The 2011 Geminid Meteor Shower   
       
   Dec. 13, 2011: The 2011 Geminid meteor shower peaks on the night of Dec.   
   13-14, and despite the glare of a nearly-full Moon, it might be a good show.   
       
   "Observers with clear skies could see as many as 40 Geminids per hour,"   
   predicts Bill Cooke of the NASA Meteoroid Environment Office.  "Our all-sky   
   network of meteor cameras has captured several early Geminid fireballs.  They   
   were so bright, we could see them despite the moonlight."   
       
   [...]   
       
   An early Geminid fireball recorded on Dec. 11th by a NASA meteor network   
   camera in Tennessee. [movie]   
       
   The best time to look is between 10 pm local time on Tuesday, Dec. 13, and   
   sunrise on Wednesday, Dec. 14th. Geminids, which spray out of the   
   constellation Gemini, can appear anywhere in the sky. "Dress warmly and look   
   up," says Cooke.  "It's that simple."   
       
   The source of the Geminids is near-Earth asteroid 3200 Phaethon. Most meteor   
   showers come from comets, so having an asteroid as a parent makes the Geminids   
   a bit of an oddball.   
       
   "This is the thing I love most about Geminids," says Cooke.  "They're so   
   strange."   
       
   Every year in mid-December, Earth runs through a trail of dusty debris that   
   litters the orbit of 3200 Phaethon. Comets vaporizing in hot sunlight   
   naturally produce such debris trails, but rocky asteroids like 3200 Phaethon   
   do not. At least they're not supposed to. The incongruity has baffled   
   researchers since 1983 when 3200 Phaethon was discovered by NASA's IRAS   
   satellite.   
       
   One clue: 3200 Phaethon travels unusually close to the sun. The asteroid's   
   eccentric orbit brings it well inside the orbit of Mercury every 1.4 years.   
   The rocky body thus receives a regular blast of solar heating that might   
   somehow boil jets of dust into the Geminid debris stream.   
       
   [...]   
       
   Click to view a full-sized sky map. Credit: Tony Phillips In 2009, NASA's   
   STEREO-A spacecraft saw this process at work.  Coronagraphs onboard the solar   
   observatory watched 3200 Phaethon as it was swinging by the sun.  Sure enough,   
   the asteroid doubled in brightness, probably because it was spewing jets of   
   dust.   
       
   "The most likely explanation is that Phaethon ejected dust, perhaps in   
   response to a break-down of surface rocks (through thermal fracture and   
   decomposition cracking of hydrated minerals) in the intense heat of the Sun,"   
   wrote UCLA planetary scientists David Jewitt and Jing Li, who analyzed the   
   data.   
       
   Jewett and Li's "rock comet" hypothesis is compelling, but they point out a   
   problem: The amount of dust 3200 Phaethon ejected during its 2009   
   sun-encounter added a mere 0.01% to the mass of the Geminid debris stream--not   
   nearly enough to keep the stream replenished over time. Perhaps the rock comet   
   was more active in the past .?   
       
   "We just don't know," says Cooke. "Every new thing we learn about the Geminids   
   seems to deepen the mystery."   
       
   Led by Cooke, the Meteoroid Environment Office has just released an app for   
   iPhones and iPads to help citizen scientists count meteors and report their   
   observations to NASA. The "Meteor Counter" is available for free from Apple's   
   app store:   
       
   http://itunes.apple.com/us/app/meteor-counter/id466896415   
       
   Cooke hopes sky watchers everywhere will use it to monitor the mysterious   
   Geminids.   
       
       
   Author:Dr. Tony Phillips| Production editor: Dr. Tony Phillips | Credit:   
   Science@NASA   
       
   More Information   
   ACTIVITY IN GEMINID PARENT (3200) PHAETHON -- The Astronomical Journal,   
   140:1519-1527, 2010 November   
       
   (3200) Phaethon: A Rock Comet by David Jewitt and Jing Li, UCLA   
       
   Complete instructions for using the Meteor Counter app are available at:   
   http://meteorcounter.com/   
   NASA astronomer Bill Cooke is head of the NASA Meteoroid Environment Office   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.64   
    * Origin: NCS BBS (1:3828/7)