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The Physics of Fire Rainbows


Sometimes clouds color with the hues of a rainbow: green, blue, faint red. Some other times, fire rainbows set them ablaze.

Rainbows are a relatively easy to observe, provided that cloud formations are right and we are paying enough attention. But there is also the more unique version of this phenomenon. It is called a fire rainbow, and it looks like a colored flame or a phoenix in mid flight. What causes this stunning phenomenon?

The physics is actually very simple. Fire rainbows are produced when sunlight enters a special kind of cloud formation at a specific angle. They are almost always seen on cirrus clouds, which are characterized by their thin, wispy strands. Sunlight penetrates the hexagonal ice crystals that form in these clouds at high altitudes, refracts and splinters into a rainbow contained within the feathery cloud.

The perfect place to catch these creatures in flight is close to the central meridian with the sun at a 67 degree angle over the horizon. Whenever you see cirrus clouds, be sure to look up toward the sky: perhaps Nature will meet your gaze with an unforgettable spectacle of color.

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