'Catch a shooting star!' NASA engineers to scan for Leonid m

by Steve Roy of Marshall Space Flight Center

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From five key points on the globe and the International Space Station, researchers at the Marshall Center will use special cameras to scan the skies during the annual Leonid meteor shower Nov. 18-19. They will report activity around the clock to protect spacecraft such as NASA's Chandra X-ray Observatory from potentially damaging meteoroids. By determining where, when and how the meteors will strike, NASA can take protective measures to prevent or minimize damage to spacecraft. Live TV and radios interviews with a Marshall astronomer will be available Nov. 18.

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.

Photo: 2001 Leonids shower. (Photo credit: Sam Cook of Chattanooga, Tenn., copyrighted)

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:

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.

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