What were those bright lights in the Denver sky last night? A UFO? Richard Heene’s latest weather balloon? No and, thankfully, no. But an argument is raging over whether they came from the International Space Station or a group of Longmont skydivers floating into Invesco Field at Mile High for the Monday Night Football game.

9News received a flood of calls after some viewers said they saw a sparkling ball of fire ripping through the dark, clear evening. University of Colorado Astronomy professor Doug Duncan offered a guess: It was probably the International Space Station, and his astronomy class just happened to be on the lookout for it last night.

But members of the Denver Broncos’ Thunderstorm skydiving team later claimed their pyrotechnics probably caused the bright lights. That seems likely, given the descriptions.

But if you want to take a look at the International Space Station—just to be sure—it will fly over Denver again later this week. To find out exactly when it will pass over your zip code, visit the Fiske Planetarium or the fly-by site.