Tuesday, 5 September 2017

Fireball over British Colombia.

People across the Canadian Provinces of British Colombia, Alberta and Saskatchewan and the American States of Washington, Idaho and Montana have reported seeing a bight fireball meteor. The object was seen over British Columbia moving roughly southeast to northwest slightly before 10.15 pm local time on Monday 4 September 2017 (slightly before 5.15 am GMT on Tuesday 5 September) apparently entering the atmosphere roughly above the town of Boswell and exploding in an airburst (an explosion caused by superheating from friction with the Earth's atmosphere, which is greater than that caused by simply falling, due to the orbital momentum of the asteroid) close to Meadow Creek., a distance of about 100 km. The meteor is described as initially burning green, then orange, with people close to the termination point reporting a loud explosion.

Fireball meteor near Nelson in British Colombia on 4 September 2017. Rafael Pern/Twitter.

A fireball is defined as a meteor (shooting star) brighter than the planet Venus. These are typically caused by pieces of rock burning up in the atmosphere, but can be the result of man-made space-junk burning up on re-entry.

 Map showing areas where sightings of the meteor were reported, and the route of the object (blue arrow). American Meteor Society.

Objects of this size probably enter the Earth's atmosphere several times a year, though unless they do so over populated areas they are unlikely to be noticed. They are officially described as fireballs if they produce a light brighter than the planet Venus. It is possible, though unlikely, that this object will have produced meteorites that reached the surface (an object visible in the sky is a meteor, a rock that falls from the sky and can be physically held and examined is a meteorite), though most meteorites come from larger objects that penetrate further into the atmosphere before exploding, and therefore have a better chance of producing fragments that reach the surface.

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