Wednesday 17 February 2021

Fireball over the English Channel.

Witnesses across the Netherlands, Belgium, Luxembourg, France, Germany, England, Wales and Scotland, have reported observing a bright fireball slightly at about 5.10 am local time GMT on Friday 12 February 2021. The fireball is described as having moved from east to west along the south coast of England, appearing off the coast of Folkstone and vanishing to the south of Brighton. 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 12 February 2021 fireball meteor seen through dense cloud from Ash Vale in Surry, England. Meteor News.
 
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).
 
Heat map of northwest Europe showing areas where sightings of the meteor were reported (warmer colours indicate more sightings), and the apparent path of the object (blue arrow). American Meteor Society.  
 
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.
 
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