An "unusual" reddish sky and red-looking sun have been reported across many parts of England.
The phenomenon was initially seen in the west of England and Wales before spreading to other areas.
BBC weather presenter Simon King said it was due to the remnants of Hurricane Ophelia dragging in tropical air and dust from the Sahara.
He added that debris from forest fires in Portugal and Spain was also playing a part.
The dust has caused shorter wavelength blue light to be scattered, making it appear red.
He said: "Ophelia originated in the Azores where it was a hurricane and as it tracked its way northwards it dragged in tropical air from the Sahara."
This meant dust from the Sahara was brought with it, he said.
"The dust gets picked up into the air and goes high up into the atmosphere, and that dust has been dragged high up in the atmosphere above the UK," Mr King explained.
The particles in the air cause blue light to scatter, leaving longer-wavelength red light to shine through.
The Met Office said the "vast majority" of the dust was as a result of forest fires in Iberia, which have sent debris into the air and that has been dragged north by Ophelia.
Meanwhile, hundreds took to Twitter to share their theories and snaps of the unusual red sun and yellow skies.
Using the hashtags #redsun and #ophelia, pictures were posted with earnest tags insisting that: "There is NO colour correction on this image".
As the skies turned beige over London, Hugh Bennett wondered if: "This is what it must have been like living in the olden days when everything was sepia", while James McNicholas blamed "the hipsters" for putting "an Instagram filter" on the city.
'Freaking us out'
But trending alongside #redsun, #yellowsky and #orangesky was the hashtag #apocalypse.
Like many Ben Shephard posted that: "Not messing around this light is really freaking us out!", while Henry Tudor, said: "This weird light is very disturbing. I keep expecting four blokes on horses to home galloping out of the sky."
Elliot Wagland said: "I just looked out of the window and it appears the world is about to end", and Archer Hampson said: "Somebody said we should head outside because the world was ending. We thought we'd take our cameras."
Louise Lucas, meanwhile, wanted to know if she had missed the memo "about going home early due to #apocalypse?!" and Anthony Court posted that: "If the world does end -please could it be before 10pm tonight when I start my nightshift."
But not everyone was spooked, some were inspired to write poetry like @Scott_W88, who wrote: "Ophelia, you're breaking the sun, You're shaking my garden fence daily".
While Helen Glew, said simply: "The most amazing thing is just how much of the UK is actually seeing the sun on a single October morning."