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This disappearing act is possible because sunspots are made of
magnetism. The
“firmament” of a sunspot is not matter but rather a strong
magnetic field that appears
dark because it blocks the upflow of heat from the sun’s
interior. If Earth lost its
magnetic field, the solid planet would remain intact, but if a
sunspot loses its
magnetism, it ceases to exist.
“According to our measurements, sunspots seem to form only if
the magnetic field
is stronger than about 1500 gauss,” says Livingston. “If the
current trend continues,
we’ll hit that threshold in the near future, and solar magnetic
fields would become
too weak to form sunspots.”
"This work has caused a sensation in the field of solar
physics,” comments NASA
sunspot expert David Hathaway, who is not directly involved in
the research. “It’s
controversial stuff.”
If sunspots do go away, it wouldn’t be the
first time. In the 17th century, the sun
plunged into a 70-year period of spotlessness known as the
Maunder Minimum
that still baffles scientists. The sunspot drought began in 1645
and lasted until 1715;
during that time, some of the best astronomers in history (e.g.,
Cassini) monitored
the sun and failed to count more than a few dozen sunspots per
year, compared to
the usual thousands.
“Whether [the current downturn] is an omen
of long-term sunspot decline,
analogous to the Maunder Minimum, remains to be seen,”
Livingston and Penn
caution in a recent issue of EOS. “Other indications of solar
activity suggest that
sunspots must return in earnest within the next year.”
See entire article:
http://science.nasa.gov/headlines/y2009/03sep_sunspots.htm
Thanks to Andrew Johnson for this link |
