Rainbows

Rainbows have fascinated people for as long as there have been rainbows. But where does the rainbow actually come from? How is light fashioned so that it can create this marvelous display for us to enjoy? And why are the colors always in the same order: Red, Orange, Yellow, Green, Blue, Indigo, and Violet?

These may be some of the questions going through your mind right now, so without getting too technical, I am going to attempt to shed some light on the subject—so to speak.

Light is made up of many colors, but each color has its own frequency which causes them to travel at different speeds. Due to this variance, each color passes through refraction at a slightly different angle from the others. This alters the degree at which it passes through one medium to the next which results in the different colors splitting apart. For example, longer wavelengths are bent at longer angles, like red light which bends at a 42 degree angle when passing through a drop of rain or a glass prism, while violet light waves are shorter and bend at a 40 degree angle.

Simply put, a rainbow is refracted light which is created when white light shines through water or a glass object, which then bends the light, splitting it and separating the colors from within. This splitting apart of the white light into its basic color elements is called dispersion. Because they bend at different angles they fall slightly apart from each other, creating the rainbow effect.

When Did People Discover That White Light Was Made Up of Colors?

Sir Isaac Newton was born in England in 1642. It was during a time and place when reason and rational thought were beginning to blossom, taking the place of centuries of superstition and ignorance.

At this time it was commonly believed that when white light passed through a prism it was distorted and impurities were introduced to the light, by the prism itself, causing the colors to appear. Newton, however, did not believe this. He had a different theory, but instead of blindly believing what he thought to be a reasonable explanation, he devised and conducted an experiment to determine if his hypothesis was correct.

Newton’s theory was this: If the prism was corrupting the light with some form of impurity then the colored light would also be altered by the impurities. If, as he suspected, this was not the case, then the colored light would remain pure.

In order to test his theory Newton created a rainbow by shining white light through a prism. Behind this rainbow he placed a piece of white paper with a slit cut into it. By adjusting the rainbow on the paper he was able to isolate one color at a time, allowing only that color to shine through the slit. He placed another prism behind the paper and aimed the colored light into it to see if the prism would alter the color.

Newton found that when he shone the colored light through the second prism it remained unchanged. This proved that it was not the prism which was altering the color of the white light because it had not altered the colored light. With these results upon which to base his conclusion, Newton determined that the colored lights were already there. It was only when they were all blended together that they created the illusion of pure white light; the prism merely separated them so they could be seen individually.

A device called Newton’s wheel (which can be made from common items around the house) can give a practical display of how this works. Learn how to make your own Newton’s Disk on this video.

What About Rainbows Formed in Nature, Not the Lab?

The most common natural formation of a rainbow is made when the sun shines through rain drops. The same principles still apply, but instead of using a prism, or other type of glass to refract the light, water in the form of rain drops does the work for us.

Raindrops have a different shape and consistency than a glass prism, but they work more or less the same way. When white light from the sun strikes a collection of raindrops it must do so at a fairly low angle on the horizon in order for you to get a sharply visible rainbow, and the angle of each raindrop will affect what colors you will see. Remembering that each color of light travels at different frequencies, and splits at different angles, will help us to understand how this works.

There are six different kinds of rainbows that can form naturally, and which you might encounter in different kinds of weather conditions, with varying altitudes. Most of us have seen the standard single rainbow, which may stretch completely across the sky in a brilliant arch, or perhaps begin to fade halfway across, but there are five other kinds of rainbows which are a little less known.

• Double Rainbows

• Full Circle Rainbows

• Fog bows

• Monochrome Rainbows

• Fire Rainbows

In this video you can see what these rainbows look like and learn a little bit more about how they are formed.

Now that we understand a bit more about rainbows, you may be wondering why some rainbows form an arch and others are in a straight line. Well, it’s actually quite simple when you think about it. Rainbows which are formed in nature, are formed by light splitting through raindrops which are spherical, and the rainbow’s visibility is affected by how low the sun is on the horizon. The earth is also a sphere and as such the rainbow must curve to follow the sun’s rays along a curved line. Rainbows which are created with a prism or other kind of glass have little to no curve for the light to bend the colors through, so these rainbows are generally straight with very little curving.

Either way, whether you are having fun with a prism or gazing at the spectacular view of a rainbow from your home or favorite nature site, nature’s color palette is a wonder to behold!