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Colorful Connections: The Science Behind Rainbows

Rainbows give excitement, awe and inspiration to most everyone who views them. They are beautiful, magical and fleeting. Read on to discover the science behind rainbows.

Photo via Shutterstock

Rainbow Requirements

A rainbow has three requirements:

1. Sunlight

2. Water droplets

3. The correct angle between the sunlight, the water droplets and the observer’s eyes.

How It Happens

To understand how a rainbow works, you need to understand three scientific actions.

Photo by Angela Rafac

1. Refraction: Put a pencil in a glass filled with water. What do you see? Refraction is the bending of light when it passes from one substance to another. The two substances the pencil is in are air and water.

2. Reflection: Go look in a mirror and smile. That is your reflection. Reflection is the return of light, heat, sound or energy after it hits a surface.

3. Dispersion: Grab a deck of cards and throw it up in the air. You have taken a compact deck of cards and dispersed it to individual cards that are spread all over the floor. Now pick it up! Dispersion is the breaking up or scattering of something.

Photo by Angela Rafac

We see a rainbow when moving light hits a water droplet and (step 1 in the illustration above) refracts (bends), then it continues on to the back of the drop and (2) reflects. It heads back toward the front of the drop and (3) refracts (bends) again. Sunlight is white light. When it refracts, the light is (4) dispersed into all the colors of the rainbow. Ta-da!


Photo by Angela Rafac

White light is made of all the colors of the rainbow. Each color travels at a different wavelength, which means each color bends at a different angle. Red bends the least, violet bends the most and the other colors fall in between.


Every rainbow you see is your rainbow! Because the angle between the sunlight, the water droplets and your eyes is an ingredient to viewing a rainbow, every rainbow is unique to the viewer, even if another person is standing right next to you.


A rainbow can be a full circle! If we are standing on the ground, the horizon will prevent us seeing from a circular rainbow. But from an airplane, you just might be lucky enough to see a full-circle rainbow!

Make a Rainbow

You can make a rainbow a number of ways.

Grab a CD or DVD and place your finger in the hole with the shiny side facing up. Tip, tilt and move around to catch the sunlight or even a light inside. You can see the rainbow on the shiny disc. Look around at the walls and ceilings to see the rainbow being projected.

Head outside on a sunny day and turn on the garden hose. Place your thumb over the opening, or if you have a nozzle turn it to spray. Can you see a rainbow? Change the direction or strength of the spray. Can you change your rainbow?

“The Rainbow Thrower”

The rainbow thrower

Squints his eye

And hurls his color

‘Cross the sky.

While far beyond

Horizons gate

The rainbow catcher

Sits and waits.

-Shel Silverstein, “Every Thing On it”


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