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Nov.
7, 2008: After two-plus years of few sunspots, even
fewer solar flares, and a generally eerie calm, the sun is
finally showing signs of life.
"I
think solar minimum is behind us," says sunspot forecaster
David Hathaway of the NASA Marshall Space Flight Center.
His
statement is prompted by an October flurry of sunspots. "Last
month we counted five sunspot groups," he says. That
may not sound like much, but in a year with record-low numbers
of sunspots and long stretches of utter spotlessness, five
is significant. "This represents a real increase in solar
activity."
Above:
New-cycle sunspot group 1007 emerges on Halloween and marches
across the face of the sun over a four-day period in early
November 2008. Credit: the Solar and Heliospheric Observatory
(SOHO).
Even
more significant is the fact that four of the five sunspot
groups belonged to Solar Cycle 24, the long-awaited next installment
of the sun's 11-year solar cycle. "October was the first
time we've seen sunspots from new Solar Cycle 24 outnumbering
spots from old Solar Cycle 23. It's a good sign that the new
cycle is taking off."
Old
Solar Cycle 23 peaked in 2000 and has since decayed to low levels.
Meanwhile, new Solar Cycle 24 has struggled to get started.
2008 is a year of overlap with both cycles weakly active at
the same time. From January to September, the sun produced a
total of 22 sunspot groups; 82% of them belonged to old Cycle
23. October added five more; but this time 80% belonged to Cycle
24. The tables have turned.
At
first glance, old- and new-cycle sunspots look the same, but
they are not. To tell the difference, solar physicists check
two things: a sunspot's heliographic latitude and its magnetic
polarity. (1) New-cycle sunspots always appear at high latitude,
while old-cycle spots cluster around the sun's equator. (2)
The magnetic polarity of new-cycle spots is reversed compared
to old-cycle spots. Four of October's five sunspot groups
satisfied these two criteria for membership in Solar Cycle
24.
The
biggest of the new-cycle spots emerged at the end of the month
on Halloween. Numbered 1007, or "double-oh seven"
for short, the sunspot had two dark cores each wider than
Earth connected by active magnetic filaments thousands of
kilometers long. Amateur astronomer Alan Friedman took this
picture from his backyard observatory in Buffalo, New York:
On
Nov. 3rd and again on Nov. 4th, double-oh seven unleashed
a series of B-class solar flares. Although B-flares are considered
minor, the explosions made themselves felt on Earth. X-rays
bathed the dayside of our planet and sent waves of ionization
rippling through the atmosphere over Europe. Hams monitoring
VLF radio beacons noticed strange "fades" and "surges"
caused by the sudden ionospheric disturbances.
Hathaway
tamps down the excitement: "We're still years away from
solar maximum and, in the meantime, the sun is going to have
some more quiet stretches." Even with its flurry of sunspots,
the October sun was mostly blank, with zero sunspots on 20
of the month's 31 days.
But
it's a start. Stay tuned for solar activity.
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Author: Dr.
Tony Phillips | Credit: Science@NASA
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