The Vanishing Rings of Saturn
- From: baalke@xxxxxxxxxxxxx
- Date: Fri, 28 Mar 2008 17:32:26 -0700 (PDT)
http://science.nasa.gov/headlines/y2008/18mar_saturn.htm
The Vanishing Rings of Saturn
NASA Science News
03.18.2008
March 18, 2008: Saturn: jewel of the solar system, taker of breaths,
ringed beauty. Even veteran astronomers can't help but gasp when they
see her through a small telescope.
Red Alert: Saturn's rings are vanishing.
Around the world, amateur astronomers have noticed the change;
Saturn's
wide open rings are rapidly narrowing into a thin line. Efrain Morales
Rivera sends these pictures taken through a backyard telescope in
Aguadilla, Puerto Rico:
"The rings have narrowed considerably in the last year," he reports.
"The Cassini division (a dark gap in the rings) is getting hard to
see."
Four hundred years ago, the same phenomenon puzzled Galileo. Peering
through a primitive spy glass, he discovered Saturn's rings in 1610
and
immediately wrote to his Medici patrons: "I found another very strange
wonder, which I should like to make known to their Highnessesâ¦." He
was
dumbfounded, however, when the rings winked out little more than a
year
later.
What happened?
The same thing that's happening now: we're experiencing a "ring plane
crossing." As Saturn goes around the sun, it periodically turns its
rings edge-on to Earth - once every 14-to-15 years. Because the rings
are
so thin, they can actually disappear when viewed through a small
telescope.
In the months ahead, Saturn's rings will become thinner and thinner
until, on Sept. 4, 2009, they vanish. When this happened to Galileo in
1612, he briefly abandoned his study of the planet. Big mistake: ring
plane crossings are good times to discover new Saturnian moons and
faint
outer rings.
It's also
a good time to behold Saturn's curiously blue north pole. In 2005 the
Cassini spacecraft flew over Saturn's northern hemisphere and found
the
skies there as azure as Earth itself. Saturn is a planet of golden
clouds, but for some reason clouds at high northern latitudes have
cleared, revealing a dome of surprising blue.
For years, only Cassini has enjoyed this view because from Earth, the
blue top of Saturn was hidden behind the rings. No more: "Now that
Saturn's rings are only open 8 degrees, we can finally view its
northern
hemisphere's beautiful teal blue colored belts and zones, which really
did look blue through my 10-inch telescope," reports Dan Petersen of
Racine, Wisconsin, who took this picture
<images/saturn/Dan-Petersen1.jpg> on Feb. 24, 2008.
Galileo never understood the true nature of Saturn's rings. He didn't
know that they were a disk-shaped swarm of orbiting moonlets ranging
in
size from microscopic dust to tumbling houses. (Scientists still
aren't
sure, but they may be debris from a shattered moon.) He didn't even
know
the rings were rings. Through his 17th-century telescope, they looked
more like ears or planetary lobes of some kind.
Yet, somehow, his intuition guided him to make a correct prediction:
"they'll be back," or Italian words to that effect. And he was right.
Saturn's rings opened up again and scientists resumed their study. In
1659, Christaan Huygens correctly explained the periodic
disappearances
as ring plane crossings. In 1660, Jean Chapelain argued that Saturn's
rings were not solid, but made instead of many small particles
independently orbiting Saturn. His correct suggestion was not widely
accepted for nearly two hundred years.
Almost 27 ring plane crossings later, we still marvel at Saturn. Even
with rings diminished, she is still a breathtaking sight through the
meanest of telescopes. Indeed, this is a good week to look. On
Tuesday,
March 18th (sky map <images/saturn/skymap_north_18mar08.gif>), and
Wednesday, March 19th (sky map
<images/saturn/skymap_north_19mar08.gif>), the nearly-full Moon and
Saturn will be lined up in the same part of the evening sky. That
makes
Saturn unusually easy to find: Go outside after sunset and look around
for the Moon; Saturn is the bright golden "star" nearby.
Point your telescope and, well, just try not to gasp.
Looking Ahead : If you miss the March 18-19 encounter, try again on
April 14-15. The Moon and Saturn will be close together and the rings
even narrower. Mark your calendar!
.
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