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What a fantastic rainbow!

Yesterday evening there was a particularly great natural spectacle in Jena. Even the view to the west towards the sunset was fantastic:

Ok, it looks like an atom bomb went off somewhere in Weimar. But the city still stands and it was “just” an extremely spectacular sunset. But it got really fantastic when you turned your back on the sunset and looked to the east. Then there was a rainbow to be seen. And what a one! It was the most spectacular I've ever seen. Huge and wide and the colors as strong as if they were painted directly on the sky with wall paint. A sight at the one of the mouth remained open and could be not really stick with a camera (at least not when one of photography has so little idea how). But I tried it anyway:

Well, like I said before. No comparison with the original. You can't even see the secondary rainbow really well. Fortunately, there were some other Jena and Jenensians who took better photos:

ScienceBlog colleague Anke took this picture:

Sebastian Grabert took a particularly fantastic picture:

And here is another great recording by Uta von Förster:

Oh, you should have seen that live, it was really all a lot more impressive, even if the photos are cool! On them you can also see a few properties of the rainbow that you don't see that often. The secondary rainbow, for example, or “Alexander's dark ribbon” (the area between the two arches that looks darker than the area inside the main rainbow). Fortunately, all of this can be explained. In contrast to John Keats, who complains in a poem about the evil scientists who dare to explain the rainbow and take away its magic:

“Do not all charms fly

At the mere touch of cold philosophy?

There was an awful rainbow once in heaven:

We know her woof, her texture; she is given

In the dull catalog of common things.

Philosophy wants to clip on Angel’s wings,

Conquer all mysteries by rule and line,

Empty the haunted air, and gnomed mine–

Unweave a rainbow, as it erewhile made. "

I think of Richard Feynman, who said that an explanation of things can never destroy the existing beauty. “There is always only beauty added”he said, and of course he's right. So! Let's see how a rainbow is created. Because that's more complicated than you might think. Sure, the rainbow is created by the light of the sun that is refracted in the drops like in a prism. Every child learns that much at school. But the details are known and fewer people.

A rainbow, for example, is not a fixed structure that you could walk around to look at it from the side or from across the way. You can only see it when the sun is right behind you. And it only exists when you look at it. There is no rainbow without an observer. The raindrops fall to the ground and are constantly in motion. The drops that ensure that we see a rainbow are never the same but are constantly alternating. The sunlight hits the drops and is reflected back as a cone of colored light at an angle of about 42 degrees.

Ray path in the raindrop

Each raindrop reflects and refracts the light, creating all the colors of the rainbow. But we only see the rays of light that hit our eyes and because differently colored light is refracted to different degrees, we see the typical sequence of colors in the rainbow:

Yesterday evening there was a particularly great natural spectacle in Jena. Even the view to the west towards the sunset was fantastic: Picture: @ n4d1n1 Ok, that looks like ...