Tonight's scheduled launch of the space shuttle Endeavour, weather permitting, may be visible to viewers along the East Coast of the U.S.—also weather permitting.

If the skies are clear, the shuttle's engines should burn bright enough to show up during its initial climb. Joe Rao of the Hayden Planetarium in New York City blogs: "For most locations, Endeavour ... should appear as a very bright, pulsating, fast-moving star, shining with a yellowish-orange glow."

Rao advises that shuttle-gazers in the Southeast U.S. look toward Cape Canaveral, midway down Florida's Atlantic coast; that those in the mid-Atlantic look southwest three to six minutes after liftoff (scheduled for 7:55 P.M. in the East); and that those in the Northeast look low along the horizon to the south or south-southwest, six to eight minutes after takeoff.

Unless you're very close to the launch site, the shuttle will be low in the sky, about 5 to 10 degrees, Rao writes. "To get an idea of how high this is," he says, "make a fist and hold it out at arm's length. Place the bottom of your fist on the horizon; the top of your fist is 10 degrees."

The weather looks to be reasonably amenable to a launch, with the National Weather Service reporting a 30 percent chance of rain tonight at Kennedy Space Center as of 5:45 P.M. Spotting the shuttle may be dicier: forecasts for launch time project isolated thunderstorms in Charleston, S.C., showers in Washington, D.C., and clouds in New York City and Boston.

If there's a patch of clear sky in your area, you may want to take this chance to try to see Endeavour: the future of the shuttle program is in doubt beyond 2010, meaning that only nine more launches may remain.