If you've ever stood in front of a hot stove, watching a pot of water and
waiting impatiently for it to boil, you know what it feels like to be a solar
physicist.
Back in 2008, the solar cycle plunged into the deepest minimum in nearly a
century. Sunspots all but vanished, solar flares subsided, and the sun was
eerily quiet.
"We've been waiting for solar activity to pick up," says Richard Fisher, head of
the Heliophysics Division at NASA Headquarters in Washington DC. "We've been
waiting three long years."
Quiet spells on the sun are nothing new. They come along every 11 years or so —
it's a natural part of the solar cycle. This particular solar minimum, however,
was lasting longer than usual, prompting some researchers to wonder if it would
ever end.
Now the pot is starting to boil. "Finally," says Fisher, "we are beginning to
see some action."
As 2011 unfolds, sunspots have returned and they are crackling with activity. In
February and March, Earth orbiting satellites detected a pair of "X-flares" —
the brightest x-ray solar flares since 2006.
Another eruption in March hurled a billion-ton cloud of plasma away from the sun
at five million miles per hour (2200 km/s). The rapidly expanding cloud, known
as a "coronal mass ejection," wasn't aimed directly at Earth, but it did deliver
a glancing blow to our planet's magnetic field. The off-center impact was enough
to send Northern Lights spilling over the Canadian border into US states such as
Wisconsin, Minnesota, and Michigan.
"That was the fastest coronal mass ejection in almost six years," says Angelos
Vourlidas of the Naval Research Lab in Washington DC. "It reminds me of a
similar event back in November 1997 that kicked off Solar Cycle 23. I'd say
Solar Cycle number24 is now underway."
The slow build-up to this moment is more than just "the watched pot failing to
boil," says Ron Turner, a space weather analyst at Analytic Services, Inc. "It
really has been historically slow."
There have been 24 numbered solar cycles since astronomers started keeping track
of them in the 18th century. An analysis just published by Turner in the journal
Space Weather shows that, in all that time, only four cycles have started more
slowly than this one.
Better late than never.
For more information about solar activity and other hot topics, visit
science.nasa.gov.
Документальный фильм "Solar Activity Heats Up"
