Thursday 14 September 2017

Fireball meteor over Iceland.

Witnesses have reported seeing a bright fireball meteor across much of Iceland on Tuesday 12 September 2017. The Astronomical Society of Seltjarnarnes has received witness reports from the Northwestern, Northeastern, Southern and Capital Regions, all reporting a bright object slightly before 10.50 pm. Based upon these accounts they estimate that an object a few centimetres across entered the atmosphere at a speed of about 20 km per hour (slow for a meteor, suggesting that it was moving around the Sun in roughly the same direction as the Earth before it was caught by our gravity), and exploded 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) more than 20 km above the ground.

Meteor over Iceland on 12 September 2017. Stjörnufræðivefurinn.

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.

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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