# What's in a Rainbow?

Rainbows are beautiful examples of optics in nature. We see them thanks to the reflection and refraction of visible light and water.

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.

• Have you ever seen a rainbow? When and where did you see it?
• Why do you think there is so much folklore and mythology about rainbows?
• Have you ever observed rings of light around the Sun or Moon? What sort of weather was happening at the time?
• Many things are soluble in water. Can a rainbow occur in instances other than when it’s raining? What practical things might a rainbow indicate?
• Rainbows are common in the myths of different cultures. What cultures have rainbows in their myths? What things do rainbows represent in various myths?  (Note: This question may require additional research.)
• Investigate the different types of rainbows that can occur.
• What is a Sundog and a sun halo? What is a moon halo? How are these the same or different from rainbows? (Hint: You may have to do some research to find the answer.)
• How are double rainbows formed?
• Use a prism to create a spectrum of visible light. What does the prism do to the beam of white light? How does the shape of the prism affect the resulting spectrum? What is the property of light that causes the light to separate?
• Investigate some of the early scientific research on rainbows. What were some of the early scientific ideas about how rainbows were formed?
• What do scientists investigate about rainbows? How might this research be useful?
• Do scientists have to wait for it to rain before they can study rainbows? Do scientist simulate rainbows? How is this done?

(Note: You may have to do some additional research to answer these questions.)

• Can you think of any movies or popular songs about rainbows? If you cannot think of any, do some online research.
• What do rainbows tend to represent in imagery or as symbols?
• This article and the connecting resources support teaching and learning in Physics and Math and can be used to introduce concepts connected with the topic of light, the visible spectrum and optical phenomena. Key concepts introduced in the article include rainbow, reflection, refraction and wavelength.
• Begin the lesson with an Admit Slip to activate students’ prior knowledge about rainbows. Download ready-to-use reproducibles using the Admit Slip learning strategy for this article in [Google doc] and [PDF] formats.
• Have the student read the article and view the video The Science of Rainbows
• After reading the article and viewing the video, the teacher could have students complete a Print-Video Venn Diagram learning strategy to organize and compare the information provided in both resources. Download ready-to-use Print-Video Venn Diagram reproducibles in [Google doc] and [PDF] formats.

How to Prisms Work (2017)

This article for Sciencing, by John Papiewski, explains how light refracts through a prism to create a rainbow of light.

How do rainbows form? (2014)

A Met Office - Weather video (1:23 min.) explains the conditions that must occur for a rainbow to be visible in the sky.

## References

Harris, T. (2002, May 28). How rainbows work. How Stuff Works.

Henderson, T. (n.d.). Reflection, refraction, and diffraction. The Physics Classroom.

Treviño, J. (2019, January 8). How is a rainbow formed? Popular Science.