Are rainbows actually full circles?

Yes. Every rainbow is a full circle of light around the point directly opposite the Sun. From the ground the horizon cuts it off, so we usually see an arc; from a plane or a drone above the rain the whole circle can appear.

What's actually true

Every rainbow is really a full circle. Sunlight bounces inside raindrops at a fixed angle, so the colours always form a ring around the point directly opposite the Sun. From the ground, the land cuts the ring off, so you usually see an arc. From a plane or a drone high above the rain, you can sometimes see the whole circle.

Takeaway: Window seat on a rainy-day flight? Look for a complete circular rainbow.

Why people believe it

We think rainbows are arches because that is all we ever see from the ground, and because drawings, flags and emoji have shown them as arcs for as long as we can remember. The bottom half is missing only because there are no lit raindrops below the horizon in the right position. Lift the viewer high enough, as on a flight, and the ground no longer blocks the lower part of the ring.

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