What is a Rainbow? | How Rainbows Form

Jul 20, 2017
Rainbows over Bryce Canyon
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What is a rainbow? Most everyone has seen a rainbow sometime in their life, but do you know how rainbows are actually formed? Here’s an explanation.

What is a Rainbow?

To put it plainly, rainbows are reflections of sunlight through raindrops. As the light is reflected, it is refracted, which means that the direction of the light wave is changed. Different wavelengths of light, which we see as colors, bend at different angles and produce a rainbow’s signature color banding, as seen in the photo below.


Light being refracted through a raindrop. Source: Wikipedia

Since sunlight is made of different wavelengths of light, we see the white light broken into an array of colors—the rainbow. The more the light bounces around, reflecting and refracting, the more types of rainbows there are.

Types of Rainbows

On December 17, 2015, rainbow scientist Jean Ricard concluded that there are 12 definitive types of rainbows.

Some of the most interesting types include the following:

  • Double rainbows: Two concentric rainbows appearing in the sky, with the higher rainbow’s colors in reverse order of the lower rainbow’s.
  • Twinned rainbows: Two rainbows appearing to stem from the same point—both presenting the typical ROYGBIV color ordering.
  • Circular rainbow: A fully circular rainbow, usually only seen from high vantage points such as skyscrapers or airplanes.
  • Monochrome rainbow: A rainbow that occurs when the sun is lower in the sky—such as at sunrise or sunset—and reflects more of one or two wavelengths than the others, making it appear monochrome.
  • Moonbow: A rainbow caused by the light of the Moon, rather than the Sun. These are typically quite dim and may even appear white in color.
  • Fogbows: A faint rainbow occurring within fog, usually over a body of water. 

The big debate is why rainbows are so different. In general, the scientists are divided between the “fatty” camp and the “low-life” camp. Most scientists have suggested that the size of the raindrops shape how they reflect light and what the rainbow will look like. Others have said that it depends where the raindrops are—since a low-lying haze of water will reflect at a different angle than a high shower of drops.


A rare winter rainbow.

What Ricard has shown with his research is that while both factors are important, what matters most is where the drops are—high or low in the sky. That’s why you see rainbows change as the raindrops fall. They can fade, brighten, split into double or multiple bows, be full circles or low arches.

If rainbows that form are too low, the thickness of the air makes it impossible to see the shorter waves of light—the purples and blues. The most low-lying droplets that are filtered through haze and smog finally filter out all but the long waves of red, producing a monochrome rainbow.


Monochrome rainbows are missing colors and may even be solid red. Source: Wikipedia

Rainbows become rare in winter, as ice scatters light instead of refracting it. So, as you sit through cold winters, dream of the all the types of rainbows that sparkle in summer skies!

Wondering where to see a rainbow? Here are the best places to look for a rainbows.

About This Blog

Are you a weather watcher? Welcome to "Weather Whispers" by James Garriss and until recently, Evelyn Browning Garriss. With expertise and humor, this column covers everything weather—from weather forecasts to WHY extreme weather happens to ways that weather affects your life from farming to your grocery bill. Enjoy weather facts, folklore, and fun!

With heavy hearts, we share the news that historical climatologist and immensely entertaining Almanac contributor Evelyn Browning Garriss passed away in late June 2017. Evelyn shared her lifetime of weather knowledge with Almanac editors and readers, explaining weather phenomena in conversation and expounding on topics in articles for the print edition of The Old Farmer’s Almanac as well as in these blog posts. We were honored to know and work with her as her time allowed, which is to say when she was not giving lectures to, writing articles for, and consulting with scientists, academia, investors, and government agencies around the world. She will be greatly missed by the Almanac staff and readers.

Reader Comments

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12 different rainbows

I was also looking for the 12 types, if you could please repost (article was fascinating) repost with pictures, ( I know of several types of bows, fire bows, storm bows, rainbows, moon bows, sun bows, bows from chemicals) thanks for your concideration.

How Rainbows Form: 12 types of rainbows

I was excited to read this article at first; but disappointed when you didn't actually let us know the 12 different types of rainbows and what causes them! :( Hearing that there were 12 different types of rainbows was actually new and interesting to me and the only reason I "clicked" to learn more; which usually Farmer's Almanac does in their links. Most everyone already knows the basics of what makes the average, ordinary rainbow listed in your post; preschool - elementary students know this. I was just hoping for a little bit more based on the title of your post.

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