Radial streaks
Aside from the phenomenon Carter described, one of her images also caught my attention because it captured an uncommon occurrence — a “rainbow wheel” or “spoked bow” — one that I have yet to see myself. Let’s look closely at this rare sight.
In her close-up shot of the primary bow, Carter recorded dark and light radial streaks like the spokes of a wheel descending from the primary toward the rainbow center.
“The darker spokes are produced by small clouds outside the rainbow and nearer the Sun that cast long shadows across the sky,” explains Les Cowley, a retired physicist and an expert in atmospheric optics (
www.atoptics.co.uk). “Their shadows are normally invisible, but when they block sunlight from reaching rainbow-forming raindrops, we see them as dark spokes. The spokes can be even more dramatic when seen in real life or on video, for they sometimes rotate around the rainbow, turning it into a wheel.”
Paying attention to the sky, even in the daytime, can yield views of rare events like wheels spinning in the sky. While we are all familiar with regular, single rainbows, different weather and atmospheric conditions make the variants of this phenomenon fascinating to observe.
As always, let me know what you see and think at
someara@interpac.net.