After a spell of rain, many of us have seen rainbows in the sky. The conditions need to be perfect for us to see a rainbow.

We need some water in the air and the Sun to be behind us so we don't get wet. Light passes through water droplets to create a rainbow.

The light from the sun is white. White light is made up of different colors. These colors can be separated by a raindrop.

Waves of light

Light travels in waves like waves in the ocean. There are different colors in the rainbow.

The distance between the top of the wave and the bottom is different for each color. The visible spectrum is the wavelength from violet to red with the longest.

The raindrops look more like balls than ellipses. Light can change direction when hitting a ball of water. This is called afraction by us.

The different wavelength is reflected by a small amount. If the light hits the raindrop at the right angle, the light's wavelength is separated into its different colors. These colors are seen as a rainbow in the sky because of the amount of light that is reflected through the rain. The order of the colors is determined by how long they last.

The seven colors of the rainbow are red, orange, yellow, green, blue, and indigo. This isn't always the case.

Colors in the rainbow

It is not easy to tell where one color ends and another begins. There are other colors in between them.

turquoise can be seen where blue and green blend into each other. There are mixes of colors that are not next to each other.

A mixture of red and green is called brown. The red and green bands in the rainbow aren't next to each other so we don't see them mix. If the colors in the rainbow don't overlap, then they can't mix.

Black and white are not in a rainbow. When there's no light at all, black is what we see.

White is a mixture of all the colors. White light is separated from the visible spectrum when it is refracted by rain. We can't see black and white in a rainbow because we can't mix them together.

When you see a rainbow, look out for the colors you can't see.

James is an hourly paid lecturer in physics.

Under a Creative Commons license, this article is re-posted. The original article is worth a read.