Cynthia Crowther had just lit a cigarette outside her Newmarket home when the sky suddenly caught fire.

"Oh my God, I think I just saw a plane crash," she declared to her husband, running inside.

A ball of light, seething white, had careened overhead, spitting out dazzling debris.

She called police, the government, airport authorities.

Seeing his wife so frantic, Russell Crowther imagined worse.

"I thought it was a nuclear warhead," he recalls. "I was just squinting, waiting for us to evaporate."

At about the same time that Newmarket seemed scheduled for heavenly demolition, Scott Sweeney was driving home from his parents' house, along Wisconsin's stretch of Interstate 94. He was headed for Milwaukee on a four-lane highway flanked by fields and trees when, "something just caught my eye ... it was going straight down."

Indeed, the whitish-green fireball was on such a dramatic collision course that, from his vantage point, the 35-year-old IT technician imagined two grim scenarios: a mighty cannonball into Lake Michigan. Or Milwaukee was due for a celestial smackdown.

"I honestly waited to see something come up from the ground."

But what actually fell from the sky Sunday night, visible between 8 p.m. and 8:30 p.m. to rapt observers from here to Milwaukee, probably landed as a rock no bigger than a fist, weighing about a kilogram.

"Everything I have heard suggests that it was a bolide - a meteorite that was flaming through our atmosphere," explains Paul Delaney, a physics and astronomy professor at York University. "It probably came to ground somewhere. But where, nobody knows."

What's certain is that for three or four spine-tingling seconds, people from a massive swath of the continent shared the same slice of burning sky. And everyone imagined that whatever it was had landed in their own backyards.

"That is not at all unusual for really bright bolide," Delaney observes. "They have huge distances over which they can travel and therefore be seen."For all you know, it's up to 10 kilometres. That means its travel distance can be huge."

Fifty kilometres? Five hundred kilometres?

"It could be 5,000 kilometres, mate."

But a hurtling meteoroid glows white-hot as it rushes through the Earth's atmosphere. And, like a red-hot stick waved around at a campfire, it leaves a brief but extremely bright trail - "So it doesn't have to be very big to be seemingly really bright," Delaney says.

The North American Aerospace Defense Command certainly didn't flinch as it monitored the sky.

"We're pretty vigilant in terms of monitoring the skies," said Maj. Jason Proulx, a NORAD public affairs officer. "But what we do is we assess whether it poses a risk or a threat. If it doesn't pose a threat, it's not something we would express further interest in."

It was dramatic enough for television stations in Wisconsin to assure residents it was not a UFO. Closer to home, one radio report suggested the flaming fury landed in Nobleton, and police switchboards from around the GTA received calls from people who had seen the fireball.

If anyone does manage to find this heavenly visitor, the earthly rewards could be substantial. Museums may pay as much as $3,000 for a meteoroid of that size, Delaney estimates.

"These are wonderful laboratories," Delaney says. "It's a piece of space.

"Some of the rocks that come to ground are literally leftover pieces from the solar system's formation. All of a sudden, we step back in time 4 1/2 billion years ago, to the way the solar system was at that moment in time."

To the untrained eye, a meteorite would look like just about any other rock. Hence, a farmer plows over it. Or a road is built. Bye-bye, mystery.

"Unless somebody saw it hit," Delaney says. "The chances of us finding it are really slim, unfortunately."