Mercury,
Venus and Saturn are converging for a spectacular close encounter
this weekend.
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June 22, 2005: Stick up your thumb and hold it at
arm's length. It doesn't seem very big, does it? But it is,
big enough to hide three planets.
This
weekend Mercury, Venus and Saturn are going to crowd together
in a patch of sky no bigger than your thumb. Astronomers call
it a "conjunction" and it's going to be spectacular.
Right:
Saturn, Venus and Mercury converging at sunset on June 20,
2005. Image credit: Philip Downey of St. Catharines, Ontario.
The
show begins on Saturday evening, June 25th. Step outside and
look west toward the glow of the setting sun. Venus appears
first, a bright point of light not far above the horizon.
As the sky darkens, Saturn and Mercury pop into view. The
three planets form a eye-catching triangle about 1.5o
long, easily hidden by your thumb.
It gets better on Sunday evening, June 26th. The triangle shrinks
with Venus and Mercury only 0.5o apart. Now they
fit behind your pinky!
Monday
evening, June 27th, is best of all. With Saturn nearby, Venus
and Mercury converge. At closest approach, the two planets
will be less than one-tenth of a degree apart. Such pairings
of bright planets are literally spellbinding.
If
you go outside to see the show, take someone along. Here are
some fun facts you can share:
The
closest planet to the sun, Mercury, is not the hottest. Venus
is. The surface temperature of Venus is 870 F (740 K), hot
enough to melt lead. The planet's thick carbon dioxide atmosphere
traps solar heat, leading to a runaway greenhouse effect.
On Venus, global warming has run amok.
![see caption](images/spectacular/skymap_north_25jun05_strip.gif)
Above:
The western sky at sunset on Saturday, June 25th. More sky
maps: June
21, June
22, June
23, June
24, June
25, June
26, June
27, June
28.
Venus
is so bright because the planet's clouds are wonderful reflectors
of sunlight. Unlike clouds on Earth, which are made of water,
clouds on Venus are made of sulfuric acid. They float atop
an atmosphere where the pressure reaches 90 times the air
pressure on Earth. If you went to Venus, you'd be crushed,
smothered, dissolved and melted--not necessarily in that order.
Don't go.
Mercury
is only a little better. At noontime, the surface temperature
reaches 800 F (700 K). If you turn your kitchen's oven to
that setting, the pizza will burn to a smoking crisp. Radars
on Earth have pinged Mercury and found icy reflections near
the planet's poles. How can ice exist in such heat? NASA's
MESSENGER spacecraft is en route to Mercury now to investigate.
Here's
one way to trick an astronomer: Show them a picture of Mercury
and ask what it is. Many will answer "the Moon,"
because the Moon and Mercury look so much alike. But Mercury
has something that the Moon does not: long sinuous cliffs
called "lobate scarps." Some researchers think Mercury's
scarps are like wrinkles in a raisin, a sign of shrinkage.
A shrinking planet? Weird.
Right:
A lobate scarp on Mercury, photographed by Mariner 10 in 1974.
[More]
If
you look at Venus or Mercury through a telescope, you won't
be impressed. Both are featureless, Venus because of its bland
clouds, Mercury because it is small and far away. Saturn is
different. Even a small telescope will show you Saturn's breathtaking
rings.
Galileo
Galilei discovered Saturn's rings almost 400 years ago, but
he didn't understand what he saw. A planet with rings was
too much even for Galileo. Scientists today are still reeling.
Saturn's rings are improbably thin. If you made a 1-meter-wide
scale model of Saturn, the rings would be 10,000 times thinner
than a razor blade. They're full of strange waves and spokes
and grooves. And no one knows where they came from.
One
school of thought holds that Saturn's rings are debris from
the breakup of a tiny moon or asteroid only a few hundred
million years ago. As recently as the Age of Dinosaurs on
Earth, Saturn might have been a naked planet--no rings! Tiny
moons orbiting among the rings today appear to be stealing
angular momentum, which, given time, could cause the rings
to collapse. Is Saturn like a flower, temporarily in bloom?
![see caption](images/spectacular/saturnplane_cassini_strip2.jpg)
Above:
Saturn's rings viewed edge-on. Photo credit: Cassini. [More]
That's
one of many questions being investigated by NASA's Cassini
spacecraft, which has been orbiting Saturn since 2004. Cassini
is on a 4-year mission to study Saturn's moons (all 34 of
them), rings and weather. Every day the craft beams stunning
images to Earth: click
here to see them.
A
lot can happen behind your thumb. This weekend is a good time
to look.
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Author: Dr. Tony
Phillips | Production
Editor: Dr. Tony
Phillips | Credit: Science@NASA
More
Information |
An
Absolutely Spectacular Super Close Meeting of Three
Planets Occurs This Week and Next -- from Jack Stargazer
Sky
maps: June
21, June
22, June
23, June
24, June
25, June
26, June
27, June
28.
Spaceweather.com
-- check this site in the days ahead for pictures of
the conjunction
The
Real Lord of the Rings -- (Science@NASA) Four hundred
years after they were discovered, Saturn's rings remain
a mystery.
MESSENGER
-- NASA's mission to Mercury
Mysteries
of Mercury -- from the MESSENGER team
Cassini
-- Get the latest news, beamed directly from Saturn.
Planet
facts: Mercury,
Venus
and Saturn. |
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