What's in a Rainbow?

In my opinion, rainbows are the best part of a rain shower. For me, they make the rain worthwhile. I’m not the only one who thinks so. Rainbows appeared in ancient Greek, Chinese, Indian and Norse mythology thousands of years ago.

Did you know? 

One of the oldest mentions of rainbows happens in the Epic of Gilgamesh, an ancient text dating from about 2150-2000 BC.

According to Irish tradition, leprechauns hide their gold at the end of the rainbow. So how can we reach the end of the rainbow? We can’t, because there isn’t an end! Every rainbow is actually a full circle of reflection.

Surprising, right? But when we’re standing on the ground, looking up to see the colorful arch, we are only seeing half the rainbow. You could see the full circle if you were in a plane or climbing a high mountain. That’s because you would be above the ground and could fully see the reflection and refraction of light traveling through the water in our atmosphere. Let’s examine these two processes.

How does a rainbow happen?

When water and light meet, the white light travels through the water and separates into its colours. Light is made of seven basic colours: red, orange, yellow, green, blue, indigo and violet. Light travels in waves, and each wave has a different length between its peaks (or its crests, as scientists call them). This is called its wavelength. Each of the colours in a rainbow has a different wavelength. In the diagram below, you can see that red has a longer wavelength than violet.

 When light enters a drop of water, the different colours of light bend at different angles, causing them to separate. This process is called refraction. You can see refraction at home by placing a pencil in water. Light travels through water and air at different speeds and directions. Because air and water are different mediums, drinking straws in water look bent. The diagram below shows this same concept with a pen and pencil. 

Did you know? 

You can see rainbows at night! They're called moonbows. Their light source is the reflection of the Moon. They're aren't as bright as normal rainbows, and they're much more rare. 

The different colours of light also bounce off the inside of the water drop. This is reflection. Each raindrop reflects light similar to a disco ball! 

Did you know?

When you see more than one rainbow in the sky, they’re likely reflection rainbows. These happen when the original rainbow is reflecting in calm water, and sunbeams at different angles cause another rainbow to form. 

Have you ever noticed that a rainbow’s interior colours seem slightly brighter than the exterior colours? This is due to the angle at which we see a rainbow. The interior part of the rainbow is where the majority of light reflects into our eye, making the colour appear brighter. Meanwhile, there’s less and less light reflected at the outer part of the rainbow.

Where is the rainbow?

So you now know quite a bit about rainbows. But don’t start looking for leprechauns and their pots of gold just yet! Rainbows do not exist at a specific location. The position of the rainbow depends on the position of the viewer and the position of the Sun.

Interestingly, the position of a rainbow in the sky is always in the opposite direction of the Sun. For example, if the Sun were shining on your back, the rainbow would be in front of you.

Rainbows are an amazing feat of optics and nature. Their beauty is worth more than gold! 

Did you know? 

The physicist Ibn al-Haytham (965-1039) was one of the first scientists to attempt a scientific explanation for rainbows.