[meteorite-list] Perseid Fireballs

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 26 Jul 2013 22:28:19 -0700 (PDT)
Message-ID: <201307270528.r6R5SJ6Y012283_at_zagami.jpl.nasa.gov>

http://science.nasa.gov/science-news/science-at-nasa/2013/26jul_perseids/

Perseid Fireballs
NASA Science News
July 26, 2013

July 26, 2013: 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.

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."

Using a network of meteor cameras distributed across the southern USA,
Cooke's team has been tracking fireball activity since 2008, and they
have built up a database of hundreds of events to analyze. The data point
to the Perseids as the 'fireball champion' of annual meteor showers.
Auroras Underfoot (signup)

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 this August.

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."

[Graphic]
Perseid Fireballs (histogram)
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.

Credits:

Author:Dr. Tony Phillips
Production editor: Dr. Tony Phillips
Credit: Science at NASA
Received on Sat 27 Jul 2013 01:28:19 AM PDT