What’s the Science Behind Rainbows?

Rainbows might seem like magic, but there’s real science behind those beautiful bands of color. Whether you’re a curious student or a classroom teacher, this guide explains how rainbows form, why they appear after rain, and even how to make your own rainbow at home.

How Are Rainbows Formed?

Rainbows happen when sunlight interacts with water droplets in the air. Here’s the process, step by step:

• Refraction: Sunlight bends as it enters a water droplet.

• Reflection: It bounces off the inside of the droplet.

• Refraction again: The light bends once more as it exits.

  
  

This bending and bouncing separates the sunlight into its different colors—creating the rainbow we see.

“Sunlight enters a raindrop, bends, bounces, and exits as a rainbow of colors.”

Are Rainbows Caused by Reflection or Refraction?

Both! Reflection and refraction work together to make rainbows:

• Refraction bends the light as it enters and exits the droplet.

• Reflection makes the light bounce inside the droplet.

This process splits white sunlight into a full spectrum of colors.

Why Do Rainbows Appear After Rain?

Rainbows need two key ingredients: sunlight and water droplets.

After a rainstorm, the air is filled with tiny droplets. If the sun comes out and you stand with your back to it, the sunlight can pass through those droplets and form a rainbow.

“Rainbows appear when sunlight meets raindrops at just the right angle.”

That’s why you don’t see rainbows every time it rains—everything has to line up perfectly.

Why Are Rainbows Curved?

Rainbows always form part of a circle because of how light travels through millions of raindrops at the same angle. That’s why you see a curved arc.

Fun fact: If you’re ever in an airplane with the sun behind you, you might see a full-circle rainbow!

What Are the Colors of the Rainbow?

Rainbows always appear in the same color order:

Red, Orange, Yellow, Green, Blue, Indigo, Violet

An easy way to remember them? Just say ROYGBIV—each letter stands for one color.

Can You Make a Rainbow at Home?

Yes! Try this easy science activity:

What you need:

• A clear glass of water

• A sunny window

• A white sheet of paper

Steps:

1. Place the glass on a sunny windowsill.

2. Hold the paper beneath the glass.

3. Tilt the glass until a rainbow appears on the paper.

You can also create a rainbow with a garden hose:

• Stand with your back to the sun.

• Spray a fine mist into the air.

• Look for a rainbow in the mist!

What Is a Double Rainbow?

A double rainbow happens when light reflects twice inside a droplet before exiting. The second rainbow appears fainter—and its colors are reversed!

Rainbow Science Vocabulary

• Refraction: Bending of light as it passes through a material (like water).

• Reflection: Bouncing of light off a surface.

• Spectrum: The full range of colors in light.

• Droplet: A very small drop of water.

Rainbow Fun Facts

• Rainbows are full circles

  We usually see only a semi-circle from the ground, but from a plane or mountaintop, you might spot a full circle rainbow!

• You can’t reach the end of a rainbow

  Rainbows aren’t physical objects—they’re optical illusions that move with you. T

• You need sunlight and water

  Rainbows appear when the sun is low in the sky and water droplets fill the air—usually after a rainstorm or near waterfalls.

• Each raindrop makes its own rainbow

  What we see as a single rainbow is really the combined effect of millions of tiny rainbows from different droplets.

• No two people see the same rainbow

  Because your viewing angle is unique, the rainbow you see is slightly different from the one someone next to you sees.

• Rainbows can happen at night

  These are called “moonbows” and they’re created by moonlight instead of sunlight—though they’re usually much fainter.

• Rainbows always appear opposite the sun

  If the sun is in the west, the rainbow will form in the east. That’s why you need the sun behind you to see a rainbow.

Try This in the Classroom

Rainbow Garden Hose Activity

• Go outside on a sunny day.

• Spray a mist of water with a hose.

• Look for the rainbow arc where the mist and sunlight meet.

Or use a prism to split sunlight into a rainbow on your classroom wall!

Rainbows help us explore important science concepts like light, weather, and color. They’re also a great way to spark curiosity—and bring a little wonder into any classroom.