British stargazers braved the autumn chill on Wednesday evening to take in the spectacular green flare of the northern lights over the night sky.
A common sight over the Arctic, northern Canada, Scandinavia and Russia, the aurora borealis is rarely seen over the UK but was this time spotted as far south as Devon, with the Met Office attributing the phenomenon to a “coronal mass ejection” from the sun.
These explosions of hot plasma on the surface of the star expel billion-tonne clouds of electrically-charged solar particles, which travel millions of miles through space at speeds of 2 million miles per hour and can collide with the Earth’s magnetosphere, subsequently accelerating down towards our globe’s north and south poles.
“These particles then slam into atoms and molecules in the Earth’s atmosphere and essentially heat them up,” explains astronomer Tom Kerss.
“We call this physical process ‘excitation’, but it’s very much like heating a gas and making it glow.”
What results is a spectacular geomagnetic storm, the aurora’s distinctive waves and “curtains” of light caused by the lines of force within the Earth’s magnetic field, its lowest point typically above 80 miles from the ground and its upper reach towering thousands of miles into space.
The heating that takes place with the collision causes the primary gases in our atmosphere, oxygen and nitrogen, to react by giving off the eerie greens, blues, pinks and yellows we observe.
“We sometimes see a wonderful scarlet red colour, and this is caused by very high altitude oxygen interacting with solar particles,” adds Mr Kerss.
“This only occurs when the aurora is particularly energetic.”
But these light flares playing out across our northern skies are usually only visible at higher latitudes, close to the poles.
A particularly strong reaction might be visible further south, dependent on cloud cover and light pollution levels in the air.
But, in truth, Scotland again had the best of it.
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