Ever wonder? 3.1

Q: Why are rainbows round?
Q: Why are rainbows round?

A: You see a rainbow when the sky in front of you is full of raindrops, and the sun is at your back. The parallel rays from the sun pass over your head and strike the raindrops, which act like little prisms.

As a ray of light enters the drop, it is broken into its constituent colors – red, orange, yellow, green, blue and violet.

Each of these colored rays then strikes the back wall of the raindrop, and is reflected back toward the front.

These reflected, colored rays leave the raindrop at a certain angle, and they can be seen only when they enter the eye at that same angle; just as a small object can be seen in a tiny mirror only when the viewer moves so that the object’s reflected image enters the eye at a certain angle.

Therefore, in order to see the colored rays reflected out of a single raindrop, the eye, the sun and the raindrop must be at one specific angle.

And to see the reflected rays coming from millions of raindrops, this angle of reflection must be exactly the same for each drop.

Now if you were asked to arrange several million raindrops so that the angle between the sun, the drop and the viewer’s eye was always the same, you would find that you had to arrange the drops in a circle.

To see this, imagine a cone placed flat-end down in a drinking glass.

Note that the angle between the sides of the cone and the sides of the glass remain the same only because the cone is circular.

Any change in the shape of the cone would clearly change the angle.

In this analogy, the sides of the glass represent the parallel rays of the sun, the bottom rim of the glass represents the field of raindrops, the sides of the cone are the reflected rays of colored light, and the tip of the cone is the viewer’s eye.

– Douglas B. Smith

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