Celestial News: Here come the Orionid meteors
October 19, 2017
Did you see Halley's Comet when it sailed past Earth in 1985 to 86? If you missed it, you'll have to wait until 2061-62 for another chance, because Halley's Comet only comes around these parts 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 our 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 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. After a comet has made numerous trips around the sun, its orbit can fill up with dusty debris, like a river of dust particles in space.
The Earth crosses Halley's Comet's dusty wake twice each year, once in early May and mid October. When one of these dust particles plows into the Earth's upper atmosphere at nearly 150,000 mph, it burns up 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 in the predawn hours of Saturday, Oct. 21. A single observer under dark, clear skies can expect to see about 20 Orionid meteors per hour near the peak. The three-day old crescent moon will set early Friday evening, leaving the sky nice and dark for meteor watching Saturday morning.
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 winter star pattern of Orion the Hunter. Orion doesn't rise above our eastern horizon until about 11 p.m. in mid October, so don't expect to see many meteors before midnight. Orionid meteors will appear in every part of the sky, but they will all trace back to a common origin near the bright star Betelgeuse, the star marking Orion's left shoulder, high up in the southeastern sky by 4 a.m. The closer to dawn you watch, the more meteors you are likely to see. This is because the Earth rotates us more in the direction of Orion as we approach sunrise.
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Tthough the peak of the meteor activity occurs on the morning of Oct. 21, you also might see a few Orionid meteors zipping across the sky on the mornings of Oct. 20 and 22 as well.
Jimmy Westlake recently retired from full time teaching at Colorado Mountain College's Steamboat campus, after nineteen years as their professor of physical sciences, and is looking forward to spending a lot more time under the starry sky. His Celestial News column appears in the Steamboat Today newspaper monthly. Check out Westlake's astrophotography website at jwestlake.com.