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The spectacular science behind Las Vegas' vivid sunrises and sunsets

Posted at 3:47 PM, Jan 11, 2022
and last updated 2022-01-11 23:17:22-05

LAS VEGAS (KTNV) — Bursts of red, orange, yellow, pink, purple envelope the sky for miles. Colors climb the rugged desert landscape with brilliant hues at the peak.

We here in the desert can lay claim to some of the most beautiful and vibrant sunsets in the world. Why is that, you may ask? Meteorologist Bree Guy uses some viewer pictures to help explain why.

The "why" is all about perspective. As sunlight hits the atmosphere, it’s scattered by small particles. The shorter blue wavelengths we see during the day are scattered out and replaced with longer red wavelengths at twilight.

"When the run is rising or setting, the sun is further away from us, which means it has to travel further. So it needs long wavelengths. Reds and oranges are those longer wavelengths," National Weather Service meteorologist Jenn Varian said.

The shorter the wavelength, the easier it is to scatter. When the sun is further away, those rays have to pass through a thicker level of the atmosphere and, by the time it gets to us, all the violet and blue has already been scattered, leaving vivid reds.

The sunsets with the most "wow" factor typically have clouds. That cloud layer can make or break a beautiful sunset.

"If you have a higher cloud base, you’re going to have more opportunity for the sun to reflect off the cloud," Varian said. "The lower the sun gets and the higher the cloud, you have a long wavelength hitting and a long wavelength coming down, so you’re going to get those purples and reds."

A common misconception is that low-level air pollution causes more colorful sunsets; however, that’s not quite the case. When there are a lot of these large, harder-to-scatter particles, they act as a screen and mute the colors in the sky.

The cleaner the air, the better. But Las Vegas' air quality isn’t always the best, so we also need something else. The desert wind kicks up small dust particles that are easy to scatter and move. Moisture causes particles to swell, get bigger and move more slowly. Those larger particles may be harder to scatter, but lucky for us, we have drier air for a lot of the year.

"We know that clouds make pretty sunsets, but sometimes we don’t have clouds and still have pretty sunsets," Varian said. "Part of that is because we have dust, and part of that is because we have smog. If there is a wildfire nearby and we have a little more smoke in the air than normal, you may notice that there are pretty colors through the entire gradient of the sky. Same goes if there is a lot of dust lofted."

The sunset forecast for Tuesday and Wednesday call for a spectacular sight.