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Orionids Meteor Shower

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Information on the Orionids Meteor Shower
Orion

Orion

Nick Greene
The Orionids -- so named because they appear to streak out of a point (called the radiant) in the constellation Orion -- will peak on October 21st. Sky watchers north of the equator with dark clear skies will spot 15 to 20 meteors each hour before dawn. Observers south of the equator will see almost as many: 10 to 15 per hour.

The October Orionids are cousins of the eta Aquarids -- a mostly southern hemisphere meteor shower in May. Both spring from Halley's Comet.

"Earth comes close to the orbit of Halley's Comet twice a year, once in May and again in October," explains Don Yeomans, manager of NASA's Near-Earth Object Program at the Jet Propulsion Laboratory. Although the comet itself is rarely nearby -- it's beyond the orbit of Saturn now -- Halley's dusty debris constantly moves through the inner solar system and causes the two regular meteor showers.

In 1986, the last time Halley's Comet swung past the Sun, solar heating evaporated about 6 meters of dust-laden ice from the comet's nucleus. That's typical, say researchers. The comet has been visiting the inner solar system every 76 years for millennia, shedding dust each time.

No one knows exactly how long it takes for a dust-sized piece of Halley to move to an Earth-crossing orbit -- perhaps centuries or even thousands of years. However, one thing is certain: "Orionid meteoroids are old."

And fast. "These meteoroids strike Earth's atmosphere traveling 66 km/s or 148,000 mph," he continued. Only the November Leonids (72 km/s) are faster. Such meteors often leave glowing "trains" (incandescent bits of debris in the wake of the meteor) that last for several seconds to minutes.

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