July 29, 2013
Perseids Identified By NASA As Most Active Annual Meteor Shower
[ Watch the Video: ScienceCasts: Perseid Fireballs ]
Brett Smith for redOrbit.com - Your Universe OnlineMeteor showers are some of the most exciting and unpredictable displays of nature and a team of NASA astronomers have just identified one shower as the most active of any annual display.
"We have found that one meteor shower produces more fireballs than any other," said Bill Cooke of NASA's Meteoroid Environment Office (MEO). "It's the Perseid meteor shower, which peaks on August 12th and 13th."
Astronomers consider a fireball to be as bright as Jupiter or Venus in the night sky. Although they can be seen on any given night, fireballs appear more frequently when Earth's orbit carries it through the debris stream of a comet, as it will in the second full week of August.
Perseids come from Swift-Tuttle, a larger-than-normal comet that is prone to leaving a big debris field in its wake.
"Comet Swift-Tuttle has a huge nucleus--about (16 miles) in diameter," Cooke said. "Most other comets are much smaller, with nuclei [a little more than a mile] across. As a result, Comet Swift-Tuttle produces a large number of meteoroids, many of which are large enough to produce fireballs."
Earth passes through the comet's debris cloud around the same time each year -- late July to mid-August. Swift-Tuttle takes 133 years to complete its orbit and the annual meteor shower is the result of meteoroids coming off the comet the last time it approached the sun.
When the Perseids hit Earth's atmosphere, they do so at around 132,000 mph. The friction produced by all those collisions makes for an annual light show that has become a favorite of many nighttime sky watchers.
Using a system of specifically calibrated cameras distributed across the southern US, Cooke's team has been recording fireball activity since 2008. According to their data, the Perseids have produced more fireballs than any other meteor shower in the last five years. During the same time span, the Geminid meteor shower has produced about 140 less than the Perseids. Also, the December shower's fireballs aren't typically 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," Cooke explained. "So on average, Geminid fireballs are about a magnitude fainter than those in the Perseids."
The NASA scientists recommend looking for the Perseid fireballs on the nights of August 12th and 13th between 10:30 pm and 4:30 am local time. Earlier in the night, the rate of fireballs will be fairly low and increase as the night turns to early morning. Peak fireball activity typically occurs just before sunrise when the constellation Perseus is high in the early morning sky.
"Get away from city lights," Cooke suggested. "While fireballs can be seen from urban areas, the much greater number of faint Perseids is visible only from the countryside."
According to NASA, for every visible fireball, there are dozens of other meteors. Those in rural areas without much light pollution can expect to see around 100 fireballs per hour.
The Orinids are the next major meteor shower to occur after the Perseids. The fireballs from Halley's Comet are expected to peak in activity around mid-October.