Ask Ellen: What caused this sunset edge?

GRAND RAPIDS, Mich. (WOOD) — Spectacular things can happen in the sky during sunrise and sunset, including what one viewer spotted on his trip to Tennessee.

Gregg Blohm said he was on a sunset boat ride on Tim Ford’s lake when a distinctive line split across the sky.

“It didn’t have a color variation in it and it disappeared as the sun went down,” Blohm said.

The phenomenon appeared just 20 minutes before the sun had completely set.

So what is happening here? The answer is surprisingly easy! The sky’s distinct line and color change is simply the difference between light and shadow. Further west in the distance, a large thunderstorm anvil has grown tall enough to cast a shadow as the sun sank low on the horizon.

A shadow like this can be cast more than 100 miles away, creating the illusion of a split sky across a wide landscape. This also explains why the line disappeared the moment the sun sank below the horizon. A shadow will disappear once a light source leaves.

Anvil shadows aren’t overly common, but they are not considered rare. Typically they are spotted more frequently in climates favoring more thunderstorm days, which makes sense. More anvil clouds in general increase the chances of anvil shadows.

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