Main Facts on Rainbows

The Rainbow is described best by Author Donald Ahrens, when he stated a rainbow as being "one of the most spectacular light shows observed on earth".

The sun is always behind you when you face a rainbow, and the center of the arc of that rainbow is in the direction opposite to that of the sun. Yet the rain, of course, is in the direction of the rainbow.

We don't see a full circle of rainbow, because the earth blocks it. The lower the sun is to the horizon, the more of the rainbow we can see. Sunset we see the most, a full semicircle of the rainbow with the arch 42 degrees above the horizon. The higher the sun goes up in the sky, the smaller the arch is above the horizon.

The primary rainbow forms between about 40 and 42 from the antisolar point. The light path involves refraction and a single reflection inside the water droplet. If the drops are large, 1 millimeter or more in diameter, red, green, and violet are bright but there is little blue. As the droplets get smaller, red weakens. In fine mist, all colors except violet may disappear. Even finer fog droplets, smaller than 0.05 mm, produce the white rainbow or fog bow.

Rainbows are not seen in midday since the whole 42 circle is below the horizon at most latitudes. So rainbows tend to be seen most in the later afternoon when a thundershower has passed and the sun from the west is shining on the receding edge of a raincloud moving east. It is possible to see the entire circle of the rainbow from an airplane since there can be falling droplets both above and below you.

The single (original) rainbow is known as the "primary rainbow". It always has the color red on the outside (top) of the bow, and the color violet on the inside (bottom) of the bow.

The primary rainbow always appears lower in the sky, morning or evening.

You can never be directly under a rainbow.

No two people can ever see the same rainbow. As the eyes of two people cannot occupy the same place in space at the same time, each observer sees a different rainbow. Why? Well, because the raindrops are constantly in motion so its appearance is always changing. Each time you see a rainbow, it is unique from all the others. In fact, each eye sees its own rainbow!

Some rainbows have faint arcs just inside and near the top of the primary bow, known as supernumerary arcs.

The sky is brighter inside the rainbow due to the rainbow ray.

If you were to look at a rainbow with polaroid sunglasses and rotate the lenses around the line of sight, part of the rainbow would disappear! Interesting!



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About Rainbows

What is a Rainbow?


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What Makes the Bow?

What Makes Up the Colors of the Rainbow?

Primary Rainbows

Double Rainbows

Reflection Rainbows

Lunar Reflections


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P. Beauchamp: Pebeauch@nmu.edu