Scientists aren't sure what exactly lit up the sky Wednesday night -- but at least they can agree on one thing: it wasn't a UFO.
A possible asteroid, described as a "fiery ball across the sky," was seen by residents in Phoenix, Los Angeles and here in San Diego.
Many have speculated that the fiery ball may have been a small asteroid.
A NASA spokesperson said that's most likely what it was. The spokesperson said it was the size of a basketball or baseball.
SDSU Astronomy Professor Paul Etzel said he believes it may have been a piece of debris that had fallen off a man-made satalite in space, and burned in the earth's atmosphere.
“The type that was seen last night is actually quite common, but what made it unusual was the time of night and the fact that it was seen over populated areas,” Etzel said.
Etzel said most of the time meteors come in traveling the opposite direction of the earth’s rotation causing them to burn up more quickly.
This one however traveled in from West to East, the same direction as the earth meaning it took longer for it to burn up, and therefore the glow lasted several seconds.
He said the green color is how oxygen looks when burning in the upper levels of the atmosphere.
Those who managed to see the burning object at about 8 p.m. Wednesday night noticed its slow speed and green glow.
"I saw it [Wednesday] night while walking my dog. I thought it was a firework in the neighborhood. Seemed slower than a shooting star," said Dustin Froehlich on Twitter.