Shades of a Multihued Arch : What Causes a Rainbow

What is a Rainbow?

Ever see a multicolored arch in the sky? The name for this phenomenon is a rainbow, A rainbow is an arch with different colors; from red to blue to purple and is one of the most common meteorological-related wonders.

But what causes a rainbow? How are they formed? How do rainbows get their colors? All of these questions will be answered throughout this article!

What Causes a Rainbow?

What Causes a Rainbow

To understand what causes a rainbow, you need to do a little experiment with a glass triangle (if you don’t have one, you can just read the steps):

√ Light is made of all sorts of colors: from bright colors like green to end of the spectrum colors like violet. Things like a prism (a flat, triangular shape that refracts light) can take light and can create a smaller version of a rainbow. Prisms are made with glass or plastic.

√ For the prism to make a small rainbow, you have to allow a small light beam on one side of it. To know how to do this, go to the physics of the rainbow website: ( This is called the dispersion of colors.

√ The dispersion of colors happens when there’s the refractive index. The refractive index is found in the glass of the prism. Once light reaches a material, there is a difference between the refractive index between air and light, causing the light to bend.

√ With all of this information out of the way, raindrops play an important part in the creation of a rainbow. They act like tiny prisms in which light enters. Light reflects off of the side of a raindrop and then it will exit. Then it will break into a spectrum and create a rainbow!

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Why are Rainbows are Curved?


Now you know what causes a rainbow, why the shape? While rainbows look two-dimensional to us, they are three-dimensional. But what makes rainbows three-dimensional?

Before going into an explanation, switch your mind to three-dimensional mode! Now let’s go back to the raindrops: the light from the sun or any light is at an angle between 40 to 42 degrees. The sun is low and is behind us.

With that being said, the raindrops with sunbeams bounce at an angle of 40 degrees. They can bounce in any direction at the 40-degree angle: up, down, or sideways.

So what happens to these raindrops? Believe or not, rainbows are round! If you look at a cone model, all of the raindrops on the surface of the cone are visible and can be close to us or could be far away from us.

The other drops that are not on the cone create rays for the colors of the rainbow, but they are not visible with the naked eye.

Causes of Color in a Rainbow

Causes of Color in a Rainbow

Now that you know what a rainbow is, what causes it, and why they are curved: you might be wondering what causes the color in a rainbow. It all has to deal with the raindrops (one of the main components for a rainbow)! As you know, the rainbow is made of all sorts of colors.

If you observe a rainbow, it all depends on the position of perception: one ray of light can reach your eye because the raindrop is dispersed. The violet ray of light is seen at 40.6 and the red ray of light is seen at 42.4, so it is higher in the sky when you look at it.

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There are about 6 different angles for raindrops. These angles are also called internal and double reflections (they’re also triple and quadruple reflections).

Now for a secondary rainbow, they are formed from double internal reflections. The light is reflected twice in a raindrop before leaving it. This light is between 50.4 and 53.6, which then forms a second rainbow above the main one.


what is rainbow

Rainbows are one of the most amazing phenomenons that you can see in the sky. There are also double rainbows: where sunlight can be reflected triple or more in times with just one raindrop! Remember if you want to memorize on how they are created: What causes a rainbow is raindrops and sunlight (or other light)!

Written by: Alicia Barton

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