From Myth to Reality: Photos Prove Triple Rainbows Exist

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Angela Stark
The Optical Society
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From Myth to Reality: Photos Prove Triple Rainbows Exist

Single rainbows are inspiring, double rainbows are rare, but tertiary rainbows have been elusive until a meteorologist provided guidelines that showed how to find them

WASHINGTON, Oct. 5—Few people have ever claimed to see three rainbows arcing through the sky at once. In fact, scientific reports of these phenomena, called tertiary rainbows, were so rare—only five in 250 years—that until now many scientists believed sightings were as fanciful as Leprechaun’s gold at a rainbow's end. These legendary optical rarities, caused by three reflections of each light ray within a raindrop, have finally been confirmed, thanks to photographic perseverance and a new meteorological model that provides the scientific underpinnings to find them. The work is described in a series of papers in a special issue published this week in the Optical Society’s (OSA) journal Applied Optics.

In addition to the confirmed photo of a tertiary rainbow, the optical treasure hunt went one step further, as revealed in another photo that shows the shimmering trace of a fourth (quaternary) rainbow.

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(a) Original image of a third-order (tertiary) rainbow. The image was taken May 15, 2011, in Kampfelbach, Germany and is the first-ever picture of a tertiary rainbow. Two reference positions (A and B) for image orientation are indicated. (b) Processed version of image (a) after contrast expansion and unsharp masking, showing a rainbow-like pattern next to the image center, marked by the arrows. Credit: Michael Grossmann/Applied Optics.

The third-order (tertiary) rainbow (left), accompanied by the fourth-order (quaternary) rainbow (right). They appear on the sunward side of the sky, at approximately 40° and 45°, respectively, from the Sun. This is the first picture ever of a quaternary rainbow in nature and the second picture ever of a tertiary rainbow. Credit: Michael Theusner/Applied Optics