National Science Standards:

Content Standard A: Science As Inquiry
Content Standard D: Objects in the Sky, Changes in Earth and Sky, Properties of Earth materials

These activities demonstrate how rainbows are formed and the colors they show.

*NOTE: Activities increase in diffulculty. Educators/Parents may want to work through all activities or choose those most appropriate for their students/children.

(BACKGROUND INFORMATION)
Facts we already know about rainbows:

• You can only see rainbows if you are standing between raindrops and the Sun.
• No two people can ever see a rainbow in exactly the same way.
• There is always more than one rainbow in the sky, even though you may not be able to see more than one.
• Rainbows can be created in special ways without raindrops. This type of rainbow is called a spectrum.

Activity One - Rainbows

wide-mouthed, smooth glass container; small mirror; flashlight; dark room with light-colored walls

1. Place water into the glass container. The water should be within an inch of the opening.
2. Place the mirror into the water inside the jar. Tilt the mirror slightly upward.
3. In a dark room with light-colored walls (white is best), shine the flashlight into the water so that it shines onto the mirror. A rainbow should appear on a wall where the light bounces from the mirror onto the wall.
4. You have just created a SPECTRUM. It is like a rainbow except rainfall is not needed to create it.
5. The water in the container takes the place of the raindrops. The light is bent, so scientists call it REFRACTION, which makes light separate into its true color.
6. Draw what you see.

NOTE: If you cannot see a rainbow, change the position and angle of the flashlight.

Activity Two - Tiny Rainbows

(per student or team of students) water, eyedropper, glass slide, magnifying glass

(NOTE: This activity should be conducted outdoors in direct sunlight.)

1. Use the dropper to place a few drops of water on a glass slide.
2. Look at the drops of water through a magnifying glass.
3. You should see colors appear on the water drops. These colors create a tiny rainbow.
4. If you do NOT see colors easily, change the angle of how you look at the drops.
5. Draw what you see.

FOLLOW-UP DISCUSSION

Rainbows never form when it rains if the sky is completely covered with clouds. Rainbows form when it rains and the Sun is shining. You see a rainbow because you stand between the falling rain and the shining Sun. Rainbows in the sky are always much larger than the rainbow formed on a tiny drop of water.

Activity Three - Prisms

(per student or team of students) prism, flashlight, crayons or markers, white paper

1. A special instrument called a prism changes white light into many colors. The colors are called a spectrum. A spectrum looks exactly like a rainbow but can be formed indoors as well as outdoors without raindrops.
2. Notice that the sides of the prism are bent. The prism is different from the flat glass in a window. White light can travel straight through flat glass. Such light can never change colors.
3. Light cannot move straight through a prism. The bent sides will also make light.
4. Turn on your flashlight and turn off the lights in your room.
5. Shine the flashlight into one side of a prism. This light will travel through the prism and shine onto a wall in your room.
6. Notice the colors on the wall. If you cannot see a spectrum of colors on the wall, adjust the flashlight and observe how light shines through the prism.
7. Draw what you see.

FOLLOW UP DISCUSSION
For many years, people believed that a spectrum (also called a rainbow) has seven colors. Technically, a rainbow contains millions of colors. Our eyes only pick out colors that are easy to see. Millions of colors are made as all the colors blend together. The six main colors seen in a spectrum and a rainbow are (in order) red, orange, yellow, green, blue, and violet. Indigo used to be included as a color between blue and violet..

EXTENSION ACTIVITY

Place a colored, plastic sheet across the lens of your flashlight. Shine this colored light through the prism. Are you able to form a rainbow or spectrum? What happens?

Activity Four - CD Prisms

(per student or team of students) compact disc (CD), flashlight, white paper

1. Hold a CD in your hand. The shiny side (without the label) should face upwards.
2. Move the CD with your hand. Look closely at its surface. It should show a "rainbow" — also called a spectrum.
   NOTE: BE CAREFUL if you conduct this activity outdoors in sunlight. Make sure you do not reflect the sunlight from the CD into another person’s eyes. You can conduct this activity indoors by shining a flashlight onto the CD. You can leave the lights in the room turned on.
3. Tilt the CD so that the colored light reflects onto the white paper to help you see the colors more clearly.
4. Draw what you see.

FOLLOW UP DISCUSSION
Light is made of waves and travels as waves. Like waves in an ocean, one wave can touch and interfere with another wave as it moves. On a CD, light waves reflect off the microscopic ridges and overlap and interfere with other light waves. This effect is actually called interference. Sometimes, waves can combine, which makes certain colors look very bright. Other waves can cancel each other, which means certain colors will disappear.
Some stores carry what are commonly called "rainbow glasses," which will cause light going through the material to bend before it reaches your eyes. This bending of the light makes your eye see colors.

EXTENSION ACTIVITY

Place a colored, plastic sheet across the lens of your flashlight. Shine this colored light at the compact disc. Are you able to form a spectrum? What happens?