Hallo from Halley's comet

Oct 19, 2007 09:08 GMT  ·  By

Are you ready? You will not see this again until next year: Halley's comet will bring forth the magnificent Orionid meteor shower at its peak this week. The show is triggered by fragments of this "king star" amongst other comets. You could see these days 15 or 20 meteors an hour by the naked eye.

The Orionid shower is not the most impressive, but the most predictable one in timing and intensity.

"They are pretty much an Old Faithful type of reliable shower," said Alan MacRobert, a senior editor at Sky and Telescope magazine, alluding to the famous geyser from Yellowstone National Park.

This year the moon brings its own contribution, by setting and this leaves darker skies which improve meteor sightings. "We have a window of moonless sky, so this is one for which regular meteor observers are going to be out," said MacRobert.

The best moment will be the early morning hours of October 21 but the shower is visible from October 20 to 24. The best hours are between moonset (after midnight) and the start of dawn some 90 minutes before sunrise.

The Orionid showers are induced by the Halley's comet expelling dust particles as it rotates around the sun. Earth crosses the comet's path annually, and now is the moment when the dust cloud is formed. The fragments enter the Earth's atmosphere at about 42 mi (67 km) per second, superheating the air molecules at temperatures that make them shine.

"Most of the things that make a nice, good visual meteor are the size of a grain of sand. This is a wide stream, so it will take a couple of days to completely pass through. People all over Earth will have a chance to see the meteors. Meteors are hitting all the time even in daylight, although it's too bright to see them." said Scott Sandford, an astrophysicist at NASA's Ames Research Center at Moffett Field, California.

The whole phenomenon occurs 50 - 70 mi (80 - 110 km) aloft, but it's clearly visible from the ground. The route of the Orionids appears to point towards the constellation Orion, but in fact it occurs all over the sky. The best way to see it is to focus on the sky's darkest area and avoid artificial light, which dims the show.