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Unveiling the Secrets of How Rainbows Form and Dazzle Our Senses

Rainbows are one of nature's most stunning spectacles. But how are they formed? Learn about the science behind them.

By Gemma Tarlach
Apr 22, 2019 5:00 AMMar 28, 2024 3:57 PM
Rainbow Refraction Prism - Shutterstock
Refraction splits white light into a spectrum of colors. (Credit: Petrroundy43/Shutterstock)


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Why are there so many songs about rainbows? It could be because the meteorological phenomena, beautiful yet ephemeral, inspire our inner romantics.

Or maybe it’s because of the mesmerizing optical properties of their vibrant hues. Either way, explanations behind the formation of rainbows have enchanted cultures for centuries.

Unique Facts About Rainbows

While most people are familiar with the basic concept of rainbows, there are numerous intriguing aspects and lesser-known facts surrounding these magical arcs of light. Here are five fascinating things you probably didn't know about rainbows.

1. How are rainbows formed?

Rainbows occur when sunlight — including all wavelengths of visible light, which together appear as white light — pinballs in and out of water droplets (usually rain, but sometimes water spray, or the droplets that form mist or fog).

Refraction splits white light into a spectrum of colors. (Credit: Petrroundy43/Shutterstock)

Some of the light is reflected off the drop’s outer surface, but the rest of it enters the droplet, skidding as it does so. This skid, or refraction, occurs because water is denser than air. As the light enters the droplet, it slows and changes direction.

Think of what would happen if you were speeding along the freeway, and the asphalt suddenly turned to mud. Once inside the droplet, the light reflects off the back inner surface, then refracts a second time, bending as it travels out of the water and back into the air.

Because the droplet is spherical and its surfaces are not parallel, all this skidding in and out happens at slightly different angles for the different wavelengths of visible light, so the exiting white light disperses into a spectrum of colors.

2. How many colors are in a rainbow?

The number of colors an individual perceives in a rainbow depends on expectations, which are the product of culture. Ancient philosophers and physicists reveal different perspectives on the colors in a rainbow.

(Credit: Peter Maerky/Shutterstock)

Aristotle, for example, wrote of only three colors in the rainbow: red, green and violet. Some early Islamic scholars also saw a tricolored rainbow, but it was red, green and yellow. Medieval proto-scientist Roger Bacon described five colors; so did early Chinese scientists and philosophers.

Only after Sir Isaac Newton, in the 17th century, linked perceived colors in a rainbow to notes on a Western musical scale did European scientists agree that there were seven colors.

Read More: The Meaning of Colors

3. Where is a rainbow in relation to the sun?

A rainbow will always be opposite the sun. Imagine a line from the sun, which will be somewhere behind you, through the back of your head and out your eyes, ending at the shadow of your head on the ground. Any rainbow you see will be centered around that axis. Someone standing beside you may also see a rainbow, but it will be around an axis running from the sun to their head shadow.

Phenomena such as parhelia and halos are beautiful, but they're not rainbows. (Credit: Mangus Edbäck)

If you think you’ve spotted one near or around our day star, you’re seeing something else. A parhelion, also known as sundogs, may appear as rounded or spiky arcs on either side of the sun. Halos, meanwhile, circle the sun. Both phenomena result from hexagonal ice crystals in high-altitude clouds acting as prisms.

4. What is a fire rainbow?

Fire rainbows have nothing to do with rainbows, either. (Or with fire, for that matter.) More accurately known as circumhorizontal arcs, fire rainbows appear horizontally and are another product of high-altitude ice crystals refracting light.


Fire rainbows are not as well-known or frequently seen as traditional rainbows. They should also not be confused with the flaming rainbow bridge of Norse mythology.

Read More: Does Fire Have a Shadow?

5. What is a rainbow bridge?

The Bifröst myth is likely the inspiration for a certain modern folk tale: When beloved pets die, the story goes, they cross the Rainbow Bridge to an idyllic place where they await their owners.

In Norse mythology, Bifröst was a rainbow bridge to the gods. (Credit: Emil Doepler, 1905)

Pet lovers and Vikings aren’t the only ones to see rainbows as a connection between the worlds of the living and the dead. That rainbow, called Bifröst, joined the mortal world with that of the gods. Upon death, worthy souls would cross it into Valhalla.

In fact, the legend of Bifröst may be rooted in the rainbow pathway traveled by Greek and Roman messenger goddess Iris. Other, even older Asian and Native American traditions also see the colorful arc as linking our world with another.

People today are still awestruck by the remarkable qualities and symbolism of their exquisite appearance. Science may tell us that rainbows are roads to nowhere, but worldwide their allure endures — for the lovers, the dreamers and me.

Read More: Optical Illusions Are Weirder Than You Think

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