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NASA News: Are Sunspots Disappearing?

3 Sep 09 – (Excerpts) The sun is in the pits of the deepest solar minimum in nearly a century. Weeks and sometimes whole months go by without even a single tiny sunspot. The quiet has dragged out for more than two years, prompting some observers to wonder, are sunspots disappearing?

“Personally, I’m betting that sunspots are coming back,” says researcher Matt Penn of the National Solar Observatory (NSO) in Tucson, Arizona. But, he allows, “there is some evidence that they won’t.”

Penn’s colleague Bill Livingston of the NSO has been measuring the magnetic fields of sunspots for the past 17 years, and he has found a remarkable trend. Sunspot magnetism is on the decline.

Above: Sunspot magnetic fields measured by Livingston and Penn from 1992 - Feb. 2009 using an infrared Zeeman splitting technique. [more]

“Sunspot magnetic fields are dropping by about 50 gauss per year,” says Penn. “If we extrapolate this trend into the future, sunspots could completely vanish around the year 2015.”

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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:
Thanks to Andrew Johnson for this link


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