 2003 that was the most powerful flare ever recorded in the history of astronomy: an X28. Sunspot Region 486 (shown in the illustration) was the most turbulently active sunspot ever recorded.
Energetic particles emitted by solar flares are a primary contributor to the aurora borealis and aurora australis. See also Solar proton event.
The radiation risk posed by solar flares is one of the major concerns in discussions of manned missions to Mars. Some kind of physical or magnetic shielding will be required.
See also: Coronal mass ejection
Solar flare 2003-10-28: from NASA |
External links
de:Flare fr:Éruption solaire it:Flare nl:Zonnevlam ja:フレア pl:Burze słoneczne zh:耀斑
