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 a streams of highly energetic
solar wind that can present a
radiation hazard to spacecraft
outside of
planetary magnetospheres 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 fewer 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.
Energetic particles emitted by solar flares are a primary contributor
to the aurora borealis and aurora australis.
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.
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