BUTTE COUNTY, Calif. - On Monday, several people around the area saw a strange object in the sky. This object was seen moving very slowly East-to-West, but what was it?

There are several theories. Some believe it was a space ship while others believe it was the International Space Station.

Dr. Eric Ayars, chair of the physics department at Chico State, believes the object sighted was a weather balloon. 

The object is white, circular and semi-transparent. 

Nick Nelson, a physics professor at Chico State, does not believe it could be the International Space Station. 

"I mean it's a good guess, the International Space Station. It's the brightest satellite, simply because it is so big and it is in a very low orbit. But that same low orbit means that it moves fast. So, you wouldn't see it sit still for hours or even move slowly. You'd see it go all the way from one horizon to the other in a matter of 20-30 minutes, tops."

The International Space Station also is best seen as a small dot at dawn or dusk, similar to a very bright star in the sky. The object spotted on Monday was much larger than how a star would appear in the sky.