Simply Science: Sunsets and the physics behind them

SAINT CLOUD, Minn. - In this week's Simply Science we tackle a viewer question. Jon Wood of Marshall is a photographer who loves snapping pictures of the sunset. He wants to know why some clouds turn color and some stay dark gray or blue when they are in relatively the same position.

To answer Jon's question we start with the basics...sunlight is made up of all the colors of the rainbow. But as that light travels from the horizon to your eyes, air molecules get in the way. The air scatters the light off its path, but blue and violet light is more effected than the oranges and reds. More of that reddish light is making it through the atmosphere, which makes the sunsets appear orange.

Summer haze can dull the colors, but pollution and wildfires can enhance them.

"If you add a bunch of dust particles in here, or smoke particles or whatever, let's say from a forest fire and so you're going to have even more of the blue subtracted and the effect of that is that the light is even redder," explains Rodney Kubesh, Professor with the Atmospheric and hydrologic department at Saint Cloud State University.

Regarding Jon's question; The color of the clouds is all about angles and shadows.

"This is something you'd especially notice after the sun's gone down," says Kubesh. "The sun's below the horizon. For lower clouds, this will all be shadow here. They're not illuminated so often times they look dark. Sometimes like a dark purple. The higher clouds, up here, they are illuminated by this reddened light."

Keep your questions coming by emailing Laura at or sending a message via Twitter or Facebook.


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