According to the Met Office, the red sun is caused by winds pulling up Saharan dust.
This dust is then reflected and refracted in longer wavelengths, giving a red appearance to the sky. This dust scatters the blue light from the sun letting more red light through much as at sunrise or sunset.
Some areas have been forced to turn on street lights in the middle of the day as the dust partially blocked out the sun.
Smoke from wildfires occurring over northern Iberia has also been pulled up high up into the atmosphere by ex hurricane Ophelia.
Some aircraft flying at altitude have reported a smell of burning in the cabin which reinforces this theory.
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