Dust particles shed by Halley's Comet create our annual Orionid meteor shower, which peaks on the morning of Oct. 21 every year. Shown here (lower left) as it appeared in our sky on March 17, 1986, Halley's Comet itself won't be seen from Earth again until the year 2061.
Tuesday, October 13, 2009
Jimmy Westlake's Celestial News column appears Tuesdays in the Steamboat Today.
Find more columns by Westlake here.
Did you get to see Halley's Comet when it sailed past Earth in 1985 and '86? If not, you'll have to wait until the year 2061 for another chance, because 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 our annual Aquarid and Orionid meteor showers.
Comets are like big, dirty snowballs that hover near the outer edges of the solar system in perpetual cold and dark. But every so often, the gravity of the sun tugs 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 clouds of steam and millions of tiny dust grains trapped in the ice. The combined forces of sunlight and solar wind blow the gaseous vapors away from the snowball, forming the comet's graceful, flowing tail and filling the comet's path with dusty debris. After a comet has made many passes around the sun, its orbit may fill with dusty debris, like a river of dust in space.
The Earth crosses Halley's dust river twice each year, once on May 5 and again on Oct. 21. When one of these dust particles plows into the Earth's upper atmosphere at nearly 150,000 mph, it incinerates in a brief but brilliant flash of light called a meteor. Cometary dust grains are so small that you could easily hold 1,000 of them in the cupped palm of your hand.
This October's Orionid meteor shower will peak between the hours of midnight and dawn on the morning of Oct. 21. A single observer with the benefit of dark, clear skies might see between one and two dozen meteors, or "shooting stars," each hour. The slender crescent moon will set early in the evening this year, leaving the sky nice and dark for meteor watching.
The October meteors that Halley's Comet sends our way are called Orionid meteors because they seem to fan out from a point in the sky near the familiar star pattern of Orion the Hunter. Orion doesn't rise above our eastern horizon until about 11 p.m. in late October, so don't expect to see many meteors before midnight. You'll see Orionid meteors in every part of the sky, but they will all point 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, as the Earth rotates us more in the direction of Orion. 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 the Orionid meteor shower a warm-up for 2061, when Halley's Comet itself returns.
Westlake teaches astronomy and physics at Colorado Mountain College's Alpine Campus. He is an avid astronomer whose photographs and articles have been published all around the world. Check out Jimmy's Web site at www.jwestlake.com.