Leonid Meteor Balloon Rises Again
Right: Scores of meteors rained down over western Europe during the 1999 Leonids shower. Dazzled observers saw brief scenes like this one, captured by A. Scott Murrell during the 1966 Leonid storm. [credits]
Meteor watching under a crisp November sky with twinkling stars and bright planets is an experience that's hard to beat -- even at 3 in the morning! But if clouds, rain, or city lights threaten to spoil your pre-dawn stargazing adventure, NASA scientists are prepared to help.
Before dawn on Saturday, Nov. 18th, a team of astronomers and ham radio amateurs at NASA's Marshall Space Flight Center (MSFC) plan to launch a specially-equipped weather balloon to monitor the Leonid meteor shower 100,000 feet above Earth's surface, far from obscuring clouds and urban light pollution. Video from the flight will be broadcast live on the web at LeonidsLive.com and replays will be available less than 24 hours later.
This will be the third annual Science@NASA-sponsored broadcast of the Leonids from the stratosphere. In 1998 and 1999 more than two million people watched live webcasts during the meteor shower or saw replays the morning after.
This year's liftoff is scheduled for 0630 Greenwich Mean Time (0030 CST) on Saturday, Nov. 18th, from the Marshall Space Flight Center's Atmospheric Research Facility (ARF). The balloon will carry a sensitive low-light CCD video camera to monitor the shower from an altitude of about 32 km (100,000 ft).
"Earth is going to pass through the outskirts of three meteoroid debris streams from comet Tempel-Tuttle on Nov. 17th and 18th," says Marshall astronomer Mitzi Adams. "The last of the three stream encounters will take place at approximately 0800 GMT on Nov. 18th, just as the meteor balloon is reaching its maximum altitude. The timing couldn't be better."
"The balloon will carry a sensitive CCD camera to record the meteors," added Ed Myszka, an engineer and radio amateur who built the balloon payload. "The field of view will be about 20 degrees. That's about twice the size of the bowl of the Big Dipper.
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Sound effects during this year's flight will be provided by an INSPIRE VLF radio receiver, which is sensitive to radio emissions below 10 kHz. The very low frequency (VLF) radio band is filled with exotic-sounding signals called spherics, tweeks and whistlers. All three are impulsive bursts caused by distant lighting. "Spherics," which are caused by lightning strokes within a couple of thousand kilometers of the receiver, sound like twigs snapping or bacon sizzling on a grill. Tweeks and whistlers are caused by more distant lightning, and sound like brief descending musical tones.
Dennis Gallagher, a plasma physicist at the Marshall Space Flight Center, thinks that the VLF receiver might also pick up natural radio emissions from the Leonid meteors.
"Meteoroids produce an ionized trail as they plow through the atmosphere," explained Gallagher. "There's a low density wake right behind the meteoroid. Because electrons are more mobile than protons, they move in to fill the void faster. That could set up plasma oscillations and trigger radio emissions."
The VLF receiver was donated to the Marshall Space Flight Center for this and future flights by the Goddard INSPIRE program. It's been christened the "Marina receiver" after the daughter of Flavio Gori, an Italian scientist who first suggested flying the receiver.
Above: This time-frequency plot (or dynamic spectrum) shows two whistlers, one at 9 minutes and one at 12 minutes. They are caused by VLF radio emissions from lightning strokes that travel long distances along magnetic field lines. Other types of VLF radio emissions include tweeks, chorus, and spherics. To learn more about the physics of these emissions, click here. To hear what they sound like, click here.
Gallagher and his colleagues also plan to operate another VLF receiver at the launch site to provide a ground reference for comparison with data collected from the stratosphere. During the flight, signals from the receiver will be converted to audio sounds and transmitted along with images from the CCD video camera. Web viewers at LeonidsLive.com will be treated to an unusual combination of meteoritic sights and sounds.
The question of radio emissions from meteors is an intriguing one, says Gallagher, and you don't need to send your receiver to the stratosphere to listen in. Anyone with a VLF receiver can monitor the Leonids on November 18 and Gallagher hopes that INSPIRE participants across the USA will join in the effort. The best way to collect data is to record the output of the receiver on a two-track audio recorder. Record the VLF signal on one track and a WWV time signal on the other. This way VLF pulses can be correlated with the times of bright meteors seen from your observing site. It's also a good idea to conduct at least one observing session a few days before or a few days after the Leonids for comparison.
For more information about the Leonids 2000, including predictions and observing tips, please visit LeonidsLive.com. Daily meteor counts and information about other meteor showers are available at SpaceWeather.com.Web Links
Leonids Live! - site of the meteor balloon webcast.
More Science@NASA stories about the Leonids
Lunar Leonids 2000 -- The Moon is heading for a close encounter with a Leonid debris stream on Nov. 17, 2000.
The Moonlit Leonids 2000 -- what to expect from this year's Leonids
1999 Leonids Rain in Spain -- find out what happened last year
Leonids on the Moon -- Science@NASA suggests that astronomers watch out for impact flashes in 1999
The 1998 Leonids -- Professionals and amateurs alike were impressed by the fiery show
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|For lesson plans and educational activities related to breaking science news, please visit Thursday's Classroom||Author: Dr. Tony Phillips
Production Editor: Dr. Tony Phillips
Curator: Bryan Walls
Media Relations: Steve Roy
Responsible NASA official: John M. Horack