How Can You Make Your Own Rainbow?

Grade range: K-3

Time to complete: 20-30 minutes

Subjects/skills addressed: Science, Math

Objective: Students will create a rainbow with sunlight and water.

Materials needed:

Garden hose with an adjustable nozzle attached

Photographs of naturally occurring rainbows

Picture of a right triangle or angle

Open space outside

Sunshine (the sun should NOT be directly above you) 

Words to know: refract, reflect, angle

Instructions:

1. Show the students images of naturally occurring rainbows (single and double rainbows).

Ask: What colors do you see in the rainbows? How do you think these rainbows are created? Look closely at the double rainbows. How are they different?

2. Show students the picture of a right triangle.

3. Demonstration:

a. Position yourself with the sun directly behind you so that you and your shadow form the legs of a right triangle, as shown.

b. Position the hose approximately halfway between your shadow and you. The actual angle is 42 degrees for the primary rainbow and 50 degrees for the secondary rainbow. However, halfway will be easier for the students to understand.

c. Have a student turn the water on FULL blast. Arc the hose spray to create the rainbow. The rainbow should be formed close to the halfway point between the legs of the triangle.

Ask: What colors do you see in the rainbow? What color is at the top? At the bottom?

4. Have the students take turns creating their own rainbow. It may be possible to create a double rainbow in this manner, but the secondary rainbow will be faint.

Conclusion: To create a rainbow you need a source of light and something that will refract and reflect the light. The light from the sun is refracted (bent) and reflected (bounced) inside the droplets of water from the hose. As each color of the rainbow has a different-sized wavelength, the way they are refracted and reflected causes the sunlight to split into the different stripes of the rainbow.

Create a rainbow in the classroom: In the story, Sometimes Snow Falls in the Summer, a rainbow is created in Ella’s room by a prism. There are many ways to create a rainbow–using CDs, water, water and oil, and many more. Try your own hand at creating rainbows in the classroom.