The skies above Oregon turned an apocalyptic shade of red yesterday like a scene straight out of Blade Runner 2049. Although this year's events might make you wonder whether the rapture is upon us, these scarlet-soaked skies are actually a consequence of the wildfires that are currently raging along the west coast of America. 

Dozens of people took to social media to share the unusual views of their hometowns in Oregon yesterday. Remarkably, many of these photographs were taken long before sunset during full daylight hours despite the sky looking ominously dark. 

The coloration is because of the wildfires ripping through Oregon (and California and Washington), but the red skies are not directly due to the glow of the flames themselves. It’s the result of a phenomenon called Rayleigh scattering caused by smoke particles from the wildfire.

Rayleigh scattering explains why we see the sky as blue during daylight and reddish-pink skies during sunset or sunrise. Visible light is made up of all the colors of the rainbow – red, orange, yellow, green, blue, indigo, and violet – in different wavelengths, from short wavelengths (such as blues) to the high frequencies (reds).

As sunlight passes through the many gases and particles in Earth’s atmosphere, the different wavelengths get broken up through refraction and scattering. This scattering is more effective at short wavelengths towards the blue end of the visible spectrum (to be picky, pure air actually scatters violet more effectively than other wavelengths, but human eyes are more sensitive to blue light).

During daylight, this effect causes sunlight to be lightly scattered and appear blue. At sunrise or sunset, the Sun is lower in the sky and takes a much longer path through the atmosphere, so more scattering occurs and the sky appears redder. More light can also be scattered if there’s more pollution, smoke, and other micro-particles in the atmosphere, such as those from the wildfires right now. A very similar phenomenon occurred last year in Indonesia in the wake of massive forest fires in the area. 

Meanwhile, the wildfires continue to blaze. There’s been much media attention on the wildfires in California, but there are equally shocking fires occurring in neighboring states Oregan and Washington too. 

The National Weather Service placed northwest and southwestern Oregon under an extreme fire danger warning on Tuesday, September 8, the first time southern Oregon has faced such a warning. That same day, Oregon Governor Kate Brown also declared emergencies for numerous blazes across the state, describing the situation as “a once-in-a-generation event.”

“Wind continues to fuel the wildfires, with devastating consequences across Oregon. People’s homes, lives & land are at risk,” Brown tweeted. “If you are in an evacuation area, please pay close attention & listen to local calls to evacuate — this can save your life & the lives of our firefighters.”