No, it's not the apocalypse.

Things looked a bit eerie in the United Kingdom on Monday, as the afternoon skies turned an unusual shade of red. Experts say the former Hurricane Ophelia is to blame for the rusty overcast and red sun in the U.K.

Central London Red Sun
Credit: Dominic Lipinski/PA Images via Getty Images

The storm’s powerful winds carried with it dust from the Sahara desert, as well as smoke from the wildfires in Portugal and Spain, according to Chris Dolce, a digital meteorologist at The Weather Channel.

“The glowing red and orange skies are due to Rayleigh scattering,” Dolce told Travel + Leisure.

This is when “smoke particles act as a filter for sunlight,” Dolce explained. Debris in the air scatters short, blue wavelengths of light, leaving only longer wavelengths of the spectrum — like red and orange.

The effect is a dusky, subdued red light.

Of course, this isn’t the only time the sky has turned red. As Dolce pointed out, the effect is common at sunrise and sunset: “Since the sun is at a lower angle in the sky ... light has to pass through more of the atmosphere, including, in this case, smoke and dust particles.”

Smog and clouds can also affect the color of the sky.

Other Theories About the Red Sky Over the U.K.

Despite the consensus from meteorologists and other weather experts, some people have developed a number of other theories about why the sky over the United Kingdom has turned red. TIME pointed out that social media was particularly doom and gloom about the red skies.

An apocalypse, a zombie apocalypse, a “Star Wars”-style invasion, and a new Instagram filter seem to be the winning hypotheses.