Perseids to Storm August 11?
|Observing Perseids on August 11. Meteor showers producing up to 100 per hour have seasons and are named after the background constellations: April and June = Lyrids, August = Perseids, October = Orionids, November = Taurids, Leonids.
Credit: S&T Mag.
The Perseid meteor shower, an annual celestial event beloved by millions of skywatchers around the world, returns to the night sky this week near the North Star and the constellation Perseus.
Sky & Telescope magazine predicts that the Perseid shower will reach its peak late Wednesday night and early Thursday morning, August 11-12. The rate of activity should pick up steam after midnight until the first light of dawn. North America, especially the West and Hawaii, is optimally positioned to catch the best of the shower.
An observer under a dark sky might typically see more than 60 Perseids per hour between midnight and dawn. Since the waning crescent Moon will be only three days from new at the time of shower maximum, posing minimal interference with the view, this is an opportune year for watching them.
You’ll need no equipment but your eyes. The darker your sky, the better any artificial light pollution in your sky will reduce the number of meteors that are visible. But even if you live in an urban or suburban area, you have a good chance of seeing at least some meteors. Find a dark spot with a wide-open view of the sky. Bring a reclining lawn chair, insect repellent, and blankets or a sleeping bag; clear August nights can get surprisingly chilly.
"Go out after about 11 p.m. or so, lie back, and watch the stars," says Sky & Telescope senior editor Alan MacRobert. "Relax, be patient, and let your eyes adapt to the dark. With a little luck you’ll see a ‘shooting star’ every couple of minutes on average."
Perseids can appear anywhere and everywhere in the sky. So the best direction to watch is wherever your sky is darkest, probably straight up. Faint Perseids appear as tiny, quick streaks. Occasional brighter ones may sail across the heavens for several seconds and leave a brief train of glowing smoke.
|A composite of Leonid meteor images recorded by a CCD camera onboard the MSX satellite|
If you trace each meteor’s direction of flight backward far enough across the sky, you’ll find that your imaginary line crosses a spot in the constellation Perseus, near Cassiopeia. This is the shower’s radiant, the perspective point from which all the Perseids would appear to come if you could see them approaching from interplanetary space. The radiant is low in the north-northeast before midnight and rises higher in the northeast during the early-morning hours.
Don’t give up if it’s cloudy Wednesday night. The Perseid shower lasts for about two weeks, with good rates in the predawn hours of August 10th through 15th. This year the ever-thinning Moon becomes less of a problem with each passing night. Far fewer meteors will appear before midnight, even on the night of the shower’s maximum, because the radiant is then quite low in the sky. The radiant is always low or below the horizon for Southern Hemisphere countries like Australia, New Zealand, and South Africa, where few, if any, Perseids can be seen.
The Perseid meteoroids are tiny, sand- to pea-size bits of rocky debris that were shed long ago by Comet Swift-Tuttle. This comet, like others, is slowly disintegrating as it orbits the Sun. Over the centuries, its crumbly remains have spread all along its 130-year orbit to form a sparse "river of rubble" hundreds of millions of miles long.
Earth’s own path around the Sun carries us through this stream of particles every mid-August. The particles, or meteoroids, are traveling 37 miles per second with respect to Earth at the place where we encounter them. So when one of them strikes the upper atmosphere (about 50 to 80 miles up), it creates a quick, white-hot streak of superheated air.
For several years in the early 1990s the Perseids performed spectacularly, flaring with outbursts of up to hundreds of meteors per hour. The particles responsible for these outbursts were probably shed during Comet Swift-Tuttle’s swing by the Sun in 1862.
Astronomers Esko Lyytinen of Finland and Tom Van Flandern of Washington, DC, have alerted skygazers to the possibility that this "extra" Perseid peak could make a comeback in 2004. They predict that this year, the rubble trail released in 1862 will pass just 200,000 kilometers (125,000 miles)) inside Earth’s orbit on August 11th, just as observing conditions become optimal for meteor watchers in Eastern Europe and eastern North Africa eastward to central Russia, India, and western China.
Will the Perseids "storm" in 2004? There’s only one way to find out: Get outside and watch the show!