Spring is Fireball Season   
   March 31, 2011: What are the signs of spring? They are as familiar as a   
   blooming Daffodil, a songbird at dawn, a surprising shaft of warmth from the   
   afternoon sun.   
       
   And, oh yes, don't forget the meteors.   
       
   "Spring is fireball season," says Bill Cooke of NASA's Meteoroid Environment   
   Center. "For reasons we don't fully understand, the rate of bright meteors   
   climbs during the weeks around the vernal equinox."   
   [...]   
   A spring fireball recorded by a NASA all-sky camera located at the Marshall   
   Space Flight Center on March 16, 2009. [movie]   
       
   In other seasons, a person willing to watch the sky from dusk to dawn could   
   expect to see around 10 random or "sporadic" fireballs. A fireball is a meteor   
   brighter than the planet Venus. Earth is bombarded by them as our planet plows   
   through the jetsam and flotsam of space--i.e., fragments of broken asteroids   
   and decaying comets that litter the inner solar system.   
       
   In spring, fireballs are more abundant. Their nightly rate mysteriously climbs   
   10% to 30%.   
       
   "We've known about this phenomenon for more than 30 years," says Cooke. "It's   
   not only fireballs that are affected. Meteorite falls--space rocks that   
   actually hit the ground--are more common in spring as well1."   
       
   Researchers who study Earth's meteoroid environment have never come up with a   
   satisfactory explanation for the extra fireballs. In fact, the more they think   
   about it, the stranger it gets.   
       
   Consider the following:   
   [...]   
   A NASA fireball camera at the Marshall Space Flight Center. [more] There is a   
   point in the heavens called the "apex of Earth's way." It is, simply, the   
   direction our planet is traveling. As Earth circles the sun, the apex circles   
   the heavens, completing one trip through the Zodiac every year.   
       
   The apex is significant because it is where sporadic meteors are supposed to   
   come from. If Earth were a car, the apex would be the front windshield. When a   
   car drives down a country road, insects accumulate on the glass up front.   
   Ditto for meteoroids swept up by Earth.   
       
   Every autumn, the apex climbs to its highest point in the night sky. At that   
   time, sporadic meteors of ordinary brightness are seen in abundance, sometimes   
   dozens per night.   
       
   Read that again: Every autumn.   
       
   "Autumn is the season for sporadic meteors," says Cooke. "So why are the   
   sporadic fireballs peaking in spring? That is the mystery."   
       
   Meteoroid expert Peter Brown of the University of Western Ontario notes that   
   "some researchers think there might be an intrinsic variation in the meteoroid   
   population along Earth's orbit, with a peak in big fireball-producing debris   
   around spring and early summer. We probably won't know the answer until we   
   learn more about their orbits2."   
       
   To solve this and other puzzles, Cooke is setting up a network of smart meteor   
   cameras around the country to photograph fireballs and triangulate their   
   orbits. As explained in the Science@NASA story What's Hitting Earth?, he's   
   looking for places to put his cameras; educators are encouraged to get   
   involved. Networked observations of spring fireballs could ultimately reveal   
   their origin.   
       
   "It might take a few years to collect enough data," he cautions.   
       
   Until then, it's a beautiful mystery. Go out and enjoy the night sky. It is   
   spring, after all.   
       
       
   Author: Dr. Tony Phillips | Credit: Science@NASA   
       
   More Information   
   NASA's All-Sky Fireball Network -- check this website to view last night's   
   fireballs   
       
   Footnotes:   
       
   (1) A Study on the Relative Rates of Meteorite Falls on Earth's Surface -- by   
   Ian Halliday and Arthur A. Griffin, Meteoritics, Vol. 17, No. 1, March 31, 1982   
       
   (2) Peter Brown notes that the antapex of Earth's way is highest in spring.   
   The antapex is the opposite of the apex. It is the direction Earth is heading   
   away from. Could the sporadic fireballs be coming from the antapex? "There's   
   no evidence for an antapex source of fireballs. Precise details are still   
   unclear, however, in part due to lack of fireball data from different   
   latitudes."   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.59   
    * Origin: NCS BBS (1:3828/7)