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.
See also...
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