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Why Colorado’s wildfires are causing those spectacular sunsets

It's all about the smoke scattering the sun's rays

A smokey sunset over the Flatirons on Aug. 12, 2020 in Boulder.
A smokey sunset over the Flatirons on Aug. 12, 2020 in Boulder.

With wildfires raging across the state over the past two weeks, Coloradans may have noticed an interesting side effect: The sunsets have been particularly colorful.

So what’s going on?

It’s a similar phenomenon to rainbows, said Robert Koopmeiners, a meteorologist with the National Weather Service in Boulder.

As the fires spew particulate matter into the atmosphere, the sun’s incoming shortwaves scatter, sending out those bright colors, Koopmeiners said — kind of like how light hits water droplets to form a rainbow.

“As the sun gets lower in the horizon, it’s got all that distance of atmosphere to come through,” he said. And that atmosphere is full of ash and burned carbon, giving it ample opportunity to scatter those waves — with red and orange being especially pronounced due to their longer wavelengths.

The atmosphere is so clogged with particulate matter that it has led people to look at the sun for far longer than is normally possible — though experts warn that this is still not a good idea.

Koopmeiners has been with the National Weather Service since the late 1980s and has seen plenty of fires hit the state.

“I’ve never seen anything like this,” he said of the recent sunsets.

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