Jimmy Westlake: Here come the Orionid meteors
October 8, 2012
Did you see Halley's Comet when it sailed past Earth in 1985 and 1986? If not, you'll have to wait until 2061 for another chance, because Halley's Comet only comes around once every 76 years. 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 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 that were trapped in the ice. The combined pressures of sunlight and the 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 trips around the sun, its orbit can fill with dusty debris, like a river of dust in space.
The Earth crosses Halley's Comet's dust river twice each year, once on May 5 and again on Oct. 20. 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 easily could hold 1,000 of them in the palm of your hand.
October's Orionid meteor shower will peak between midnight and dawn on the morning of Oct. 20. A single observer with dark, clear skies might see one to two dozen meteors, or "shooting stars," each hour.
The October meteors that Halley's Comet sends our way are called Orionid meteors because they appear 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 the bright star Betelgeuse, marking Orion's shoulder, high in the southeastern sky at about 4 a.m. The closer to dawn you watch, the more meteors you will likely see. This is because the Earth rotates us more in the direction of Orion as we near sunrise. Watching Orionid meteors perhaps is the next best thing to seeing Halley's Comet itself.
Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College's Alpine Campus.