A brilliant bright light seen streaking in the night sky over the southwestern United States was most likely a fireball _ a fragment of an asteroid that entered Earth's atmosphere, a NASA scientist said.

Residents from Phoenix to Las Vegas to Southern California's coastal areas reported to local authorities and media outlets Wednesday that they saw the light move quickly from west to east at around 7:45 p.m. PDT Wednesday (0245 GMT Thursday). Many reported the light as bluish-green and others as yellow and orange. Some captured video of the object.

"We can't say 100 percent," said Don Yeomans, manager of NASA's Near-Earth Object Program, "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."

The bluish-green color suggests the object had some magnesium or nickel in it, Yeomans said. Orange is usually an indication it's entering earth's atmosphere at several miles per second, a moderate rate of speed.

"They make an impressive show for such a small object," Yeomans said.

Yeomans said fireball events are much more rare than shooting stars, but they happen on a weekly basis somewhere on Earth, usually over the ocean.

"It's a natural phenomenon and nothing to be concerned about," Yeomans said.

Federal Aviation Administration spokesman Ian Gregor confirmed that there were no aircraft incidents reported in the Western region.