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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 Highnesses…." 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.
Right:
Cassini's view of Saturn's blue north: full
story.
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 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.
Above:
Saturn's rings are wide but very thin. Astronomers using the
Hubble Space Telescope captured this image of the rings edge-on
in 1995. Star-like objects in the ring plane are icy satellites.
[more]
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), and Wednesday, March 19th (sky
map), 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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Author: Dr.
Tony Phillips | Credit: Science@NASA
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