Wildfire Smoke Blows Into US

“Red sky at night, sailor’s delight. Red sky in morning, sailor’s warning," as the old saying goes. But what about glowing, hazy red skies at both sunrise and sunset? They could be a sign of poor air quality from wildfire smoke.

Smoke from wildfires often creates eye-catching red sunsets and sunrises. But how?

To understand this, we must first start by understanding why the sky is blue. The blue color of the sky is caused by the scattering of sunlight off the molecules in the atmosphere, called Rayleigh scattering.

Weather in your inbox

Forecast Location

Sign Up

By signing up you agree to the Terms & Privacy Policy. Unsubscribe at any time.

(MORE: Satellite Spots A Cloud You May Have Never Heard Of)

Rayleigh scattering causes shorter wavelengths (such as blue) to scatter more strongly than longer wavelengths (such as orange and red). The scattered light is what we see with our eyes, which is why the sky is blue.

But when the sun sets, the light from the sun must pass through more of the atmosphere, so much of the blue light gets scattered away to the point where we see only the longer wavelengths, causing the orange and red colors we see at sunset.

Now, when there is smoke in the atmosphere, these orange and red colors enhance. Since smoke particles are larger than air molecules, they cause longer wavelengths to scatter even more. So, when the sun sets on a smoky day, we will see even more red and orange colors fill the sky.

Miriam Guthrie graduated from the Georgia Institute of Technology with an undergraduate degree in Atmospheric and Oceanic Sciences and is now a meteorology intern with weather.com before returning to school for her masters.