What is a Rainbow? How Do Rainbows Form?

What is a Rainbow?

It takes both the sun and rain to make a rainbow! To put it plainly, rainbows are produced by sunlight entering water droplets, bouncing around each individual bead of water, and changing direction (refracting) to reflect off the back of the droplet to return back toward us.

In raindrops, sunlight bounces back, or reflects, most strongly at a certain angle of 42 degrees. If you draw an imaginary line from your eyes to the rainbow, and then back to the sun, that angle will always be 42 degrees. However, the sun has to be behind you, not in front of you, because the light gets refracted back in the general direction it came from!

The Colors of a Rainbow

Since sunlight is made of different wavelengths of light, we see the white light broken into an array of colors—the rainbow.

The colors of the rainbow in order, are red, orange, yellow, green, blue, indigo, and violet. You can remember them with the acronym Roy G Biv!

As you can see in the image above, the red light is the strongest color, and exiting  the water drop at an angle of 42 degrees relative to the incoming sunlight. The violet light emerges at an angle of 40 degrees. Other colors of the rainbow leave a raindrop at angles somewhere in between. 

Types of Rainbows

The more the light bounces around, reflecting and refracting, the more types of rainbows there are.

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:

1. Double rainbows: This happens when the light is reflected twice in the raindrop. The higher rainbow is fainter and the colors will be reversed!
2. Circular rainbow: You can see the rainbow as a complete circle if you’re in an airplane or high in a skyscraper. It’s only on the ground that you can only see the semi-circle “bow.”
3. Twinned rainbows: Two rainbows appear to stem from the same point—both presenting the typical ROYGBIV color ordering.
4. 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.
5. 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. Learn more about Moonbows.
6. 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.

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.

Rainbows become rare in winter because water turns to ice or snow! Ice scatters light instead of refracting it. 

Can You Ever Get to the End of a Rainbow?

So, let’s get to the real question.  Nope, you can’t! A rainbow is based on the orientation of the observer (you) and the light source (the sun). So, when you move, the rainbow will move, too. 

However, don’t be discouraged. Here’s the magic: Every rainbow is unique to only you!!  That’s right. Even if someone is standing nearby, you’re not seeing the same rainbow. A rainbow isn’t something you can touch! It’s an optical illusion! Every rainbow looks different and is in the eye of the beholder. We’re sure there’s a message here somewhere!

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