By Kaylee Brewsterkbrewster@lmtribune.com
If you’re seeing stars falling from the sky this weekend, don’t worry — it’s just the Perseids meteor shower.
The Perseids shower (pronounced PER-see-ids) is so named because it appears to be moving away from the Perseus constellation, located west of Andromeda.
According to Jason Barnes, associate professor of physics at the University of Idaho, meteors or “shooting stars” are little bits of interplanetary dust that collide with Earth. For ordinary meteors, the collision is at a high rate of speed: about 19 miles per second.
“At that speed you could get from Moscow, Idaho, to Lewiston, Idaho, in two seconds,” Barnes said. “Much faster than driving.”
When these dust particles hit the Earth’s atmosphere at that speed, there is air resistance. The friction causes the particles to slow down and heats them up to glowing-hot temperatures, making them visible from Earth’s upper atmosphere even though they are only the size of a grain of sand.
The Perseids are so prominent because they move even faster than typical meteors, entering Earth’s atmosphere at around 36 miles per second.
“It’s more like a head-on collision because the comet is orbiting somewhat backwards,” Barnes said.
The Perseids meteor shower occurs in mid-August every year, when the Earth moves through a particular part of its orbit around the sun, leading us right across the orbit of Swift-Tuttle, Barnes said. He describes the comet as “a dirty snowball” about 16 miles across.
The dust that forms the meteor show, according to Matt Hedman, assistant professor of physics at the University of Idaho, is from the tail of Swift-Tuttle. The dust is launched into space as the comet slowly circles the sun and its ice is vaporized.
“Every time the Earth gets close to Swift-Tuttle’s orbit,” Hedman said, “it plows through this dust cloud, and the dust particles it encounters do completely burn up in our atmosphere.”
The Perseids shower also is known for its fireballs, which are superbright meteors lasting for several seconds, formed by a “big” piece of comet about the size of a grape. “Unlike the smaller sand-sized ones, you can frequently see some color in them, and they will sometimes start to get broken apart by the friction with the air, leading to them shooting parts off or exploding like a firework,” said Barnes. “They’re rare but super impressive if you get to see one.”
Barnes and Hedman recommend a dark, clear view of the sky, far from buildings and preferably on a hill, to view the Perseids meteor shower. It’s most easily seen after midnight and before dawn. Hedman’s advice is to bring a deck chair and let your eyes adjust to the dark.
Scientists are predicting a show of around 60 meteors per hour this year, one per minute.
“Your eye is great at seeing motion and should pick up meteors across most of the sky this way,” Barnes said. “They only last for about one second for most of them. I’ve found that it’s useless to point them out to your companions as by the time you blurt it out, the thing’s already gone. But hopefully they were looking up too and saw the same one that you did.”
Barnes and Hedman say earthlings should not be concerned about pieces of rock falling from the sky.
“They’re slowed down to terminal velocity in the upper atmosphere,” Barnes said. “So by the time that they get down here, they’re just falling little pieces of sand and will pose no threat to anyone or anything down here on the surface of Earth.”