Tuesday, July 22, 2003

Moon May Outshine Meteor Shower

Moon May Outshine Meteor Shower
by Dave Adalian

Some say a full Moon is the most romantic nighttime sight. Others say it’s shooting stars. In mid-August we’ll get both on one night during the Perseids (per-SEE-ids), the year’s most reliable meteor shower.

Falling stars aren’t really stars. Your run-of-the-mill meteor is caused by a tiny piece of rock--a meteoroid--the size of a grain of sand with the consistency of ash. They vaporize high in the atmosphere as friction from their tremendous speed causes them and the air around them glow briefly and brightly.

Most of the time they arrive sporadically, a couple every hour more or less. Periodically the rates climb, putting on a spectacular show if conditions are right.

The random bits of debris are crumbs from ancient collisions among comets and asteroids. Left floating for billions of years, the pieces sometimes fall to Earth in blazing glory one at a time.
Meteor showers, however, are caused by Earth crossing the path of a large comet or asteroid. As these bodies loop around the Sun, they lose pieces of themselves which slowly drift ahead and behind until they spread throughout their parent’s orbit.

When Earth enters one of these streams and turns its night side toward the onrushing meteoroids, the fireworks begin.

On the night of August 12, we’ll be in the thickest part of the trail left by Comet Swift-Tuttle. When this happens, rates usually climb to 80 meteors or more an hour. In 1993, hourly rates at the peak were estimated at 200 to 500.

Unfortunately, August 12 is also the night of full Moon and our bright neighbor will outshine most of the show.

It’s still worth going out for a look. The Moon will be low when the shower peaks near 10 o’clock, so from a dark site we might see 20 to 40 meteors or more an hour. Or perhaps less or even none--meteor shower prediction is still a science in its infancy. But, surprises do happen.
To view the shower, set up a low-slung chair or lounge with your head pointing northwest--the opposite direction from a close pairing of the rising full Moon and bright orange Mars--and watch the skies overhead.

The Perseids’ radiant, the area where the meteors seem to come from, lies north in the constellation Perseus. The shower lasts from July 23 to August 22, with slightly increased meteor activity before and after the peak.

Clear skies!


This column originally appeared in the Visalia (Calif.) Times-Delta on July 22, 2003.

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