# What’s in a rainbow?

#### OpticsReflection & RefractionElectromagnetic SpectrumVisible LightWeather & ClimatePerception

Rainbows are the best part of a rain shower. In my opinion, 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 mention 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! Rainbows are, in fact, beautiful optical illusions. 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. Each of these colours have a different wavelength. Light travels in waves, and each wave has a different length between its peaks (or its crests, as scientists call them). In the diagram below, you can see that red has a longer wavelength than violet.

##### Above: Red has a longer wavelength than violet. Image © Let's Talk Science, 2018

When light enters a water drop, the different colours 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, pencils in water look broken, like in the diagram below.

##### Above: Image © Theresa_knott, Wikimedia Commons

Did you know? You can see rainbows at night! They're called moonbows. Their colours are reflected by the reflection of the moon. They're aren't as bright as normal rainbows, and they're much more rare.

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

##### Above: Image © Theresa_knott, Wikimedia Commons

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.

The rainbow’s interior colours are always slightly brighter than the exterior colours. This is due to the angle at which we see the rainbow. The inside of the rainbow is where the majority of light reflects into our vision, making the colour brighter. Meanwhile, there’s less and less light reflected at the outer limits 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, you would be looking at the rainbow in front of you.

The rainbow is constantly moving. So if you do go on a leprachaun hunt, you’ll be looking for quite some time!

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

Hip Hop Jewellery (2017)
Let’s Talk Science

How Rainbows Work (2002)
How Stuff Works

Refraction of Light in Water (2017)

The Science of Rainbows (2016)
Smithsonian Science Education Centre

### References

Rainbow (2018)
National Geographic

Reflection Optics (2003)
Atmospheric Optics

Light Inside the Rainbow (2000)
Patterns in Nature

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