Weekend Meteor Shower   
       
   Oct. 20, 2011: Earth is about to pass through a stream of debris from Halley's   
   comet, source of the annual Orionid meteor shower. Forecasters expect more   
   than 15 meteors per hour to fly across the sky on Saturday morning, Oct. 22nd,   
   when the shower peaks.   
       
   http://science.nasa.gov/media/medialibrary/2008/08/10/19oct_magicalmorning_re   
   sources/meteor.jpg   
       
   Orionids are most easily seen during the dark hours before sunrise. Twilight   
   Orionids, however, are the most beautiful of all. "Although this isn't the   
   biggest meteor shower of the year, it's definitely worth waking up for," says   
   Bill Cooke of the NASA Meteoroid Environment Office. "The setting is dynamite."   
       
   Orionids are framed by some of the brightest and most beautiful constellations   
   in the night sky. The meteors emerge from mighty Orion, the shower's   
   glittering namesake.  From there they streak through Taurus the Bull, the   
   twins of Gemini, Leo the Lion, and Canis Major--home to Sirius, the most   
   brilliant star of all.   
       
   This year, the Moon and Mars are part of the show.  They'll form two vertices   
   of a celestial triangle in the eastern sky on Saturday morning while the   
   shower is most active; Regulus is the third vertex.  Blue Regulus and red Mars   
   are both approximately of 1st magnitude, so they are easy to see alongside the   
   35% crescent Moon.  Many Orionids will be diving through the triangle in the   
   hours before dawn.   
       
   Cooke's team at the Meteoroid Environment Office will be watching for Orionids   
   that actually hit the Moon.   
       
   Cometary debris streams like Halley's are so wide, the whole Earth-Moon system   
   fits inside. So when there is a meteor shower on Earth, there's usually one on   
   the Moon, too.  Unlike Earth, however, the Moon has no atmosphere to intercept   
   meteoroids.  Pieces of debris fall all the way to the surface and explode   
   where they hit.  Flashes of light caused by thermal heating of lunar rocks and   
   moondust are so bright, they can sometimes be seen through backyard-class   
   telescopes.   
       
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   A map of the morning sky on Saturday, Oct. 22nd at 5:30 a.m. local time,   
   viewed facing southeast. Click to view a larger, more complete map.   
   "Since we began our monitoring program in 2005, our group has detected more   
   than 250 lunar meteors," says Cooke. "Some explode with energies exceeding   
   hundreds of pounds of TNT."   
       
   So far, they've seen 15 Orionids hitting the Moon--"two in 2007, four in 2008,   
   and nine in 2009," recalls Cooke.  This year they hope to add to the haul.    
   About 25% of the Moon's dark terrain will be exposed to Halley's debris   
   stream, giving the team millions of square miles to scan for explosions.   
       
   Watching meteoroids hit the Moon is a good way to learn about the structure of   
   comet debris streams and the energy of the particles therein.  It also allows   
   Cooke and colleagues to calculate risk factors for astronauts who, someday,   
   will walk on the lunar surface again.   
       
   "Going outside to watch the Orionids might not be a good idea for a   
   moonwalker," says Cooke.   
       
   But it is a good idea for the rest of us.  Set your alarm for a few hours   
   before dawn on Saturday morning and enjoy the show.   
       
       
   Author: Dr. Tony Phillips | Credit: Science@NASA   
       
   More Information   
   Lunar Impact Monitoring News -- from the NASA Meteoroid Environment Office   
       
   International Meteor Organization -- live Orionid meteor counts   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.64   
    * Origin: NCS BBS (1:3828/7)