Apr. 21, 1999:
Stargazers in recent months may have noticed something
missing from the
nighttime sky: shooting stars. Each year between January and April
there is a lull in meteor activity as Earth passes through a part of
its orbit that is free from major cometary debris streams.
Without much space dust in the area, there are simply fewer cosmic
particles burning up in the atmosphere to produce visible
shooting stars.
Above: Artist Duane Hilton created this
nighttime painting of a Lyrid meteor streaking over sand dunes in Death Valley, CA.
It's been a long 3 months for meteor enthusiasts, but the
1999 intermission in meteor activity is
nearly over. It ends this
Thursday with the arrival of the annual Lyrid meteor shower.
The Lyrids will peak at
1600 UT (9 a.m. Pacific Standard Time)
on April 22
with at least 10-20 meteors
per hour. The predicted peak occurs during daylight on Thursday morning
across most of the United States, but the rate of meteors
should still be high
a few hours earlier before the sun rises.
No matter where you live, the best time to look will be
during the hours before dawn
on Thursday after the waxing quarter Moon has set.
Typical Lyrid meteors are nearly as bright as
the main stars in the Big Dipper, which makes it a
good shower for both beginning and experienced observers.
Most years, observers of the Lyrids
can
expect to view one or two
shooting stars every few minutes. That's just a trickle
compared to the avalanche of shooting stars and fireballs
seen by millions during the 1998 Leonids meteor shower, but
the Lyrids are not always so meek. In 1982, for example, over 90 meteors per hour were
seen for a brief time. An even bigger outburst in 1803
was documented by a journalist in Richmond, Virginia who wrote:
"Shooting stars. This electrical phenomenon was
observed on Wednesday morning last at Richmond and its vicinity, in a manner that alarmed many, and
astonished every person that beheld it. From one until three in the morning, those starry meteors seemed
to fall from every point in the heavens, in such numbers as to resemble a shower of sky rockets..." [ref]
Another account quoted an observer who
"counted 167 meteors in about 15 minutes, and
could not then number them all." [ref]
Although the Lyrids are not usually so spectacular,
they are notable as the oldest recorded meteor
shower. Lyrids have been observed for at least 2600 years, according
to Chinese records from 687 BC describing "stars that fell [like]
rain."
The Lyrid meteor stream is asscociated with periodic
comet Thatcher C/1861 G1, whose
orbit is tilted nearly 80 degrees with respect to
the plane of the solar system. Because the comet spends most of its
time well away from the planets, it is nearly immune to significant
gravitational perturbations. This is probably the
reason why the debris stream has remained stable and the
Lyrid shower has been observed for so many centuries.
How to View the Lyrids
Lyrid meteors can be seen anytime after midnight
when the constellation Lyra is well above the horizon. The
best time to look is between
about 3 a.m. and dawn. That's when the local sky is pointing
directly into the meteoroid debris stream (see the diagram below).
The early morning hours of April 23 and April 24 should be good times to watch no matter where you live.
Above:The rate of meteor activity
is usually greatest near dawn because the earth's orbital motion is in
the direction of the dawn terminator. Earth scoops up meteoroids
on the dawn side of the planet and outruns them on the dusk side.
Lyrids
at a Glance
- The meteor shower
is active from Apr. 16 until April 25.
- Maximum activity is expected at 1600 UT on Apr 22, 1999.
- The radiant is at
RA=18h06m, DEC=+33o
- Atmospheric velocity=49 km/s
- Average magnitude 2.4
Current Moon Phase
Updated every 4 hours.
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The constellation Lyra, pictured in the sky map below,
rises at approximately 11:00 p.m. local time at mid-latitudes in
the Northern hemisphere. The radiant of the shower is
located near Vega, a hard-to-miss zeroth magnitude star.
Vega is well-known as a member of the "Summer Triangle" of
bright stars which also includes Deneb and Altair.
To find Lyra at 2:00
a.m., go outside and face north-northeast.
Vega will appear
approximately 50 degrees above the horizon between the
constellations Cygnus and Hercules.
You won't need binoculars or a telescope to observe Lyrid meteors,
the naked eye is usually
best for seeing meteors which often streak more than 45 degrees
across the sky. The field of view of most binoculars and telescopes
is simply too narrow for good meteor observations.
Experienced observers suggest the following viewing strategy:
Dress warmly. Bring
a reclining chair, or spread a thick blanket over a flat spot
of ground. Lie down and look up somewhat toward the north. Meteors
can appear in any part of the sky, although their trails will
tend to point back toward the radiant, pictured in the sky map below)
The image indicates the
general region of the sky from which the Lyrid meteors appear
to emanate (red dot). This point, called the radiant, is really
an optical illusion - the meteors are moving along parallel paths,
but appear to come from a single point, just as a stretch of
parallel railroad tracks will appear to meet at a point on the
horizon.
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