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.
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.
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!
advertisement
