September 20 - propeller of light

Sometimes there is this amazing effect when the sunset is partially blocked by a cloud on the horizon. The clouds create shadows across the sky, and the sunlit clouds look like a giant airplane propeller.

This is the view of the actual sunset.

This is the sky in the opposite direction as the sunset-lit stripes move across the sky to the horizon.

This is a closer view of part of the illuminated striations. the light seems to spill out of the cloud.