Pictures: First Quadruple Rainbow Ever Caught on Camera

First Quadruple Rainbow Picture
Photograph courtesy Michael Theusner, Applied Optics
Blink and you might miss them, but these two colorful smudges (center) form the second half of the first quadruple rainbow to be caught on camera, validating years of claims that such phenomena could exist, a new study says.
"[It's as if] the natives are telling you that there's this creature in the rain forest, but they only have stories," said Raymond Lee, a professor of meteorology at the U.S. Naval Academy, who recently published a study in the journal Applied Optics describing the conditions under which a tertiary rainbow should be visible.
Lee's research inspired some scientists to try to snap photos of the elusive vision, resulting in this picture, taken June 11 near Bremerhaven, Germany. "When you finally succeed in capturing it in photography, that's a thrill," Lee said.
And while "quadruple rainbow" might call to mind a stack of four arcs, only two rainbows can be caught in a single frame, because of the way light reflects and bends within raindrops.
As a ray bounces around inside a droplet, some light escapes and is split into its constituent colors, forming a rainbow. Each time the ray gets reflected, the light, and thus the rainbow, gets a bit dimmer.
When this happens three or four times, the final rays exit in the direction of the light source—the sun—and create extremely faint rainbows opposite the original two, which can be seen only while facing away from the sun.
"[There are] a couple conditions that are conducive to forming these things. Neither one of them is very enticing for photographers or casual viewers," Lee said. "You have to have ... an absolutely inky black cloud background ... and then either a uniform distribution of raindrop sizes, or it has to be absolutely pouring."
These uncomfortable conditions may explain why triple and quadruple rainbows have been so hard to find for so long, despite having been known in theory for more than a century.
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—Rachel Kaufman
Published October 7, 2011
First Triple Rainbow Picture
Diagram courtesy Michael Grossmann, Applied Optics
The first picture of a tertiary rainbow was taken in Kampfelbach, Germany, on May 15, 2011, and required heavy image processing (right) to reveal the third arc. (The other two are behind the photographer and visible only when facing away from the sun.)
"It's not a bright rainbow. It's more a very subtle change in color," study co-author Philip Laven said of tertiary rainbows. "It's very difficult [to see]—everything has got to be just right."
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Published October 7, 2011
Double Rainbow Over Alaska
Photograph by Rich Reid, National Geographic
Rainbows, including this double rainbow over Alaska, form when sunlight is refracted, or bent, inside a raindrop, reflected by the drop, and then refracted again as it exits, so that the white light is split into its component colors. A double rainbow appears when light is reflected twice. A triple rainbow would come from thrice-reflected light, and so on.
"It's counterintuitive" to most people that the triple rainbow would be near the sun, Lee said. "People have this reasonable expectation that, I see something pretty in that direction, so all the pretty things would be in that direction.
"But there's nothing weird going on here. Just as a mirror can send light in many different directions, so can raindrops."
(Pictures: "Night Shining" Clouds Getting Brighter.")
Published October 7, 2011
Colorado Colors
Photograph by Robbie George, National Geographic
Rainbows across a dramatic backdrop, such as this Colorado landscape, may look gargantuan, but they're actually the same "size" as rainbows created when light hits the spray from a garden hose, Lee said. Those garden-hose rainbows are really just small segments of full rainbow arcs that, given the right conditions, would extend as far as the ones pictured.
"But people associate the image with whatever they see on the landscape, so the ones you see against the beautiful background" are more emotionally stirring.
In other words, rainbows are visions, but only illusions. "People get very excited by seeing a bright double rainbow, and they just project onto it their own emotions," Lee said.
"Just last weekend at the grocery store," added Lee, "I saw one of the finest double rainbows it was my luck to see in 20 years."
(Related: See a new species of "rainbow glow" jellyfish.)
Published October 7, 2011
Island Arcs
Photograph by Kenneth Garrett, National Geographic
Seen from the sky, a double rainbow seems to touch down on reefs off the Yucatán Peninsula (map).
For years rainbows have fascinated thinkers, including 17th-century French philosopher and optics scholar René Descartes, of "I think, therefore I am" fame. Descartes, a rainbow expert, was wrong about triple rainbows, though. He proclaimed that viewers should be able to see stacks of three rainbows.
"One of the fathers of rainbow science," Lee said, "got it wrong."
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Published October 7, 2011