Just after 9:35 tonight, step outside, find a clearing in the sky, face south and wait for a rare light show, courtesy of NASA.

If the weather cooperates in Florida, and the clouds stay away from the coast -- as the National Weather Service is forecasting -- you'll be able to see the space shuttle Discovery leave a fiery streak across the night sky.

There are engineering and safety calculations behind tonight's blastoff, the first night launch in four years. But once the shuttle Discovery's three main engines light, it's all about the "wow" factor.

"When you see it, you won't be mistaken," said Ralph Horvath, president of Sun City Sky Watchers, a group of astronomy enthusiasts in Myrtle Beach, S.C. "It makes a huge streak of light from the south, and the shuttle leaves a big fire trailingbehind it. You can't miss it."

On Wednesday, NASA monitored discouraging weather forecasts but otherwise declared shuttle Discovery ready for blastoff.

During the 12-day flight, commander Mark Polansky and his crew will deliver a new component to the International Space Station, rewire the station's electrical system and ferry a new crew member to the station.

Want to watch?

WHEN TO LOOK: According to the space.com Web site, if the shuttle launches on schedule at 9:36 p.m., it should be closest to Raleigh about six minutes later. So you can watch the launch on TV, then start scanning the sky to the southeast.

HOW TO WATCH IT: The shuttle will be about 10 degrees above the horizon. Hold your arm straight in front of you. Make a fist. Put the bottom of the fist on the horizon. The top of your fist is about 10 degrees above the horizon.

BEST VIEWING: The shuttle might be tough to see from most wooded neighborhoods. But open fields, bluffs and tall buildings with views to the southeast should work.

WHAT YOU WILL SEE: Discovery will seem to "flicker," then abruptly wink out 8 minutes and 23 seconds after launch as the main engines shut-down and the huge, orange, external tank is jettisoned over the Atlantic at a point about 870 statute miles northeast of Cape Canaveral.

A POSTPONEMENT? If the launch is scrubbed today, the next possibility is Friday at 9:13 p.m. Could make for a great cheap Friday night date.