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April
17, 2009: Picture this: It's 4:30 in the morning.
You're up and out before the sun. Steam rises from your coffee
cup, floating up to the sky where a silent meteor streaks
through a crowd of stars. A few minutes later it happens again,
and again. A meteor shower is underway.
One
of the streaks leads to the eastern horizon. There, just above
the tree line, Venus and the crescent Moon hover side by side,
so close together they almost seem to touch. Suddenly, Venus
wavers, winks, and disappears.
All
of this is about to happen--for real.
Right:
A Venus-Moon conjunction photographed Monika Landy-Gyebnar
of Balatonakarattya, Hungary, on Dec. 1, 2008. [Larger
image]
On
Wednesday morning, April 22nd, Earth will pass through a stream
of comet dust, giving rise to the annual Lyrid meteor shower.
At the same time, the crescent Moon and Venus will converge
for a close encounter in the eastern sky. Viewed from some
parts of the world, the Moon will pass directly in front of
Venus, causing Venus to vanish.
The
source of the meteor shower is Comet Thatcher. Every year in
late April, Earth passes through the comet's trail of debris.
Flakes of comet dust, most no bigger than grains of sand, strike
Earth's atmosphere traveling 110,000 mph and disintegrate as
fast streaks of light. A typical Lyrid shower produces 10 to
20 meteors per hour over the northern hemisphere, not an intense
display. Occasionally, however, Earth passes through a dense
region of the comet's tail and rates increase five- to ten-fold.
In 1982, observers counted 90 Lyrids per hour. Because Thatcher's
tail has never been mapped in detail, the outbursts are unpredictable
and could happen again at any time. The probabilities are highest
during the dark hours before sunrise on April 22nd.
The
Moon-Venus conjunction is pure coincidence. It has nothing
to do with the Lyrid display other than insurance. Even if
the shower fizzles, the sight of a 9% crescent Moon located
so close to brilliant Venus is guaranteed to make your day.
Most
observers will see only a close gathering of the two bodies.
People in western parts of North America are favored with
more--a full-blown eclipse or "occultation." Around
5 a.m. Pacific Daylight Time, Venus will disappear behind
the mountainous rim of the Moon and reappear 60 to 90 minutes
later. Click on the map for local details:
Above:
Visibility diagrams for the April 22, 2009, lunar occultation
of Venus. In the map, times are given in UT. Subtract 7 hours
to obtain PDT. Credit: Sky & Telescope. Copyright 2009,
all rights reserved. [more]
Do
not worry if the sun rises during the occultation, because
Venus and the Moon are bright enough to see in broad daylight.
Locate the pair before sunrise, so you know where they are,
then follow them up the brightening sky using binoculars or
naked eyes. Some people say Venus and the Moon are most beautiful
when surrounded by morning blue.
On
Wednesday morning, April 22nd, you can see for yourself.
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Author: Dr.
Tony Phillips | Credit: Science@NASA
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