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April
24, 2007: Astronomers are calling the Japanese Hinode
spacecraft a "Hubble for the sun." Watch this
movie and you'll see why:
Click
to view a 3 MB mpeg movie.
The
footage, gathered by Hinode's Solar Optical Telescope (SOT)
on Dec. 13, 2006, shows sunspot 930 unleashing a powerful
X-class
solar flare. It's one of the most detailed movies of a flare
solar physicists have ever seen. The SOT has a resolution
of 0.2 arcseconds or 0.00006 degrees. Putting those numbers
into perspective, the telescope can see features on the sun
as small as 90 miles wide from its orbit 93 million miles
away.
But
resolution is only part of the story. What makes Hinode truly
special as a solar telescope "is its unique ability to
see the sun's magnetic field," says John Davis, NASA's
project scientist for Hinode at the Marshall Space Flight
Center. It's an ability Hinode used to reveal the magnetic
underpinnings of the Dec. 13th flare.
"Solar
flares are essentially magnetic," Davis explains. In
the maelstrom above a sunspot, lines of magnetic force are
twisted and stretched until the tension reaches a certain
point—and then the whole thing explodes.
A
rubber band provides a good analogy. Take one from your desk,
hold one end in each hand: stretch and twist. If you twist,
twist and twist to extremes, the tormented band will eventually
snap, painfully releasing all the energy you just put into
it.
Magnetic
fields behave a lot like rubber bands, and "Hinode was
able to see the twisting and stretching that preceded the
Dec. 13th solar flare," he says.
 Regard
the animation at right. It looks like a rampaging hurricane--about
twice as wide as Earth! In fact, it is a magnetic map of the
flare zone on the southern flanks of sunspot 930. Red arrows
indicate the direction of the sunspot's magnetic field. White
areas have positive polarity (N); black areas are negative
(S). The movie begins on Dec. 10th, three days before the
flare, and ends on Dec. 14th, one day after the flare.
Right:
A magnetic movie of sunspot 930 shows the tension building
just before the X-flare of Dec. 13, 2006. [Larger
movie]
"These
data were recorded by Hinode's spectro-polarimeter, a device
which can sense magnetic fields by analyzing the polarization
of light coming from iron ions in the sun's atmosphere,"
explains Davis.
The
hurricane, he says, is actually a giant tube of magnetic flux
emerging from beneath the sun's surface. As it spins, lines
of magnetic force become twisted and stretched, while N and
S polarities are shoved together in close proximity. "This
causes a build-up of tension and energy in the magnetic field."
On
Dec. 13, 2006, at precisely 0234 UT, the energy was released
in the form of an X3-category solar flare. The explosion hurled
a coronal mass ejection (CME: a billion-ton cloud of gas)
into space, which sparked Northern Lights as far south as
Arizona when it hit Earth a day later. Shock waves in the
CME accelerated heavy ions to near-light speed, and these
ions coursed around the Earth and Moon for more than a day.
This is called a "radiation storm." If astronauts
had been on the Moon at the time, they may have been forced
to stay indoors—inside their spaceships or habitats—to avoid
exposure.
Astronomers
have been struggling to predict solar flares since flares were
discovered in 1859 by Lord R.C. Carrington and R. Hodgson. But
they have been stymied, in part, by the difficulties of mapping
the sun's magnetic field. Magnetograms on Earth must look through
our planet's turbulent atmosphere, which blurs the little red
arrows we see so clearly in the Hinode movie. Hinode's ability
to examine magnetic fields from Earth orbit is a new and crucial
development.
"The
kind of data we're getting from Hinode is just what we need
to sort out how flares work," says Davis. "All we
need now is some more explosions."
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Hinode is a joint mission of the Japan Aerospace Exploration
Agency (JAXA), the National Astronomical Observatory of Japan
(NAOJ), the National Aeronautics and Space Administration
(NASA) and the Particle Physics and Astronomy Research Council
(PPARC). The Marshall Space Flight Center managed the NASA
instrument component integration for NASA Headquarters, is
managing the science operations for NASA and is also supporting
science operations in Japan.
Author: Dr.
Tony Phillips | Production Editor:
Dr. Tony Phillips | Credit: Science@NASA
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