Circular rainbows

Where do bad rainbows go?

To prism. It’s a light sentence,

but it gives them time to reflect.

image by nick sidle

30,000 ft above. “If you glance out the windows on the right side of the plane, you might catch sight of a circular rainbow suspended in the clouds. That ring of light reveals the true shape of a phenomenon we think we know so well.”

These circular rainbows form when sunlight passes through countless tiny raindrops. The light bends as it enters, reflects off the droplet’s inner surface, and then bends again as it exits. Each hue unfurls into the spectral display that we call a rainbow.

So why do we usually see only an arc from the ground? The Earth blocks the lower half, leaving us that familiar curve. But from a plane or a mountain top, the full circle appears—because you can see the entire cone of refracted light. Without the Earth in the way, every rainbow would blaze as a brilliant, spinning halo in the sky.

(Thank you, to my fabulous friend, Sandy, for letting me know about circular rainbows!)