We’ve all come to know the classic image of a rainbow as a multi-colored arch extending across the sky. Sometimes we only see half an arch. But just like the fairytales we read that often feature rainbows, the idea that a rainbow is an arch is not the truth. Read on to find out what shape rainbows actually are.
When we see a rainbow from our perspective here on earth, we perceive an arch or semicircle. However, that is not the actual shape of a rainbow. Rainbows are actually a circle.
There is a very simple reason we don’t see the full circle of a rainbow – the horizon line of the Earth cuts off the lower half.
How much of an arch we see depends on the proximity of the sun to the horizon line. The closer the sun is to horizon line, the more of the circle we will see.
However, during the sunset, a full semicircle (still not a full circle) of a rainbow can be visible. This is where the height of the sun in the sky plays a role. The higher the sun is in the sky, we see less of the rainbow above the horizon. Likewise, the lower the sun is in the sky, as at sunset, then more of the rainbow will be visible above the horizon.
There’s one way you may be able to see the full circle – you’ll have to be high enough in the sky in an airplane.