Low-tech camera helps track fireball

The sun had just gone down on one of those great, warm January days we'd been having. Lyn Stol made his way down Main Street to the Broadway Market, a grocery store in downtown Blackfalds, 130 km south of Edmonton. Stol and his friend Gord Leibel, who manages the store, stood in the alley for a smoke. Their conversation was interrupted when a fireball streaked across the sky.

"We were standing there having a smoke, with the door opened, and all of a sudden I looked up and saw this great big star fly by," recalled Stol, a 73-year-old retired carpenter. Before Leibel could poke his head around the door, the show was over.

"It sparkled, you know, on the back, and then all of a sudden it went out."

Stol isn't the only person who saw the Jan. 25 fireball. Volunteers who run the rooftop observatory at the University of Alberta's physics building saw the meteor (a bright streak of light) as well. And more importantly, a camera designed to track extraterrestrial objects recorded the meteoroid (interplanetary debris) as it entered the atmosphere.

The fireball's trajectory was videotaped not only by the U of A camera, but also by others in Edmonton and Sherwood Park. Martin Connors at Athabasca University and Allan Hildebrand at the University of Calgary are analyzing information from the tapes to determine a potential fall zone for this meteoroid.

Physics professor Doug Hube cups his hands and guesses that when the meteoroid entered the atmosphere, "it probably could have comfortably fit in one or two hands." The meteoroid would have been travelling at speeds of up to 60 kilometres per second, heating the air around it to produce a brilliant white glow as bright as a quarter moon. With telephone and e-mail reports of the fireball pouring in, Hube wrote to newspapers in central Alberta, asking their readers to contact him. Spectacular as the fireball was to the naked eye, the cameras delivered a more reliable account, he adds.

"Eyewitness reports of things in the sky, or automobile accidents, are not always completely reliable because they happen so quickly and are unexpected," said Hube.

Most witnesses failed to report a so-called terminal burst, in which the meteoroid shatters as forces of severe heat on its surface and extreme cold in its core collide.

"It's quite common for these things, near the end of a visible event, to blow apart."

Videotape from the all-sky cameras is considered the final authority. The cameras, on loan from Sandia Labs in New Mexico, record images of the sky 24 hours a day. The Jan. 25 fireball is the first such event recorded since the cameras began operating in May.S

The all-sky camera is essentially security camera mounted above a hemispherical mirror. The mirror expands the camera's peripheral sight, giving it the same sort of view you get through an apartment-door peephole. Jason Hessels, a physics undergraduate student, spent last summer calibrating the U of A camera and writing a computer program that translates an object's position on the mirror to its position in the sky.

"In theory, if you have a good enough idea what the trajectory is in atmosphere, you can extract it backwards and find out where it came from," said Hessels. Though final calculations are not in, Hube says meteorite fragments may have landed southeast of Stettler, 180 km southeast of Edmonton.

How would anyone know a meteorite from any other rock on the ground? Freshly fallen meteorites have a distinct black crust, but over time most become "a nondescript grey" colour. Others, called metallic meteoroids, are easier to spot. Made of 95 per cent iron and nickel (the same elements comprising the Earth's core), the rocks are "unusually heavy" for their size. It's important that such interplanetary debris is tracked down and studied, Hube says, because it can teach us about the larger environment we live in.

"They are the building blocks of the planets," he said. "They can give us clues about circumstances in this corner of the universe 4.5 billion years ago.

Stol's still willing to talk. "If you come on down for a coffee," he offers, "I'll tell you all about it."

Video of the fireball can be seen at www.phys.ualberta.ca/video.meteor.html.