Remember the over-the-top, borderline-insane glee of "double rainbow guy"? Well, imagine how excited he'd be if he saw a triple rainbow. Only five tertiary rainbows — the scientific term for three rainbows arcing through the sky at once — have been spotted in the last 250 years; others have been dismissed by the scientific community as hoaxes. But now, using new findings published in the Optical Society's journal Applied Optics as their guide, scientists are embarking on a treasure hunt for the elusive phenomenon. Who are these rainbow chasers? Here's what you should know:
First off, how do rainbows work?
When sunlight hits raindrops at a relatively low angle, the colors within the light bend and reflect at different angles — separating the colors and creating the optical effect of a rainbow. A double rainbow occurs when not all of that light exits the drop, and is instead reflected back into the raindrop to go through the process again. As a result, double rainbows are dimmer, because the amount of original light is split and diminished in the re-reflecting process. That same principle applies to tertiary rainbows, which are even dimmer and more difficult to see.
Why the renewed interest in triple rainbows?
Credit the U.S. Naval Academy's Raymond Lee. At a recent meteorological conference, he presented a computer model explaining the conditions in which triple rainbows are most likely to be seen: "Dark thunderclouds and a heavy downpour with uniformly sized droplets," says Duncan Geere at Wired. "In these conditions, if the sun breaks through the clouds, a tertiary rainbow can be created that's visible." Lee challenged the attendees to go out and find triple rainbows, and photographer Michael Thusner eventually caught one on camera.
And this photo is real?
It seems like it. And if it is, the photo corroborates Lee's claim that not only are triple rainbows possible, but quadruple (or quaternary) rainbows could theoretically be seen, too. What's the best way to lay your eyes on these "incredibly rare" lightshows? Geere says, "Next time you're in a storm and a double rainbow appears, turn around and look towards the sun."