A large and brilliant flash of moving light accompanied by a trail of smoke and seen high in the sky across a wide swath of eastern North America on Monday evening, July 23, was most likely an asteroid that exploded during a fiery plunge through Earth's atmosphere, scientists say.

The early evening fireball was seen as far north as Toronto and as far south as southern Virginia. Scientists at the American Meteor Society (AMS), who monitor such events, now suspect the event was centered in the skies above Pennsylvania.

Law enforcement offices across the East were flooded with calls around 6:18 p.m. EDT Monday by people who reported seeing a multicolored fireball that lasted a second or more. Some witnesses also heard a sonic boom associated with the flash.

"Based upon a preliminary review of the data, this appears to be a single fireball event," said Jim Richardson of the AMS. "The sonic booms were generated as the fireball reached lower altitudes, below about 20 miles, and continued to decelerate."

Pilots over Pennsylvania, Delaware and Maryland reported the spectacle to federal aviation officials.

An analysis of accounts indicates that the fireball moved from East to West. It was sighted from New York City to western Pennsylvania. It is not entirely clear if all witness saw the same object or if there might have been multiple fireballs created when an original rock broke apart.

"As far as we can determine, there was only one event," Richardson told SPACE.com.

Though it was broad daylight, the fireball was described variously as being as bright as the full Moon or even the setting Sun. Others said it looked like an airplane on fire. And pick your color: Some saw orange and yellow. Others described it more patriotically as a white object with a red tail and blue flashes.

Richardson called it "one of the bigger fireballs for this year, over North America."

He said many such events occur worldwide each year, but the timing and location of this one made it conspicuous. "What makes this event noteworthy is that it occurred over heavily populated areas, during the summer, when people were outside, and in the early evening rush hour."

Earlier news reports had suggested the fireball was associated with a meteor shower, but this is unlikely. Meteor showers involve a rain of small debris -- typically objects no larger than a grain of sand -- left behind by a comet that swung through the inner solar system but did not threaten Earth.

In fact, one of these events is underway now. The annual Perseid meteor shower began in mid-July and is currently building toward a peak in August. While Perseid meteors are known for their trails of smoke or dust, they are not known for producing fireballs as dramatic as the one spotted earlier this week.

Nor was the event likely responsible for a scorched cornfield in Salladasburg, Pennsylvania, west of Williamsport, as was reported by CNN and ABCNEWS.com. In fact, there are no confirmed reports of any meteorites from the event. A meteorite is a meteor or asteroid fragment that reaches the ground.

"While Salladasburg is in the area where the view of the fireball was perhaps the best, ... our preliminary analysis indicates that the fireball probably passed East to West over the Welsboro/Morris Pennsylvania areas, which are slightly north of Salladasburg," Richardson said. "Any potential meteorites from this fireball would have fallen further to the west of all of these towns."

Richardson also notes that fireballs that do generate meteorites stop emitting light when they are still about 9-12 miles high. They are usually "not red-hot when they reach the ground."

Fire in the sky

Several witnesses reported their observations to an Internet mailing list called "MeteorObs," which tracks meteors and fireballs. Donald Kehne of Deale, Maryland described it this way:

"It had a distinct teardrop shape and long brilliant tail," Kehne reported. "It appeared in the northern sky ... and streaked downward in a westward arc, lasting 3-5 seconds before it disappeared from view behind a nearby tree line to the west-northwest."

Another viewer, Tony Cecce, said, "My mother was outside, she didn't see the meteor itself but did see the landscape briefly brighten then heard two sharp booms. The booms were quite unlike thunder, she thought there was a car accident."

Though fireballs like this are typically caused by relatively small asteroids, from the size of a baseball to that of a bus, there is a chance the object was a piece of a comet, which might have broken apart sometime in the past.

"At this stage, we do not know if the object that created this fireball was cometary or asteroidal in origin," Richardson said. "Nor do we have any information on size and speed as yet."

Space rocks fall through Earth's atmosphere regularly, and most pose little or no threat as they vaporize in the atmosphere, due to the intense heat created by friction as they speed Earthward at thousands of miles per hour.

Some do fall to Earth. Some 400 tons of debris -- small rocks and dust -- rains down on Earth daily. But since the planet is about two-third's water, many fireballs and impacts are never noticed.

The Federal government, however, is listening.

Data from this week's fireball will be analyzed in upcoming weeks.

Local observers in Canada's Yukon Territory recorded one of the more memorable recent fireballs in 2000. That object was also roughly the size of a car, and fragments were discovered in the ice and later studied. The fragments were found to stink, revealing a composition that is still being examined.