|
+ Play Audio |
+ Download Audio | +
Historia en Español | +
Email to a friend | + Join mailing list
March 6, 2006: Every year in February, the students
of Mrs. Phillips's 5th grade class in Bishop, California,
celebrate Galileo's birthday (Feb. 15th) by repeating one
of his discoveries. They prove that the sun spins.
It's
simple. Step 1: Look at the sun. Galileo did this using a
primitive telescope; Mrs. Phillips's students use the internet.
Step 2: Sketch the sunspots. Step 3: Repeat daily. After only
a few days, it's obvious that the sunspots are moving and
sun is spinning, performing one complete turn every 27 days.
 This
procedure worked fine in 1610. But in 2006, "we had a
problem," says young Jonathan Garcia. "No sunspots,"
explains his science fair partner Dakota Winkler.
Right:
A picture of the sun taken Feb. 10, 2006, by the Solar and
Heliospheric Observatory (SOHO). [Larger
image]
For
almost the entire month of February 2006 the sun was utterly
blank. If Galileo had looked at the sun on his 442nd
birthday, he would have been disappointed—no sunspots, no
spin, no discovery.
What's
going on? NASA solar physicist David Hathaway explains: "Solar
minimum has arrived."
Sunspots
come and go with an 11-year rhythm called the sunspot cycle.
At the cycle's peak, solar maximum, the sun is continually
peppered with spots, some as big as the planet Jupiter. But
for every peak there is a valley, and during solar minimum
months can go by without a single sunspot.
"That's
where we are now—at minimum," says Hathaway.
Actually,
we're at the beginning of the minimum. February 2006 was the
first month in almost ten years with mostly no sunspots. For
21 of February's 28 days, the sun was blank. Hathaway expects
this situation to continue for the rest of 2006.
Below:
Sunspot counts from the time of Galileo through the end of
2005. In recent centuries, counts have gone up and down with
an 11-year period. [More]
No
sunspots means low solar activity. Sunspots are sources of
solar flares and coronal mass ejections that can disrupt radio
communications and even cause power outages on Earth during
severe magnetic storms. These problems should subside during
the year ahead. Auroras, a beautiful side-effect of magnetic
storms, should subside, too. "Too bad," says Hathaway,
who enjoys Northern Lights.
Galileo
was lucky. The year 1610 was close to a maximum of the sunspot
cycle, so when he projected an image of the sun through his
spyglass, he immediately saw enormous spots. The spots themselves
did not surprise him. Chinese astronomers looking at the sun
naked-eye through clouds and mist had reported seeing sunspots
as early as 28 BC. The reality of sunspots was uncontroversial,
but the nature of sunspots was a mystery. Were they satellites
of the sun? Dark clouds in the sun's atmosphere? Or something
else? Galileo's daily sketches showed plainly that the sun
was spinning and that sunspots were close to the surface of
the spinning orb. Personally, Galileo thought sunspots might
be clouds.
 Right:
A sketch of the sun made by Galileo in June 1613. [More]
Now
we know what they really are: great islands of magnetism.
Sunspots appear when magnetic force-fields generated by the
sun's inner dynamo poke through the surface. These fields
block the flow of heat from below, cooling the sun in their
vicinity. If you stuck a thermometer in a sunspot, it would
register "only" a few thousand degrees Celsius.
This makes it look dark compared to the surrounding inferno.
Sunspots
are in a state of non-stop upheaval. Tangled lines of magnetism
twist and stretch until the tension becomes too great and
an explosion occurs—a flare. This link between flares and
spots is why solar minimum is so quiet.
"But
not absolutely quiet," adds Hathaway. "During solar
minimum we can have occasional sunspots and solar
flares." Indeed there was at least one monster spot and
one X-class solar flare (the most powerful kind) during each
of the last three minima in 1976, 1986 and 1996.
2006
will probably be the same—long stretches of quiet with occasional
episodes of spots and flares. How long will this last? Stay
tuned for the answer in our next story: "Solar Storm
Warning."
SEND
THIS STORY TO A FRIEND
Author: Dr. Tony
Phillips | Production Editor:
Dr. Tony Phillips | Credit: Science@NASA
|
