Spectacular Conjunction for Mercury, Venus and Saturn

http://science.nasa.gov/headlines/y2...pectacular.htm

Spectacular Conjunction
NASA Science News
June 22, 005

Mercury, Venus and Saturn are converging for a spectacular close
encounter this weekend.


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.

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 sha

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.

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.

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?

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
http://www.nasa.gov/mission_pages/cassini/main/index.html to see
them.

A lot can happen behind your thumb. This weekend is a good time to look.