Our friend Karl Diefenderfer in Quakertown, Pennsylvania, captured this image on May 10, 2019, around 6:15 p.m. He wrote:
Rainbow spokes are always a treat …
Les Cowley, at the great website Atmospheric Optics, offers this explanation for rainbow spokes:
Shadows in the sky appear by perspective effects to converge towards the antisolar point, which is also the center of rainbows. When clouds or dense rain showers shadow the light falling into your rainbow cone the shadowed raindrops can no longer send the rainbow’s rays towards your eye. The result is one or more dark radial spokes centered on the antisolar point and making the rainbow sometimes resemble a wagon wheel. Bright spokes are similar to anticrepuscular rays except that light is directed into specific directions by large raindrops rather than widely scattered by dust and aerosols.
Sometimes, when clouds are moving fast across the sky, the rainbow wheel appears to rotate.
The brightness of the unshadowed areas illustrate nicely just how much of a rainbow’s light is cast inside its rim at deviations larger than the minimum of the rainbow angle.
Thank you, Karl and Les!
Bottom line: Photo of rainbow spokes.
Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.