This map shows areas of North America where a sounding rocket launch should be visible on Oct. 7, 2015.

Update: The NASA sounding rocket blasted off at 7:07 p.m. EDT (2307) GMT on Wednesday.

A NASA rocket launch on Wednesday (Oct. 7) should give skywatchers in the Eastern United States a real treat, weather permitting.

NASA plans to launch a sounding rocket at 7 p.m. EDT (2300 GMT) on Wednesday from the agency's Wallops Island Flight Facility in Virginia. If all goes according to plan, the liftoff will produce several multicolored patches of light in the darkening sky that will be visible to many people in the Middle Atlantic and Northeast United States. You can watch the launch live on Space.com, courtesy of NASA TV.

These conspicuous glows will be man-made features — clouds of barium vapor released by the two-stage modified Black Brant IX sounding rocket. [NASA's Amazing Small Rocket Launches of 2015 (Photos)]

The rocket will be launched on an east-southeast trajectory, reaching a maximum altitude (apogee) of 161 miles (259 kilometers) about 4.5 minutes after it leaves the launch pad at Wallops. About 6 to 6.5 minutes after the launch, on the rocket's downward leg, as many as four barium clouds will be released over the Atlantic Ocean, at altitudes of between 118 and 130 miles (190 to 209 km), over a point roughly 125 miles (200 km) downrange from Wallops.

The rocket was originally scheduled to launch this evening (Oct. 6), but bad weather forced a delay. The launch window runs through Oct. 12.

The evening of the launch depends on weather conditions at the launch site as well as the presence of clear skies for at least one of two NASA optical tracking stations. Mission updates will be noted on the Wallops launch status line at 757-824-2050.

Tracer is used to study the ionosphere

Scientists have launched vapor tracers into the upper atmosphere since the 1950s. Such research has greatly aided understanding of the planet's near-space environment, NASA officials said.

These materials — including barium — make visible the naturally occurring flows of ionized and neutral particles, either by luminescing at distinct wavelengths in the visible and infrared part of the spectrum or by scattering sunlight.

For example, a fraction of a barium cloud ionizes quickly when exposed to sunlight. As a result, the cloud can be used to track the motion of charged particles in the ionosphere, as well as the motion of neutral particles in the upper atmosphere.

A small quantity of strontium will be added to the barium mixture for Wednesday's experiment, making it easier to track the cloud, NASA officials said. [Images: Mysterious Night-Shining Clouds]

Exotic colors

Vapor clouds seemingly explode into view when first released, sometimes blooming so rapidly they resemble fuzzy fireworks.

Depending on the state of the atmosphere, these clouds may appear to expand to several times the apparent size of the moon; on other occasions, they appear to elongate in a north-south fashion or stretch out into long plumes. Initially, they may appear to glow with prismatic colors, although the primary colors are expected to trend toward bluish-green and purple-red. Since observers must be in darkness while the barium cloud is in sunlight, the technique is limited to observations near sunset, local time.

As a result, the Black Brant IX rocket has a 10-minute launch window beginning at 7 p.m. EDT, about 30 minutes past local sunset, when the sun's rays will still be coming in from the west to light the clouds at high altitudes.

Depending on atmospheric conditions, the barium clouds could persist for as little as 2 minutes. But they could linger for as long as 20 minutes before fading completely away.

UFO scares

Of course, the sudden and unexpected appearance of several multicolored clouds in the early evening sky might alarm unsuspecting people and lead to a rash of UFO reports. This has happened before.

In March 1967, for example, NASA launched sounding rockets from Wallops Island, producing an array of colored clouds in the evening sky. On March 31, 1967, The New York Times reported that the display "puzzled thousands of persons" in the New York area, and also resulted in people along the East Coast calling newspapers and police stations for an explanation of the strange sightings.

The Times also reported that one man "described the rocket residue as 'twin beams of a giant searchlight playing colors on the sky.'"

On Jan. 16, 1975, Newsday, a newspaper that serves Long Island, New York, reported a "ghostly blue-green glow that floated slowly westward" and produced a flood of phone calls to police, airports and the news media. The newspaper received almost 500 phone calls, 200 of which were logged within 15 minutes after the mysterious cloud first appeared.

"Some thought it was a flying saucer," reported Newsday, adding, "Others thought it might be a weather balloon or a Russian missile attack.

Where to look for the colored clouds

Remember that the clouds will begin to appear 6 minutes after the rocket leaves the launch pad at Wallops Island. If you live in the eastern United States, direct your attention toward the waters just offshore from Wallops.

For New Jersey, eastern New York and New England, face south or south-southwest.

For central New York, central Pennsylvania, Delaware and much of Maryland, face southeast.

For the eastern third of Virginia, face east. For the eastern third of North Carolina, face northeast.

For places farther to the west and south, the twilight sky will probably be too bright to see the clouds, as it will be too close to sunset.

As to where in the sky to look, the closer you are to Wallops Island, the higher the clouds will appear. Keep in mind that your clenched fist held at arm's length is roughly equal to 10 degrees.

At a distance of 250 miles (400 km) from Wallops, the highest of the clouds will appear 30 degrees up from the horizon.

At 500 miles (805 km), the altitude drops to 15 degrees, and at 800 miles (1,290 km), it's just 10 degrees ("one fist") up in the sky.

The launch of the Black Brant IX rocket itself might be glimpsed for up to several hundred miles from the Wallops Island launch site.

NASA's Wallops Flight Facility has a handy launch viewing guide for skywatchers here:

http://www.nasa.gov/centers/wallops/events/viewing_launches.html.

Editor's note: If you capture an amazing image NASA's rocket launch that you would like to share with Space.com and its news partners for a story or photo gallery, send photos and comments in to managing editor Tariq Malik at: spacephotos@space.com.

Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmer's Almanac and other publications, and he is also an on-camera meteorologist for News 12 Westchester, N.Y. Follow us @Spacedotcom, Facebook or Google+. Originally published on Space.com.