Aug. 4, 2019: Over the weekend in DeSoto, Kansas, something strange happened to the sunset: It turned purple. “On Saturday night, I photographed a large dome of pinkish-purple light,” reports Doug Zubenel. “Strong crepuscular rays were also visible.”

Photo credit: Doug Zubenel of DeSoto, Kansas. August 3, 2019.

Purple sunsets are a sign of volcanic activity. Fine volcanic aerosols in the stratosphere scatter blue light which, when mixed with ordinary sunset red, produces a violet hue.

But which volcano? The answer is probably Raikoke, a volcano in the Kuril islands which erupted with such force on June 22, 2019, that it was seen from the International Space Station. NASA satellites confirm that aerosols from Raikoke reached the stratosphere and they have been circulating around the Northern Hemisphere ever since.

A similar eruption occurred 11 years ago, in Aug. 2008, when Alaska’s Kasatochi volcano spewed sulfurous gases into the stratosphere. For months sky watchers witnessed strange sunsets whenever a plume of Kasatochi’s emissions drifted overhead. The same thing, apparently, is happening now thanks to Raikoke.

Photo credit: Heiko Ulbricht in the Zittau Mountains of southeastern Germany. July 26, 2019.

Volcanic sunsets have also been seen in Halifax, Nova Scotia; in the Zittau Mountains of Germany; in Joshua Tree, California; in Orange, California.

Purple isn’t the only thing to look for, says atmospheric optics expert Les Cowley. In addition, he advises, sky watchers should “be alert for a very bright yellow twilight arch, fine cloud structure in the arch seen through binoculars, and long diffuse rays and shadows.”

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