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Kate Wong Scientific American
Late
Monday, the Solar and Heliospheric Observatory spotted an
enormous prominence just before it collapsed over the Sun's
southwestern limb. The event hurled a bright coronal mass
ejection (CME) into space -- but not toward Earth. Click
here to view a 400 kb animation of the CME. In the movie,
the star-like object moving away from the Sun's southeast
limb is the planet Mercury.
"Filaments
are formed in magnetic loops that hold relatively cool,
dense gas suspended above the surface of the Sun,"
explains David Hathaway, a solar physicist atthe NASA Marshall
Space Flight Center. "When you look down on top of
them they appear dark because the gas inside is cool compared
to the hot photosphere below. But when we see a filament
in profile against the dark sky it looks like a giant glowing
loop -- these are called prominences and they can be spectacular."
Right:
Last year extreme ultraviolet
cameras on board the orbiting Solar and Heliospheric Observatory
captured this image of a prominence above the eastern limb
of the Sun.
"Filaments
collapse when the magnetic field in their vicinity becomes
unstable," explained Hathaway. "This could happen,
for example, if new magnetic field lines begin to poke through
the Sun's surface beneath the filament." The resulting
explosions, which often occur well away from spotted regions,
are called Hyder flares, named for Charles Hyder, who published
studies of such events in 1967.
For
example:
On October
9, 2000, magnetic fields around sunspot group 9182 suddenly
changed their shape, leading to the explosive collapse of
a nearby magnetic filament suspended high above the Sun's
surface. These hydrogen-alpha pictures from the NOAA/SEC
daily image archive show the location of the filament before
and after the explosion. The collapse triggered a C7-class
solar flare and a full halo coronal mass ejection that struck
Earth's magnetosphere 3 days later.
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