The Oregon Museum of Science and Industry (OMSI) is getting ready for its largest star party of the year on Friday, August 12, the Perseid Meteor Shower Watch! Hundreds of star lovers from across the Pacific Northwest will be meeting at both Rooster Rock State Park and Stub Stewart State Park at 9 p.m. to watch and enjoy the wonder of the Perseid Meteor Shower. The event, sponsored by OMSI, the Rose City Astronomers, the Vancouver Sidewalk Astronomers and Oregon Parks and Recreations will have telescopes set up for attendees to use. OMSI staff will be presenting informal talks about the meteor shower, constellations, and the summer sky.
The Perseid Meteor Shower occurs when the Earth enters the path of debris left by the comet Swift-Tuttle in its last trip past the Sun. Swift-Tuttle follows a highly eccentric orbit around the Sun with an orbital period of about 130 years. The comet last passed by the Earth in December 1992. Timing is not precise, but according to the American Meteor Society, the 2011 peak is expected on August 12th at around 9:00 p.m. PDT (0400 hours UT on August 13). There is some uncertainty, so it’s very worthwhile to observe on either side of this time. The OMSI Star Parties will be held on the night of August 12 and into the early morning of August 13. Estimate peak rates for this year’s Perseid is near 60 for those under transparent rural skies. Those under dark but hazy skies should still be able to see 30 to 40 Perseids per hour. Those under urban skies will be lucky to exceed 10 to 20 per hour. Unfortunately, this year will have the full moon on August 12 and will be a factor for viewing the fainter meteors of the Perseids. While viewing the Perseids, we will look at the Moon, Saturn and later Jupiter. As a bonus, the International Space Station will be visible on the same night.
To reach Rooster Rock State Park, take I-84 east of the Sandy River at exit 25. The park is located 22 miles east of Portland. To reach L.L. “Stub” Stewart State Park, take US-26 west of Portland and turn right on OR-47. The park is located 23 miles west of Portland. The event is free, and there is a $5 per vehicle parking fee for public. For possible weather cancellation, call (503) 797-4610 on August 12 after 4:00 PM to get the latest information.
An increase in the number of meteors at a particular time of year is called a meteor shower. Comets shed the debris that becomes most meteor showers. As comets orbit the Sun, they shed an icy, dusty debris stream along the comet’s orbit. If Earth travels through this stream, we will see a meteor shower. Depending on where Earth and the stream meet, meteors appear to fall from a particular place in the sky, maybe within the neighborhood of a constellation.
Meteor showers are named by the constellation from which meteors appear to fall, a spot in the sky astronomers call the radiant. For instance, the radiant for the Leonid meteor shower is located in the constellation Leo. This meteor shower gets the name “Perseids” because it appears to radiate from the constellation Perseus. An observer in the Northern Hemisphere can start seeing Perseid meteors as early as July 23, when one meteor every hour or so could be visible. During the next three weeks, there is a slow build-up. It is possible to spot five Perseids per hour at the beginning of August and perhaps 15 per hour by August 10. The Perseids rapidly increase to a peak of 50-80 meteors per hour by the night of August 12/13 and then rapidly decline to about 10 per hour by August 15. The last night meteors are likely to be seen from this meteor shower is August 22, when an observer might see a Perseid every hour or so.
“Shooting stars” are intense streaks of light across the night sky caused by small bits of interplanetary rock and debris called meteoroids crashing and burning high in Earth’s upper atmosphere. Traveling at thousands of miles an hour, meteoroids quickly ignite in searing friction of the atmosphere, 30 to 80 miles above the ground. Almost all are destroyed in this process; the rare few that survive and hit the ground are known as meteorites.
Most people do not know how easy it is to watch a meteor shower. Although it is Summer, evening temperatures can drop and jackets may be a necessity. Choose an observing location giving a wide view of the sky with as few obstructions as possible. If you’re viewing from the city, try to observe where artificial lights interfere the least. Places like Rooster Rock State Park, Mt Hood area, or eastern Oregon are popular locations for dark sky in viewing the meteor shower. Possible to watch it from the comfort of your backyard, but only the bright meteors would be visible. Meteor watching is basically an unaided-eye event but binoculars are handy for watching trails (persistent trains) that may hang in the sky for one or more seconds after a meteor’s passage.
The Radiant will be low in the northeast sky after sunset. For early evening viewing, be outside about the time the first stars appear. The Radiant will be low in the northeast but don’t concentrate just on that one area, but rather, let your gaze wander over a large portion of the sky. Meteors that appear near the Radiant will have short paths while those that begin farther out have much longer ones. In the early evening you may spot a few so-called Earth Grazers which can blaze long trails across the sky. They’re not likely to be numerous but do appear, sometimes at the rate of half a dozen or more an hour.
As the hours pass the Radiant rises higher and between about midnight and dawn the greatest number of meteors can be seen. Viewing through city lights will reduce their numbers considerably but the brighter ones will show up nicely.