Image from Shelby Hogan. The dark sky between the primary and secondary rainbows is called Alexanders Dark Band.

We had some nice storms rumble through North Alabama this evening and, just at sunset, the storms passed Huntsville. I expected to receive some rainbow pics and I was not disappointed! A double rainbow is reversed, of course, from the primary but in between the sky will look a little darker. You can see it clearly in the picture on the right.

This was first described by Alexander of Aphrodisias around 200 CE.  Alexander is famous for his many commentaries on the works of Aristotle, who lived over 500 years before. You can read more about it on Les Cowley’s excellent atmospheric optics site here.