ATLANTA, United States (CNN) — Images and videos emerging from the American Northeast Wednesday look like scenes from the movie Mad Max.

The air is a horrible shade of orange and visibility is low. Distant buildings that you can see on a clear day are obscured by a dark fog.

But why does the sky appear orange and not white or gray or any other color?

Wildfire smoke turns the air orange for the same reason that clean air turns the sky blue—it has to do with the type and number of fine particles in the air and the wavelengths they block.

Sunlight has all the colors of the rainbow. When passing through the Earth’s atmosphere, sunlight hits all the molecules in the air.

The colors we eventually see are the wavelengths left after interacting with those particles. Wildfire smoke blocks short wavelengths like yellow, green, and blue—only red and orange pass through.

This effect is most pronounced in the morning and evening when the sun is low in the sky. Light has more atmosphere to pass through before reaching our eyes, which amplifies the colors and affects how thick the smoke appears in the air.

Thick smoke clouded parts of the northeastern United States, particularly New York, and air travel was disrupted in Canada as 414 fires were reported, 239 of which were out of control, Emergency Preparedness Minister Bill Blair said.