Rainbows are normally red, yellow, green and blue–in short, all the colors of a rainbow. But the towering rainbow Jan Koeman photographed from Kloetinge, the Netherlands, on Feb. 18th was simply red:

    

“I have never seen such a rainbow before,” says Koeman. “It appeared just a few minutes after a red sunrise.”

What made the rainbow red? It was only color available. All of the other colors of the rainbow had been scattered away by air molecules and dust particles in front of the low-hanging sun.

Koeman notes another puzzle: Rainbows require raindrops, “but it was not raining at all!” he says. Atmospheric optics expert Les Cowley thinks the raindrops were there, in the distance. “There could be rain on the horizon or virga. Virga is cloud precipitation that does not reach the ground,” says Cowley.

Red rainbows are more common than you might think. They appear with frequency at sunrise or sunset, all around the world. More examples may be found in the realtime photo gallery.