How far is the rainbow from you?

Why is the rainbow always so far away from you?

If you look at a rainbow it always seems to be at the horizon, but it is actually closer to you; how come?

The rainbow is visible because light from the sun is reflected by the raindrops under a cloud at an angle of 42 degrees as shown in the picture below. The raindrops are not in a vertical plane. The rainbow is not as flat as we perceive it.

The reason why we perceive the rainbow as flat and very far away is that seeing the rainbow is actually a stereoscopic phenomena. Your two eyes each see a different rainbow! These two rainbows are horizontally apart the same distance as your eyes. You actually see a stereo pair of rainbows and because you look parallel at them, the rainbow appears to be far away (at the horizon).

Now look parallel at the stereo pair pictures below.

Next time you take a picture of the rainbow, take two pictures from two positions about 10 to 20 centimeters horizontally apart and then view your photos as a stereo pair.