Moonlit Meteors
April
18, 2000: April showers are supposed to bring May flowers,
according to the well-known school yard rhyme. But there's a
shower coming up this April that won't advance the cause of Spring
one bit -- it's the Lyrid meteor shower. While the Lyrids may
not encourage flowers to bloom, there will be a modest sky show
on the morning of April 22 when 10 to 15 meteors per hour shoot
out of the constellation Lyra.
Above: Artist Duane
Hilton created this rendition of a Lyrid meteor streaking
past the Moon over the Sawtooth Ridge near Mammoth, CA.
"Unfortunately there's going to be a nearly full moon this
year on April 22nd," said Dr. Frank Six, an astronomer at
the NASA Marshall Space Flight Center. "That'll make it
hard to see faint meteors. Still, it might be worth staying up
for if you're an enthusiastic star gazer." [click
here for observing tips]
All meteor showers are caused by dust particles from comets.
The comet itself doesn't need to be anywhere nearby. These occasional
icy visitors to the inner solar system leave a long trail of
debris behind as they pass by the Sun. If our planet happens
to pass through one of these debris streams, tiny dust particles
called meteoroids burn up in our atmosphere producing a streak
of light. All of the well-known annual meteor showers, like the
Leonids and Perseids, as well as the Lyrids, are associated with
long-lasting cometary debris streams that intersect Earth's orbit.
Left:
Meteors are caused by tiny dust particles called meteoroids that
burn up in Earth's atmosphere. What does a meteoroid look like?
This picture shows a tiny meteoroid that was captured high in
the stratosphere before it burned up or hit the ground. This
one is only 10 microns across! [more
information from JPL]
Most meteoroids are tiny and insubstantial -- usually no bigger
than grains of sand and much less dense -- but they move very
fast. Lyrid meteoroids, for example, blaze through the atmosphere
faster than 109,000 mph (49 km/s). The high speed is what allows
these diminutive specks of dust to produce such bright meteors.
Typical Lyrid meteors are nearly as bright as the main stars
in the Big Dipper, which makes the shower a good one 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 skywatchers
during last year's Leonids
meteor storm, 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]
While intense Lyrid displays are not unheard of, they are rare. In fact, the Lyrids are better known for their longevity than for their dazzle. Lyrids have been observed for at least 2600 years, according to Chinese records from 687 BC describing "stars that fell [like] rain." This makes it the oldest recorded meteor shower.
The Lyrid meteor stream is associated with periodic comet Thatcher, which follows an orbit 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 from 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.
The early morning hours of April 22, between 3 a.m. and dawn, are the best times to watch for Lyrid meteors no matter where you live. The shower's peak is expected sometime between 22h UT on the 21st and 05h UT on the 22nd. Some activity from this shower can be seen from about April 16th to 25th, but the rates will be much lower away from the peak.
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 zero-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 3:00 a.m., go outside and face north-northeast. Vega will appear approximately 60 degrees above the horizon between the constellations Cygnus and Hercules.
Above: This image shows 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.
You won't need binoculars or a telescope to observe Lyrid
meteors; the naked eye is usually best for seeing shooting stars,
which often streak more than 20 degrees across the sky. The field
of view of most binoculars and telescopes is simply too narrow
for casual 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)
Lyrids at a Glance |
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.
Web LinksThe Lyrids - From Gary Kronk's Comets & Meteors Web Site
North American Meteor Network - April 2000 Newsletter featuring information about the Lyrids
North American Meteor Network - home page