ARCTIC AURORA WATCH: A stream of solar wind flowing from a southern hole in the sun's atmosphere could graze Earth's magnetic field on Sept. 17th. Arctic sky watchers should be alert for auroras mixed with gibbous moonlight when the gaseous material arrives. Aurora alerts: SMS Text.

THIS IS NOT A NUCLEAR EXPLOSION: Fortunately, not everything is as it seems. In San Francisco, CA, Friday the 13th ended with a mushroom cloud on the horizon. It was not a nuclear explosion. "It was a sunset mirage," explains Mila Zinkova, who photographed the phenomenon:

"Friday the 13th was a hot, calm day in San Francisco," says Zinkova. "The horizon was relatively clear and we could see mirages of ships and distant lands from the beach. This made me decide to film the sunset."

Good decision. Warm air, strong temperature gradients, and at least one temperature inversion sliced the image of the setting sun into multiple distorted layers. Briefly, the sun assumed the form of a mushroom cloud, followed by an astonishing rectangular sun. But the best was yet to come.

"The sunset ended with a high green flash," says Zinkova.

This was rare indeed. Most green flashes occur right at the sea surface. This one, however, was suspended high above waters. A strong kink in the temperature gradient thousands of feet above sea level magnified usually small differences in refraction between red and green light, creating a "floating green flash."

"The last miraged image of the sun melted into the sunset sky more than 2 minutes after the predicted time of sunset, which shows how strong and anomalous the refraction was," says Zinkova. "If there were no atmospheric extinction, I probably would have been able to see the miraged sun for another few minutes." Zinkova's full video of the event may be found here.

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THE SPACE PEARL: It's the first pearl in the stratosphere. On Aug. 19, 2019, the students of Earth to Sky Calculus launched a cosmic ray balloon to the edge of space, 104,002 ft high. This sterling silver pearl necklace went along for the ride:

You can have it for $169.95. The students are selling these pearls to support their cosmic ray ballooning program. Each cultured "space pearl" comes with greeting card showing the necklace in flight and telling the story of its journey to the edge of space and back again. These make great birthday and Christmas gifts.

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