SEATTLE -- A warm, sunny summer Sunday in Seattle ended with a show as the sunset put on a brilliant display of what is known as crepuscular rays.
The colorful photo from Seattle photographer Sigma Sreedharan shows what appears like heavenly beacons emanating from the Olympic Mountains on the horizon.
In reality, they are just a shadowy effect.
"Crepuscular rays are simply long shadows cast by clouds, mountains, or other objects that block the light of the sun," Michael Kavulich, an associate scientist with the National Center for Atmospheric Research, tells FOX Weather. "We don't often notice (except for *very* hazy days), but even on clear days a little bit of sunlight is getting scattered by pollen, dust, smoke, and pollution. In this way we can see the ‘clear’ air as slightly brighter than the same air that wasn't illuminated by the sun."
The shadows run in parallel lines to each other, but since the Earth is a sphere, the shadows instead appear to the eye to converge on where the sun is setting. Think of how train tracks point toward the horizon. The tracks run parallel to each other all the time but appear to converge to a point on the horizon.
The crepuscular rays do the same thing.
"After sunset this phenomenon can be most pronounced due to the glow of the red sunset light contrasting with the dark blue night skies seen through the shadows – that's what has caused the shadows in the photo (above) to look so amazing," Kavulich said. He thinks the mountains on the horizon were the shadow culprits in the photo. I'd have to check the satellite archives to be sure; as you can see in the link above, they are often visible quite strikingly from space!
And under certain conditions, the effect can appear on the opposite side of the sky too, where those same shadows appear to converge once again to a point on the horizon.
In this case, the point would be exactly opposite of where the sun sits on the other horizon -- known as the anti-solar point. Those rays, appropriately enough, are known as "anti-crepuscular rays."
But if you were to flatten the sky out instead of a sphere, you would just see straight parallel lines of shadow streaking across the sky.
"At sunset these shadows could stretch over 1000 miles long!" Kavulich says.
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