Rainbow Spokes

June 10, 2004


Provided by: Shannon L. Story, StoryLine Ink
Summary authors & editors: Shannon L. Story

We had bad some nasty storms here in North Texas on the last day of April, 2004. The above photo was taken about 45 minutes before sunset. After the weather settled down a bit, I went outside to see what kind of damage we received from the high winds and hail. In the western sky, the Sun was peeking through the holes in the clouds. I turned to the east and saw that a rainbow was visible. In addition, there was also something else I had never seen before. From the east (and to the left of the rainbow), this beacon of light was streaming upward. How could light be streaming from the eastern horizon?

As a result of perspective, shadows in the sky appear to converge toward the antisolar point (opposite the Sun), which is also where rainbows occur. If clouds or even heavy rain obscure the sunlight, which contributes to the forming a rainbow, then the "shadowed" raindrops are no longer able to direct the rainbow's ray toward your eyes. This can lead to the formation of one and sometimes several dark radial spokes, centered on the antisolar point. When this happens, the rainbow may resemble a wagon wheel. For more about this see Les Cowley's "Atmospheric Optics" link below.

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