Aurora Rainbow
Taken by Alan C Tough on April 18, 2021 @
Hopeman, Moray, Scotland
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Camera Used: Canon Canon EOS 5D Mark III
Exposure Time: 20/1
Aperture: f/3.2
ISO: 3200
Date Taken: 2021:04:21 21:43:34
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Details:
A wide range of colours are revealed in this auroral display:
Green shading to red above is caused by the excitation of Oxygen atoms at a height above 100 km.
The purple colouration at the top is the result of an enhancement of the emission from ionized Nitrogen molecules when they are exposed to sunlight or bright moonlight. Look up 'resonance scattering'.
If the incoming particle beam has sufficient energy to penetrate the atmosphere to below 100 km, excitation of Nitrogen and Oxygen molecules produces a red lower border.
The yellow colour is due to the intensity of the display and is a mix of the green and red emissions.
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