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Dec.
22, 2008: You look through the telescope. Blink.
Shake your head and look again. The planet you expected to
see in the eyepiece is not the one that's actually there.
Too much eggnog?
No,
it's just Saturn's crazy Christmas tilt.
All
year long, the rings of Saturn have been tilting toward Earth
and now they are almost perfectly edge-on. The opening angle
is a paper-thin 0.8o. Viewed from the side, the
normally wide and bright rings have become a shadowy line
bisecting Saturn's two hemispheres--a scene of rare beauty.
Amateur
astronomer Efrain Morales Rivera of Aguadilla, Puerto Rico,
has been monitoring Saturn and he created this composite image
to show how the geometry has changed:
Astronomers
call the phenomenon a "ring plane crossing." As
Saturn goes around the sun, it periodically (once every 14
to 15 years) turns its rings edge-on to Earth. Because the
rings are so thin, they can actually disappear when viewed
through a backyard telescope. At the precise moment of crossing,
Saturn undergoes a startling metamorphosis. The ringed planet
becomes a lonely ball of gas, almost unrecognizable: Hubble
photo.
(Historical
note: Shortly after Galileo discovered Saturn's rings in 1610,
they disappeared in precisely this fashion. Galileo didn't
understand the nature of the rings and the vanishing act confused
him mightily. Nevertheless, his physical intuition prevailed.
"They'll be back," he predicted, and without ever
knowing why, he was correct.)
We're
not quite there yet. The opening angle won't be precisely 0o
until Sept. 4, 2009. Don't bother marking your calendar, though.
Saturn will be so close to the sun, no one will be able to see
the rings wink out.
The
best time to look is now.
The
0.8o opening angle of Christmas 2008 is the minimum
for some time to come. In January 2009 the rings begin to
open up again, a temporary reversal caused by the orbital
motions of Earth and Saturn. By the time narrowing resumes
in summer 2009, Saturn will be approaching the sun; looking
through a telescope then could actually be dangerous. The
next ring plane crossing that's easy to watch won't come until
2038.
So
wake up before sunrise on Dec. 25th, point your telescope
at the golden "star" in Leo, and behold Saturn's
crazy Christmas tilt: sky
map.
Happy
holidays from Science@NASA!
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Author: Dr.
Tony Phillips | Credit: Science@NASA
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