July 31, 2009
The Perseids Are Coming
Earth is entering a stream of dusty debris from Comet Swift-Tuttle, the source of the annual Perseid meteor shower. Although the shower won't peak until August 11th and 12th, the show is already getting underway.
Don't get too excited, cautions Bill Cooke of NASA's Meteoroid Environment Office. "We're just in the outskirts of the debris stream now. If you go out at night and stare at the sky, you'll probably only see a few Perseids per hour."This will change, however, as August unfolds.
"Earth passes through the densest part of the debris stream sometime on August 12th. Then, you could see dozens of meteors per hour."
For sky watchers in North America, the watch begins after nightfall on August 11th and continues until sunrise on the 12th. Veteran observers suggest the following strategy: Unfold a blanket on a flat patch of ground. (Note: The middle of your street is not a good choice.) Lie down and look up. Perseids can appear in any part of the sky, their tails all pointing back to the shower's radiant in the constellation Perseus. Get away from city lights if you can.
There is one light you cannot escape on August 12th. The 55% gibbous Moon will glare down from the constellation Aries just next door to the shower's radiant in Perseus. The Moon is beautiful, but don't stare at it. Bright moonlight ruins night vision and it will wipe out any faint Perseids in that part of the sky.
The Moon is least troublesome during the early evening hours of August 11th. Around 9 to 11 p.m. local time (your local time), both Perseus and the Moon will be hanging low in the north. This low profile reduces lunar glare while positioning the shower's radiant for a nice display of Earthgrazers.
"Earthgrazers are meteors that approach from the horizon and skim the atmosphere overhead like a stone skipping across the surface of a pond," explains Cooke. "They are long, slow and colorful"”among the most beautiful of meteors." He notes that an hour of watching may net only a few of these at most, but seeing even one can make the whole night worthwhile.
The Perseids are coming. Enjoy the show.
By Dr. Tony Phillips, Science @ NASA
Image 1: Brian Emfinger of Ozark, Arkansas, photographed this early Perseid just after midnight on Sunday, July 26th. "I used an off-the-shelf digital camera to capture this fireball and its smoky trail," says Emfinger. "It was a bright one!" he said.
Image 2: Looking northeast around midnight on August 11th-12th. The red dot is the Perseid radiant. Although Perseid meteors can appear in any part of the sky, all of their tails will point back to the radiant. Image copyright: Spaceweather.com, used with permission.
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