A Spaceship Among Meteors
When the Leonid meteor storm crests over North America on Tuesday morning, an odd yet beautiful light will appear among the shooting stars. It'll be as bright as a Leonid fireball but slower moving and without a tail. And it won't come from the constellation Leo.
It's really a spaceship: the International Space Station (ISS).
Right: The International Space Station photographed on Oct. 16, 2002, by the crew of the space shuttle Atlantis. [more]
The table below summarizes some of the best apparitions. It's only a partial list. Cities not mentioned might nevertheless have good flybys, so check for your hometown using one of these three popular websites: J-Pass, Heavens-Above or SkyWatch.
The space station shines by reflecting sunlight. This means the ISS has to be out of Earth's shadow for you to see it. One of the most remarkable flybys on Tuesday morning will occur over Washington DC. At 5:10 a.m. EST, the station will emerge from Earth's shadow almost directly above the capital city. Sky watchers looking straight up will see the station flare from invisibility to Venus-like brightness in only a few moments. Such events are called "space station supernovas." Another space station supernova will happen over San Francisco a few hours later, at 5:15 a.m. PST.
*Bold-faced city names indicate places where the sky watchers will see a "space station supernova."
Above: Local times when the space station will appear over selected US cities. In most cases, the station will emerge over the northwest horizon, sail overhead (or nearly so), and disappear again in the southeast. Sky watchers will see something different, however, from cities indicated in bold where the ISS will materialize nearly overhead. Sky maps are courtesy of Heavens Above.
It takes the space station about 5 minutes to cross the sky. During that time, you might see dozens of Leonid meteors. Those meteors are much closer to Earth than the ISS is. "Meteors are specks of comet dust (called meteoroids) that burn up in Earth's atmosphere about 100 km high," explains Bill Cooke of the Marshall Space Flight Center's Space Environments Team. "The ISS, on the other hand, orbits Earth at an altitude of 400 km." That's why astronauts onboard the space station have to look down, not up, see the Leonids.
Like Earth itself, the space station will be inside the cloud of comet dust that causes the shower. Leonid meteoroids race by the station traveling 140,000 mph--unseen until they hit Earth's atmosphere below.
"Not really," answers Cooke. "Most Leonid meteoroids are nearly microscopic and very fragile. They can't penetrate the station's armor." Furthermore, he says, "the station is not a big target. The chances of it being hit by a meteoroid 5 cm across--that's the size of comet debris that causes the brightest Leonid fireballs--is about 1 in 10 billion."
Above: Tiny comet flakes like this are at the heart of fiery-looking Leonid meteors. This one is only 10 microns across. [more]
Those odds are why astronauts can relax and enjoy the show. Last year ISS commander Frank Culbertson watched the Leonids from orbit: "There were hundreds per minute going beneath us, really spectacular!" he recalled in the Science@NASA story Space Station Meteor Shower.
You can enjoy it, too, from Earth's surface. And if you spy a spaceship flying among the meteoroids ... so much the better.
Visit SpaceWeather.com or watch The Leonids TV Show for live reports and images during the storm.
|Credits & Contacts
Author: Dr. Tony Phillips
Responsible NASA official: John M. Horack
|Production Editor: Dr. Tony Phillips
Curator: Bryan Walls
Media Relations: Steve Roy
|The Science and Technology Directorate at NASA's Marshall Space Flight Center sponsors the Science@NASA web sites. The mission of Science@NASA is to help the public understand how exciting NASA research is and to help NASA scientists fulfill their outreach responsibilities.|
Track the ISS: J-Pass (Science@NASA); Heavens Above (external site); SkyWatch (NASA)
A helpful hint: Web sites like Heavens Abovenegative magnitudes. The astronomical brightness scale works like this: A 1st magnitude star is bright. A -1st magnitude star is much brighter. The more negative the better. The magnitude of the Sun, for example, is -26. try looking for the ISS anytime its magnitude is less than zero.
What makes the ISS shine? There are no bright lights on the outside of the space station. The ISS shines by reflecting sunlight, as much as 90% of the light that hits it. Much of the ship is light-colored. Even the awesome solar arrays, which must absorb sunlight to power the station, aren't completely black. Their reflectivity is near 35%.
NASA's Human Spaceflight -- (SpaceFlight.nasa.gov) Up-to-date information about the space shuttle and the International Space Station.
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