NUMBER 6
The Sun's Hot Atmosphere
|
Ultraviolet-light image of coronal loops, large arcs of
gas and energetic particles that make up the Sun's corona, as seen by the
TRACE satellite telescope.
|
Hold
your hands near a campfire -- in its "atmosphere," we'll say -- and
they get warm. The closer you get, the warmer it is. If you stick your hands in
the fire (and we don't recommend it) you would find it even hotter.
Likewise, you might expect the Sun to be hottest in the middle, and
then get cooler as you moved to the surface and then farther out. But, in fact,
the temperature rises sharply in the Sun's atmosphere, called the corona. And
the same is true of other stars.
Weird, because there is a law that says this can't be so.
"The second law of thermodynamics says that temperature can only drop
when you move away from the heat source," says Markus Aschwanden, a solar
researcher at the Lockheed Martin Solar and Astrophysics Laboratory. "So
there is something magic and invisible that heats the solar and stellar
coronae."
After many decades of research into this weird thing, scientists are
only beginning to understand what might be going on.
Return
to the Main Weird Page
|
Weird Fact
Sunlight takes about 8 minutes to reach Earth. So when you
look at a tree, you're seeing it with light from the past.
|
More About The Sun's Hot Atmosphere
Aschwanden points out that the second law of thermodynamics works well
beyond the Sun's corona.
"The planets gets cooler and cooler when you travel outward in the
solar system," he points out. "Mercury is boiling hot, and Pluto is just arctic cold."
And it works well in the middle of the Sun.
"The hottest place is in the center of the Sun, maintained at a
cozy 15 million degrees Celsius (27 million Fahrenheit) by the nuclear
reactions that burn hydrogen to helium," Aschwanden says. "The
temperature drops steadily from the solar core to the surface, down to 5,000
degrees (9,000 Fahrenheit) at the surface."
But why does this temperature suddenly rise to around 2 million degrees
Celsius (3.6 million Fahrenheit) in the corona?
Recent data collected by Sun-observing spacecraft hint at an answer, he says. Giant magnetic
loops of energy
leap above the surface and may heat up dense clouds of matter called plasma.
This heated plasma then continues flowing upward, warming the corona.
He said the explanation is not proven. A deeper understanding of plasma
physics and more observations will be needed to solve the puzzle of the hot
atmosphere of our Sun and other stars.
Return
to the Main Weird Page . Next
Weird Thing
advertisement
LIVE
CAMS: 
