Sun spokes are a weather phenomenon that happens when the parallel shadows from clouds are visible opposite the sun and appear to converge due to perspective, and these converging shadows coincide with a rainbow, that naturally forms in the same position in the sky (opposite the sun). The shadows on the water droplets that are causing the rainbow affect the intensity of the rainbow where these shadows fall. The whole effect is to make it look as if the rainbow has radial spokes like a wheel with bright segments of colour on the arc where the shadows do not fall. The spokes can even appear to rotate as the shadows move due to the moving clouds. I was blessed to see this phenomenon for the first time. Natural cropped photo, and contrast enhanced version to illustrate the effect more strongly, are shown below. The colour range that the iPhone 6 camera could capture is not as good as the human eye, so much colour detail is lost.
The Bible has some beautiful words about the rainbow:
Genesis 9:13-16 (KJV)