|In astronomy, there's nothing quite like a bright meteor streaking across the glittering canopy of a moonless night sky. The unexpected flash of light adds a dash of magic to an ordinary walk under the stars.|
Monday, August 12, 2013
ARCHIVE / GREAT BALLS OF FIRE / SUMMER SKY SHOW
WHAT ARE PERSEID FIREBALLS—NASA Guest Blog-- A fireball is a very bright meteor, at least as bright as the planets Jupiter or Venus. They can be seen on any given night as random meteoroids strike Earth's upper atmosphere. One fireball every few hours is not unusual. Fireballs become more numerous, however, when Earth is passing through the debris stream of a comet. That’s what will happen today and tomorrow (Aug. 12/13).
New research by NASA has just identified the most magical nights of all.
"We have found that one meteor shower produces more fireballs than any other," explains Bill Cooke of NASA's Meteoroid Environment Office. "It's the Perseid meteor shower, which peaks on August 12th and 13th."
The Perseid meteor shower comes from Comet Swift-Tuttle. Every year in early- to mid-August, Earth passes through a cloud of dust sputtered off the comet as it approaches the sun. Perseid meteoroids hitting our atmosphere at 132,000 mph produce an annual light show that is a favorite of many backyard sky watchers.
Cooke thinks the Perseids are rich in fireballs because of the size of the parent comet.
"Comet Swift-Tuttle has a huge nucleus--about 26 km in diameter," comments Cooke. "Most other comets are much smaller, with nuclei only a few kilometers across. As a result, Comet Swift-Tuttle produces a large number of meteoroids, many of which are large enough to produce fireballs."
Perseid Fireballs (histogram, 558px)
Since 2008, the Perseids have produced more fireballs than any other annual meteor shower. The Geminids are a close second, but they are not as bright as the Perseids. "The average peak magnitude for a Perseid observed by our cameras is -2.7; for the Geminids, it is -2," explains Bill Cooke. "So on average, Geminid fireballs are about a magnitude fainter than those in the Perseids."
Cooke recommends looking on the nights of August 12th and 13th between the hours of 10:30 PM to 4:30 AM local time. Before midnight the meteor rate will start out low, then increase as the night wears on, peaking before sunrise when the constellation Perseus is high in the sky.
For every fireball that streaks out of Perseus, there will be dozens more ordinary meteors.
"Get away from city lights," advises Cooke. "While fireballs can be seen from urban areas, the much greater number of faint Perseids is visible only from the countryside."
In total, the Perseid meteor rate from dark-sky sites could top 100 per hour.
That’s a lot of magic. Enjoy the show—Guest Blog By Dr. Tony Phillips/Science@NASA.com