Latest image of the far side of the Sun based on high resolution STEREO data, taken on February 2, 2011 at 23:56 UT when there was still a small gap between the STEREO Ahead and Behind data. This gap will start to close on February 6, 2011, when the spacecraft achieve 180 degree separation, and will completely close over the next several days. Credit: NASA |
It’s official: The sun is a sphere.
On
Feb. 6th, NASA’s twin STEREO probes moved into position on opposite
sides of the sun, and they are now beaming back uninterrupted images of
the entire star—front and back.
“For
the first time ever, we can watch solar activity in its full
3-dimensional glory,” says Angelos Vourlidas, a member of the STEREO
science team at the Naval Research Lab in Washington, DC.
NASA released a ‘first light’ 3D movie on, naturally, Super Bowl Sunday:
“This
is a big moment in solar physics,” says Vourlidas. “STEREO has revealed
the sun as it really is–a sphere of hot plasma and intricately woven
magnetic fields.”
Each
STEREO probe photographs half of the star and beams the images to
Earth. Researchers combine the two views to create a sphere. These
aren’t just regular pictures, however. STEREO’s telescopes are tuned to
four wavelengths of extreme ultraviolet radiation selected to trace key
aspects of solar activity such as flares, tsunamis and magnetic
filaments. Nothing escapes their attention.
An artist’s concept of STEREO spacecraft. Credit: NASA |
“With
data like these, we can fly around the sun to see what’s happening over
the horizon—without ever leaving our desks,” says STEREO program
scientist Lika Guhathakurta at NASA headquarters. “I expect great
advances in theoretical solar physics and space weather forecasting.”
Consider
the following: In the past, an active sunspot could emerge on the far
side of the sun completely hidden from Earth. Then, the sun’s rotation
could turn that region toward our planet, spitting flares and clouds of
plasma, with little warning.
“Not
anymore,” says Bill Murtagh, a senior forecaster at NOAA’s Space
Weather Prediction Center in Boulder, Colorado. “Farside active regions
can no longer take us by surprise. Thanks to STEREO, we know they’re
coming.”
NOAA
is already using 3D STEREO models of CMEs (billion-ton clouds of plasma
ejected by the sun) to improve space weather forecasts for airlines,
power companies, satellite operators, and other customers. The full sun
view should improve those forecasts even more.
The forecasting benefits aren’t limited to Earth.
“With
this nice global model, we can now track solar storms heading toward
other planets, too,” points out Guhathakurta. “This is important for
NASA missions to Mercury, Mars, asteroids … you name it.”
NASA
has been building toward this moment since Oct. 2006 when the STEREO
probes left Earth, split up, and headed for positions on opposite sides
of the sun (movie). Feb. 6, 2011, was the date of “opposition”—i.e.,
when STEREO-A and -B were 180 degrees apart, each looking down on a
different hemisphere. NASA’s Earth-orbiting Solar Dynamics Observatory
is also monitoring the sun 24/7. Working together, the STEREO-SDO fleet
should be able to image the entire globe for the next 8 years.
The
new view could reveal connections previously overlooked. For instance,
researchers have long suspected that solar activity can “go global,”
with eruptions on opposite sides of the sun triggering and feeding off
of one another. Now they can actually study the phenomenon. The Great
Eruption of August 2010 engulfed about 2/3rd of the stellar surface with
dozens of mutually interacting flares, shock waves, and reverberating
filaments. Much of the action was hidden from Earth, but plainly visible
to the STEREO-SDO fleet.
“There
are many fundamental puzzles underlying solar activity,” says
Vourlidas. “By monitoring the whole sun, we can find missing pieces.”
Researchers
say these first-look whole sun images are just a hint of what’s to
come. Movies with even higher resolution and more action will be
released in the days and weeks ahead as more data are processed. Stay
tuned!
