Earth

How to see a full circle rainbow

Full circle rainbow was captured over Cottesloe Beach near Perth, Australia in 2013 by Colin Leonhardt of Birdseye View Photography. He was in a helicopter flying between a setting sun and a downpour. Used with permission. Order prints of this photo.

When sunlight and raindrops combine to make a rainbow, they can make a whole circle of light in the sky. But it’s a very rare sight. Sky conditions have to be just right for this, and even if they are, the bottom part of a full-circle rainbow is usually blocked by your horizon. That’s why we see rainbows not as circles, but as arcs across our sky.

When you see a rainbow, notice the height of the sun. It helps determine how much of an arc you’ll see. The lower the sun, the higher the top of the rainbow. If you could get up high enough, you’d see that some rainbows continue below the horizon seen from closer to sea-level. Mountain climbers sometimes see more of a full-circle rainbow, though even a high mountain isn’t high enough to show you the whole circle.

Pilots do sometimes report seeing genuine full-circle rainbows. They’d be tough to see out the small windows we passengers look through, but pilots have a much better view from up front.

By the way, we searched for images of full-circle rainbows. But most of the ones we found weren’t really rainbows. They were either halos around the sun – or airplane glories.

What’s NOT a rainbow? Hear from a master of sky optics

In this photo, the shadow of the photographer’s head – bottom, center – marks the center of the rainbow circle. This double rainbow was captured in Wrangell-St. Elias National Park, Alaska. Photo via Eric Rolph at Wikimedia Commons.

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Bottom line: Can you ever see a full-circle rainbow in the sky? Yes, but they’re most often seen by pilots, who have a good view of the sky from the wide front windows of a plane.

Posted 
August 2, 2018
 in 
Earth

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