From five key points on the globe and from the International
Space Station, NASA researchers will use special cameras to
scan the skies and report activity around the clock during
the annual Leonid meteor shower Nov. 18-19.
Sky-gazers in North America and Europe should be able to
“catch” as many as one meteor every 6 to 10 seconds — even
with a full moon shining — during the peak of the Leonid
meteor shower, which occurs when Earth passes close to the
orbit of the Comet Tempel-Tuttle and debris left in the
comet’s path.
Led by the Engineering Directorate at NASA’s Marshall Space
Flight Center in Huntsville, Ala., the research is part of
a long-term goal to protect spacecraft such as NASA’s
Chandra X-ray Observatory from potentially damaging
meteoroids.
“Stargazers should see a great show, even though the full
moon will cut visibility about 75 percent,” said Dr. Rob
Suggs, the Space Environments Team Lead. “For the past
three years, we’ve had some astounding Leonid showers.
However, this may be the last opportunity in our lifetimes
to see a ‘storm’ of Leonids. Predictions lead us to
believe this could be the ‘grand finale’ until 2133.”
Using “night-vision” image intensifier video systems and
sky-watchers outfitted with Palm computer software
developed to record visual counts, NASA engineers and
astronomers will record their observations for later
analysis.
Despite what their name suggests, “shooting stars” are not
stars at all; they are meteors. Meteors are produced when
bits of cometary or asteroidal debris in space, usually
between the size of a sand grain and a pebble, enter the
Earth’s atmosphere and burn up, creating a brief — usually
white — streak of light.
The Leonids were named such because they appear to radiate
out of the constellation Leo. The material crossing Earth’s
path this year was ejected from the Comet Tempel-Tuttle at
least 100 years ago. Meteor viewers in the United States,
for example, will see material ejected from the comet in
1866.
NASA engineers have provided meteor shower rates for many
cities around the world through the NASA Web site:
www.SpaceWeather.com sponsored by Science@NASA (http://science.nasa.gov)
Astronomer Mitzi Adams of the Marshall Center also will
provide updates Nov. 18 on the progress of the Leonids to
SpaceWeather.com .
NASA’s concern, however, isn’t the view. Even though
today’s satellites are engineered to withstand a smattering
of meteoroid strikes, by determining where, when and how
the meteors will strike, NASA can take protective measures
to prevent or minimize damage to spacecraft.
Because the stream from Tempel-Tuttle hits the Earth almost
head-on, the Leonids are among the fastest meteors known —
entering the Earth’s atmosphere at 44 miles per second.
Since the Chandra Observatory must travel through the Leonid
debris field, controllers at its Operations Control Center
in Cambridge, Mass., will make sure the satellite is pointed
in the exact opposite direction as the incoming meteors.
They will angle the solar arrays to protect the sensitive
back of the arrays and minimize the surface area presented
to the meteor direction.
Protective measures can range from turning a satellite so
it faces the direction of minimal exposed surface area, to
shutting down a spacecraft’s electronic operations until
the storm has passed.
“When a meteoroid hits a satellite, it can heat the impact
site to thousands of degrees Kelvin — rivaling the surface
temperature of the Sun,” Suggs said. “Usually the entire
meteoroid is vaporized along with a tiny bit of the
spacecraft.”
Considering that meteors are so small, their potential for
damage can be surprising when their speed is considered.
“They’re small, but they move very fast — about 45 miles
per second (71 kilometers per second),” said Dr. Bill
Cooke, an astronomer at the Marshall Center.
Cooke says the research data from the Leonid shower will
be analyzed to help NASA engineers refine their engineering
forecasts for spacecraft.
According to Cooke, sky-gazers could see up to 600 meteors
per hour if they are away from city lights and the sky is
clear. In the Eastern United States, the shower is predicted
to peak near dawn, while in the Western United States, it is
expected to peak around 2:30 a.m. PST. However, the “show”
will start Nov. 18 about 10:53 EST with the Leonid
“grazers” — meteors not dropping into the Earth’s
atmosphere, but instead grazing the atmosphere. Grazers
appear as reddish meteors that advance east to west across
a large part of the sky.
The NASA researchers will monitor the storm from five
locations, each selected based on meteor forecasts and
the area’s climate. Sites include Huntsville, Ala.; Calar
Alto Observatory in southern Spain; Teide Observatory in
the Canary Islands; Apache Point Observatory in southern
New Mexico; and Kitt Peak National Observatory in southern
Arizona.
Another tool at Marshall’s disposal is “forward-scatter
radar” — an early warning system built by Suggs, Cooke
and Dr. Jeff Anderson, also of Marshall’s Engineering
Directorate.
“Our system is pretty simple,” said Suggs. “We use an
antenna and computer-controlled short-wave receiver to
listen for 67 MHz signals from distant TV stations.”
The transmitters are over the horizon and normally out of
range. When a meteor streaks overhead, the system records
a brief ping — the echo of a TV signal bouncing off the
meteor’s trail. Like the image-intensified cameras, this
system is capable of detecting meteors too dim to see
with the unaided eye.
The Marshall Center has also provided Leonid forecast
information to operators of spacecraft such as Chandra
to help prepare for a meteor shower. “By comparing the
meteor shower predictions to the actual meteor counts,
we are laying the groundwork to improve forecasts in the
future,” said Suggs.
How to view Leonids:
The golden rule to watching the Leonids — or any meteor
shower — is to be comfortable, according to Cooke and
Suggs. Be sure to wrap up warmly — a sleeping bag placed
atop a lawn chair facing east is a good way to enjoy the
show. Put your chair in a clear, dark place with a view
of as much of the sky as possible. Don’t stare at any one
place — keep your eyes moving across the sky. Watch for
fireballs and streaks — some will remain visible for
several minutes or more. The meteors will be radiating
from the Sickle of Leo that will be rising out of the
east-northeast sky. Don’t look directly at the
constellation, but at the area above and around it. And,
though you don’t need them to see the Leonids, a pair of
binoculars could come in handy.
For more information:
IMAGE CAPTION:
[http://www1.msfc.nasa.gov/NEWSROOM/news/photos/2002/2002images/Hall1_m.jpg]
2001 Leonids shower. (Photo credit: Sam Cook of Chattanooga,
Tenn., copyrighted)
