Nighttime fireball observed over the city of Groningen in 2009 ( NASA )

Bill Cooke, head of NASA’s Meteoroid Environment Office, initially reported the sighting was a brilliant fireball from a meteor burning up as it entered the Earth’s atmosphere. Later, he bowed to other expert’s opinion that it was a jet contrail reflecting the glow of the setting sun - apparently based on erroneous footage (of an actual contrail) aired by a local TV station.

This week, though, the sightings were officially reinstated as, in fact, a rare fireball - at least one yard across - bright enough to be seen during daylight.

A fireball is a meteor larger and brighter than normal. The American Meteor Society offers more background:

Fireballs occur every day over all parts of the Earth. It is rare though for an individual to see more than one or two per lifetime as they can also occur during the day (when the blinding sun can obscure them), or on a cloudy night, or over the ocean where there is no one to witness them. Observing during one of the major annual meteor showers can increase your chance of seeing another bright meteor.

Only two daylight fireballs are sighted per year on average. Coincidently or otherwise, on the same day as the San Antonio fireball, the average was tied by a daytime fireball observed over New Zealand.

For unknown reasons, fireballs visible in the night sky (at least as brilliant as Venus) occur most frequently from February through the spring. To date, at least 10 nighttime fireballs have been confirmed over the U.S. this year.

Here’s a video of one captured from University of Wisconsin-Madison on the roof of the Atmospheric, Oceanic & Space Sciences Building on Wednesday around 8:20 p.m. central time.

The American Meteor Society said it received nearly 40 reports of the above fireball from several Midwestern states.

Reports of many different colors have been received, with blue and green being most mentioned. The average brightness reported by witnesses was near the light produced by a half-illuminated moon.

This fireball streaked above the skies of the Windy City. WLS 890AM Chicago reported: “The meteor that blazed across the sky in the Chicago area Wednesday night was probably about the size of a basketball and moving about 36,000 mph.”

The last time a fireball was spotted in the Chicago skies was March 2003 WLS said.

Related links:

Texas Fireball was Real After All, NASA Says

Daylight Texas fireball was real

The Fireballs of February

Spring is Fireball Season

NASA All Sky Fireball Network Watches the Skies

Jason Samenow contributed to this post