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The Science Behind Fully Double Rainbows

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Throughout history, mankind has interpreted the appearance of a rainbow in the sky as a good omen –– a sign that the storms have passed and better days are ahead; a bridge between the earthly realm and that of the heavens; or even a marker pointing to the location of a hidden pot of gold!

However you interpret the appearance of a rainbow, we now know that there is a scientific explanation for why it occurs in the first place. But if you’re especially lucky, you may have seen a fully double rainbow, where you get two rainbows for the price of one! Let’s take a look at the science behind these incredible optical phenomena!

What Causes Any Rainbow?

Before we explain the science of double rainbows, let’s review the science behind a single rainbow. A single rainbow is an optical illusion created by the reflection, refraction, and dispersion of light through the prism of a water drop.

When sunlight emerges through the clouds following a rainstorm, that light hits the water drops that are still floating or falling through the sky. Some of the sunlight is reflected right away, but some of it enters the water drop and as it does, it is refracted at the surface. When this light hits the back of the raindrop, it bounces back and once again leaves the raindrop. Only now, the light has been separated into its individual color frequencies. The result is a rainbow of color that exits the raindrop.

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The colors of the rainbow are the same for everyone: red, orange, yellow, green, blue, indigo, and violet (ROYGBIV). In a single rainbow, red is the most prominent color and appears as the ‘top’ band of color. This is due to the properties of light, including frequency and wavelength, of which you can learn more here.

Last but not least, a rainbow does not have a physical presence; it is an optical illusion and its ‘existence’ depends on the position of the observer’s head. So while the good news is that science, light, and color are endlessly fascinating, the bad news is that you’ll never be able to follow a rainbow to its end to find a pot of gold!

What is a Double Rainbow?

During a fully double rainbow, you will notice that one rainbow is noticeably brighter than the other. This brighter rainbow is called the primary rainbow. The primary rainbow, as we described above, is the result of light reflecting off of water drops once, then reflecting back out of the drop.

The second rainbow is called, you guessed it, the secondary rainbow. Secondary rainbows appear due to a phenomenon that is similar to the primary rainbow, with one big difference: the light that enters the raindrop and refracts at the surface does not escape after hitting the back of the raindrop. Instead, that light is refracted a second time, creating the secondary rainbow

The Differences Between Primary & Secondary Rainbows

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There are a few key differences between primary and secondary rainbows. First, the colors of the secondary rainbow are inverted from the primary rainbow. That’s right: the colors of secondary rainbows are the opposite of primary rainbows, moving from violet, indigo, blue, green, yellow, orange, and red (VIBGYOR).

You’ll also notice that this rainbow is not as bright; secondary rainbows are always fainter and harder to see than primary rainbows. This is because the amount of light that is refracted a second time (rather than escaping the raindrop) is much less than the amount of light responsible for creating a primary rainbow. Finally, the shape and location of the secondary rainbow are going to be about 10 degrees outside of the primary rainbow and it will radiate at an angle of 50 degrees.

A secondary rainbow is an exceptionally rare sight, so if you do happen to spot a double rainbow stretching all the way across the sky, consider yourself lucky!

Meanings for Double Rainbows

While we always want to make sure we understand the science behind rainbows, it’s always fun to explore the spiritual and philosophical meanings associated with them, too. For example, in some Eastern cultures, the dual arc of the fully double rainbow represents transformation. The primary rainbow symbolizes the physical world, while the secondary rainbow represents the harder-to-see spiritual world.

What does a double rainbow mean to you?

Double Your Fun!

The only thing more fun than studying the science of rainbows… is studying the science of fully double rainbows! At Rainbow Symphony, we want to give you the tools you need to advance your education and make it fun to study rainbows, refraction, reflection, and diffraction. That’s why we have a wide variety of plastic diffraction glasses and rainbow glasses –– available multiple colors and styles. It’s an affordable way to continue learning for yourself or help your class understand the science behind this mysterious phenomenon.

We offer worldwide shipping, 30-day returns for an exchange or a refund, and 10% off your first order when you sign up for a refund! We also offer bulk order pricing and custom printing on our paper glasses. If you have any questions about our products or want to inquire about customizing your glasses, don’t hesitate to give us a call at 818-708-8400, or by emailing us at rainbowsymphony@rainbowsymphony.com

Science Of Double Rainbows