By Thomas Miller
Dr. Alan Hildebrand, an associate professor at the University of Calgary, tracked the fireball that lit up the sky in Lloydminster on Feb. 21.
Hildebrand has been investigating fireballs for nearly 20 years and is co-ordinator of the Canadian Fireball Reporting Centre.
He said what we saw on Feb. 21 was an “exceptional case,” estimating the size of the rock at more than 100 kilograms.
“We would have about 100 meteorites fall in Canada each year,” said Hildebrand. “Even a relatively small fireball could drop one meteorite. That one Tuesday night is big enough that it probably dropped hundreds. Something like it would happen somewhere on the earth, let’s say once a week or so.
“That’s just the way our solar system is made – the number of asteroids we have in the asteroid belt, the rate at which material leaks out into earth-crossing orbits, that determines the frequency of these.”
Hildebrand said the speed of the rock, which was travelling at about 20 kilometres per second in the air, produced the light we saw above Lloydminster.
“You’ve got all that kinetic energy to scrub off,” he explained. “The fireball is a rock decelerating in the atmosphere. Once something is going faster than three or four kilometres per second in the air, it’s going fast enough to make a shockwave and produce light. So all that energy gets scrubbed off with a big light show.”
On an astronomical scale that is used to compare light – called V magnitude – he said the fireball was brighter than -15, which is brighter than a full moon.
“We get these all-sky cameras, so of course I compare the brightness as recorded on those cameras to brightness of other fireballs over the years,” Hildebrand said. “I compare, frankly, the impression that it makes on people. If it’s bright enough, people are more excited about it.
“I look at how much it lights up the sky. Witnesses say, ‘It lit up the ground around me,’ that means it’s getting quite bright. Security cameras show that this one lit up the ground very much so.”
Hildebrand uses the brightness of the rock to determine its size.
Simply enough: The brighter it is, the bigger it is.
And if the meteor is bright enough, that’s where the term fireball comes from.
The fireball appeared over our skies at approximately 8:40 p.m. on Feb. 21.
Because of witness reports in the Battlefords and Rockhaven, Hildebrand thinks the fireball landed somewhere southwest of North Battleford.