A brilliant bright light seen bolting across the Southwestern U.S. sky Wednesday night was most likely a fragment of an asteroid that entered Earth's atmosphere, a NASA scientist said.

Experts said a fireball - or very bright meteor - was likely to blame when residents from Phoenix to Las Vegas to Southern California' coastal area reported that they saw the light move quickly from west to east at around 7:45 p.m. PT, about 10:45 p.m. ET.

I saw something that looked like a falling star, but it must have been a fireball in the atmosphere, one witness told NBCLA. It was huge. It had a green glow in front of it and a white tail. It looked like green fireworks going across the sky.

But others reported the light as yellow or orange, instead of blue or green. Don Yeomans, manager of NASA's Near-Earth Object Program, had an explanation: The bluish-green color suggests the object had some magnesium or nickel in it. And orange is usually an indication that it is entering Earth's atmosphere at several miles per second, a moderate rate of speed, he said..

 We can't say 100 percent, Yeomans said, but it's almost certain that the object was a fireball or very bright meteor, the size of a basketball or baseball that likely disintegrated before it hit the ground.

According to experts a meteor is slower than a regular shooting star, and it's not unusual for it to appear to change colors.

Fireball events are much rarer than shooting stars, but happen on a weekly basis on Earth, typically over the ocean, Yeomans said..

It's a natural phenomenon and nothing to be concerned about, Yeomans said. But they make an impressive show for such a small object.

Ed Krupp, the director of the Griffith Park Observatory in Los Angeles, said witnesses were probably seeing a piece of interplanetary debris that passed through the Earth's atmosphere and burned up, MSNBC reported.

Two known meteor showers are active this week, the Iota Cassiopeiids and the Epsilon Perseids, which peaked on Sept. 12 and 10, respectively, the American Meteor Society reported. Bright moonlight, however, is supposed to shadow the viewing of all of them, except for the brightest of them all.