Sunday, 1 November 2015

Fireball over northern Europe.

Eyewitnesses across much of northern Europe reported seeing a bright fireball in the sky moving southwest to northeast at about 6.05 pm GMT on Saturday 31 October 2015. The event was seen from the Netherlands, Germany, Denmark, southern Sweden, northern Austria, the Czech Republic and Poland. 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. On this occasion the object ended its visible journey over western Poland, when it probably fragmented several tens of kilometers above the ground. The bright lights seen in fireballs are caused by airbursts in which rocky meteorites explode due to friction induced heating high in the atmosphere, and any fragments reaching the ground usually do so several minutes later. On this occasion Anton Norup Sørensen of the Niels Bohr Institute in Copenhagen estimates that the visible fireball occurred between 70 and 80 km above the ground.

The 31 October 2015 fireball meteorite seen from Poland. Powiat Suski 24.

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.

Map showing areas where sightings of the meteorite were reported. American Meteor Society.

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