Blood rainbow

At dusk or dawn, you might someday see an all-red rainbow.

Bloodbow / CC BY

The blood rainbow represents a rare intersection between two of this blog’s obsessions: rare meteorological phenomena (the darkness between rainbows; endless lightning; moon rings) and blood (Antarctic blood falls; blood type personality; blood rain). As much as I would like to report that a blood rainbow comes from blood rain, the truth is more prosaic.

At sunrise and sunset the light is often pinkish or reddish. This is because the sun’s rays are taking the long route through the Earth’s atmosphere. Rather than coming in from overhead, the light is effectively travelling sideways through the atmosphere, and that means that most of the shorter wavelengths bounce off air and airborne particles – leaving mostly or only the longer wavelength of the colour red. That’s also why sunrises and sunsets are more impressive during dust storms, forest fires, and volcanic eruptions.

On the rare occasion that a rainbow is formed at that time of day, it contains much more red light than any other kind. The result: a beautiful blood-red bow. An impressive one appeared in Calgary nearly two weeks ago (see the link below).

[Thanks to Gareth E. for suggesting this topic.]


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