The space shuttle Discovery will streak like a star over Maryland this weekend, making a rare appearance in this area as it circles the Earth farther north than usual on an eight-day "star wars" research mission.
If skies are clear just before dawn on both Sunday and Monday, the shuttle will be visible to the naked eye for approximately two minutes as a bright star rising swiftly from low on the horizon to a vanishing point well up in the early morning sky.
"The shuttle is one of those space marvels you usually only see on television and think of as being so remote," said Jim O'Leary of the Maryland Science Center. "But, for a couple of mornings, you can actually see it, floating there over your head."
He advises Sunday observers to find dark areas with a clear view of the southwestern horizon. Standing with their backs to the reddening glow of dawn in the east, as they look straight ahead they will see the "star" appear slightly to their left and rise over their left shoulders.
On Monday morning, weather permitting, it will appear nearly straight in front of them, in the west-southwest, and rise to a vanishing point above their right shoulders.
"It won't be as bright as Jupiter or Venus, but it should look like one of the bright, naked-eye stars," Mr. O'Leary said. The glow is caused by sunlight reflecting from the shuttle, which is traveling at 17,500 miles an hour 160 miles above the Earth.
Viewing opportunities are rare in the Baltimore area because most shuttles are launched at an angle to the equator of 28.5 degrees, ideal for putting shuttle-borne satellites into stationary orbits some 23,000 miles high, said George Diller, a spokesman for the National Aeronautics and Space Administration at the Kennedy Space Center in Cape Canaveral, Fla.
That normal orbital angle confines the shuttle to passing over a fairly narrow band of Earth's surface no farther north than Cape Canaveral, too far away to be visible from Baltimore.
But the current Department of Defense flight was launched at an angle of 57 degrees, into a wide-ranging orbit that carries Discovery as far north as Moscow and as far south as the southern tip of South America.
The space agency says the unusual orbit was necessary to get as close as possible to the Earth's poles, where the auroras -- the shimmering Northern and Southern Lights -- are being observed by test instruments for the Strategic Defense Initiative, known as "star wars."
If the shuttle sightings this weekend go bust, disappointed area residents can view another man-made space object on four early mornings beginning May 25, when the Hubble Space Telescope makes its next regular appearance.
Ray Villard, spokesman for the Space Telescope Science Institute, said Hubble could be spotted moving from southwest to southeast between 4:48 a.m. and 4:54 a.m. May 25 at a maximum elevation of 16 degrees above the southern horizon.
About a year ago, the Hubble Space Telescope was launched with a seriously flawed main mirror, but it's still the "best optical telescope" in existence, said Dr. Edward Weiler, NASA's program scientist for the $2 billion observatory.