ORIONID METEOR SHOWER OCTOBER 21, 2010

ORIONID METEOR SHOWER: Earth is entering a broad stream of debris from Halley's Comet, and this is causing the annual Orionid meteor shower. "The best time to look is during the hours before dawn on Thursday, Oct. 21st, and again on Friday, Oct 22nd," advises Bill Cooke of NASA's Meteoroid Environment Office. "Unfortunately, we have a bright Moon this year. Even so, I'd expect some bright Orionids to shine through the moonlight." An all-sky camera at the University of Western Ontario recorded this early Orionid fireball on Oct. 18th: Orionid meteors stream from the elbow of Orion the Hunter: sky map. Because the shower's radiant point is close to the celestial equator, sky watchers in both hemispheres can enjoy the show. Moonlit meteor rates will probably be around a dozen per hour.

Radar rates could be much higher. The US Air Force Space Surveillance Radar in Texas is scanning the skies for satellites, space junk, and meteoroids. When an Orionid passes overhead--ping!--there is an echo. Moonlight does not interfere with this method of meteor observing, so it's perfect for this year's Orionids. Tune into Spaceweather Radio for live echoes.

TIME TO SEE COMET HARTLEY: For backyard stargazers, now is the best time to see green Comet 103P/Hartley 2 as it approaches Earth for an 11-million-mile close encounter on Oct. 20th. Set your alarm for the dark hours before dawn, go outside, and look straight up. You will find Hartley 2 not far from the bright star Capella: sky map. Although the comet is barely visible to the unaided eye, it is easy to find in binoculars and looks great through a backyard telescope.

"I observed Comet Hartley 2 at dawn on October 20, 2010, at its closest approach to Earth," says amateur astronomer Alan Dyer, who sends this picture from a dark-sky site near Cluny, Alberta, Canada:

"Apart from the blue-green color, this view matches what the comet looked like visually through large binoculars — a round fuzzball," says Dyer.

Many readers have asked, why is the comet green? Answer: Hartley 2's green color comes from the gases that make up its Jupiter-sized atmosphere. Jets spewing from the comet's nucleus contain cyanogen (CN: a poisonous gas found in many comets) and diatomic carbon (C2). Both substances glow green when illuminated by sunlight in the near-vacuum of space.

NASA scientists say 103P/Hartley 2 is one of the most active comets they've seen, with copious outgassing from jets in the nucleus. Amateur astronomers are encouraged to monitor the action...

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Science & Technology

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