Why is the sun red? Hurricane Ophelia causes rare weather phenomenon

Colin Cradock took a photo of a red sun in Oldland Common in South Gloucestershire.

Colin Cradock

There was an eerie red glow hovering over England on Monday as the sun turned blood red while the remnants of Hurricane Ophelia slammed into the country.

Meteorologists say the unusual phenomenon was caused by strong winds pulling up dust from the Sahara. The dust particles in the air caused shorter wavelength blue light to scatter, allowing longer wavelength red light to shine through.

"As [Ophelia] tracked its way northwards it dragged in tropical air from the Sahara," BBC News meteorologist Simon King reports. "The dust gets picked up into the air and goes high up into the atmosphere ... above the U.K."

Debris and smoke from wildfires in Portugal and west-central Spain may also be contributing to the red hue, King says. A prolonged drought and mid-October temperatures of more than 86°F has led to the increase in late-season fires.

The Met Office, the U.K.'s national weather service, said winds from Ophelia will also bring warmth to the area. Temperatures across large parts of southern and eastern England are expected to exceed 68°F on Monday, with isolated spots reaching up to 75°F — about 18°F higher than the average high for October.

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The National Oceanography Centre shares a photo of a red sun caused by red Saharan dust.

Twitter/@NOCnews

Research charity Asthma UK warned Monday that dust and particles in the air could trigger asthma attacks, urging those with severe asthma to stay indoors.

"Everyone with asthma must make sure they take their reliever inhaler (usually blue) everywhere with them and continue to manage their asthma with their preventer inhaler (usually brown)," the charity wrote in an online statement.

But the Met Office said the air is safe to breathe, as the particles are high up in the atmosphere.

In fact, a red sunset happens in a similar way when dust scatters the light.

"A red sky appears when dust and small particles are trapped in the atmosphere by high pressure," the Met Office explains. "This scatters blue light and leaving only red light to give the sky its notable appearance. A red sky at sunset means high pressure is moving in from the west so therefore the next day will usually be dry and pleasant."

The red Saharan dust may not have much of an impact on the U.K., but it does impact oceans, the National Oceanography Centre announced on Twitter.

The iron that gives Saharan dust its red color acts like fertilizer, which is needed for growth of microscopic plants that tiny sea creatures, like zooplankton, feed on.

"There is no doubt that the supply of dust from the Sahara radically alters the structure of plankton communities and enhances the downward flux of organic material into the deep ocean," Professor Richard Lampitt of the National Oceanography Centre said in a 2014 article.

While the bright red sun was initially seen in England, the phenomenon soon reported in other areas — like France.

Viewers were quick to share photos and videos of the rare sight on social media: