The UK Meteor Observation Network has received reports of a bright fireball meteor being seen over much of the UK and parts of Ireland slightly after 5.30 pm GMT on Sunday 31 December 2017. The fireball has been described as being greenish in colour, which may indicate it was caused by the explosion of a small meteorite with a high iron or magnesium content, and was seen across most of England, as well as southern and eastern Scotland and parts of Ireland. 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.
The 31 December 2017 northern England meteor. American Meteor Society.
The object was seen moving from east to west over northern England, apparently entering the atmosphere somewhere over the North Sea 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) above Carlisle.
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. The brightness of a meteor is caused by friction with the Earth's atmosphere, which is typically far greater than that caused by simple falling, due to the initial trajectory of the object. Such objects typically eventually explode in an airburst called by the friction, causing them to vanish as an luminous object. However this is not the end of the story as such explosions result in the production of a number of smaller objects, which fall to the ground under the influence of gravity (which does not cause the luminescence associated with friction-induced heating).
The 31 December 2017 northern England meteor seen from East Barnet in North London. Jim Rowe/UK Meteor Network.
These 'dark objects' do not continue along the path of the original bolide, but neither do they fall directly to the ground, but rather follow a course determined by the atmospheric currents (winds) through which the objects pass. Scientists are able to calculate potential trajectories for hypothetical dark objects derived from meteors using data from weather monitoring services.
Witness reports can help astronomers to understand these events. If you witness a fireball-type meteor over the UK you can report it to the UK Meteor Observation Network here.
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