Jimmy Westlake: October’s Orionid meteor shower
October 19, 2008
Did you get to see Halley’s Comet when it sailed past Earth in 1985-86? If not, you’ll have to wait until 2061 for another chance to see it, since Halley’s Comet requires 76 years to orbit the sun. In the meantime, you can watch tiny pieces of Halley’s Comet rain down into the Earth’s atmosphere every May and October, during the annual Aquarid and Orionid meteor showers.
Comets are like big, dirty snowballs, more than anything else, that hover near the outer edges of the solar system in perpetual cold and dark. But, every so often, the gravity of the sun pulls a comet into the warm inner regions of the solar system. As the snowball approaches the sun, the solar heat vaporizes the top layers of ice, releasing tons of steam and millions of tiny dust particles that were trapped in the ice. The forces of sunlight and the solar wind combine to blow the gaseous vapors away from the snowball, forming the comet’s beautiful, flowing tail and filling the comet’s path with dusty debris. The comet sheds millions of little dust specks each time it rounds the sun, leaving a river of dust in its wake.
The Earth crosses Halley’s dust river twice each year, once May 5 and again Oct. 21. When the dust particles plow into the Earth’s upper atmosphere at nearly 150,000 mph, they burn up in brief but brilliant flashes of light called meteors. The dust specks are so small that you could easily hold 1,000 of them in the cupped palm of your hand.
This year’s October Orionid meteor shower will peak in the wee hours between midnight and dawn Tuesday morning, Oct. 21. A single observer with dark, clear skies might see from 15 to 20 meteors, or, “shooting stars,” each hour. The third-quarter moon also shines near Orion on Oct. 21 this year, so it will interfere a little with meteor watching and wash out the faintest “shooting stars.”
The October meteors that Halley’s Comet sends our way seem to fan out from a point in the sky near the familiar star pattern of Orion the Hunter and are therefore called Orionid meteors. You’ll see the Orionid meteors in every part of the sky, but they will all trace back to a common origin near Orion’s bright star Betelgeuse, high in the southeastern sky, at about 4 a.m. The closer to dawn you watch, the more meteors you will likely see. And, although the peak of the meteor activity occurs on the morning of Oct. 21, you can still see a few Orionid meteors on the mornings of Oct. 20 and 22, as well.
Consider this a warm-up for 2061, when Halley’s Comet returns in person!
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Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College’s Alpine Campus. He is an avid astronomer whose photographs and articles have been published on the Web sites of CNN.com, NASA’s “Astronomy Picture of the Day” Web site, Spaceweather.com, Space.com, Discover.com, MSNBC.com, NationalGeographic.com, and in Sky & Telescope, Astronomy, Night Sky, Discover, and WeatherWise magazines. His “Celestial News” article appears weekly in the Steamboat Pilot & Today. His “Cosmic Moment” radio spots can be heard on local radio station KFMU. Also, check out Jimmy’s Web site at http://www.jwestlake.com.