The Rainbow Connection

The Rainbow Connection

What is a rainbow?When the sunlight begins to shine behind you at the end of a rainstorm, you see the light of the sun reflected in the water droplets, just like a prism.  The ray of light, or rainbow ray, enters one side of the water droplet, bending a little (refracting), bounces off the curved back of the droplet, and is refracted again as is emerges from the other side of the droplet, making the bow shape.

We see different colors because each raindrop reflects the light differently. We see the color red at 42 degrees, and blue at 40 degrees. Each raindrop is viewed at a different angle, creating the colors. This is a primary rainbow. When the energy from the light enters the raindrop a second time, it is reflected at a higher angle: red at 50 degrees and blue at 53 degrees. This produces a secondary, or double, rainbow, which has the colors reversed.

Very little light is reflected higher than the rainbow ray, but a lot of light is reflected by the many rays emerging from the water droplet, so the sky appears brighter inside the rainbow.

When more than one ray of light enters a raindrop, the interference in the path of the reflection and refraction can cause additional arcs above or below the primary rainbow. These are known as supernumerary arcs.

At the angle of the rainbow ray, unpolarized sunlight is almost completely polarized. If you were to view the rainbow through polarized eyeglasses, part of the rainbow would disappear.

Sometimes the sunlight is reflected off water or some other surface. This produces a reflected rainbow higher in the sky than a rainbow produced directly from the sun.

A full moon is also bright enough to refract light, but the lunar rainbow is not nearly as bright as one produced by the sun’s rays.