Dictionary Definition

An arc of all seven spectrum colors appearing in the sky opposite the sun as a result of the refractive dispersion of sunlight in drops of rain or mist.

Formation

Explanation

Raindrops are formed when the sun is far down in the sky and it shines on a shower of rain or spray. The sunlight passes through the drops of water and bends as it passes to the far side, separating the seven colors that make up white sunlight. Each color is slightly different in length, so it reaches your eyes from a different direction to form bands. Read about Light Spectrums below to learn more about how color works.

Experiment #1: Making a Rainbow

What You'll Need:

• garden hose
• sunshine

Directions:

1. Turn on the hose in your backyard.
2. Turn your back to the sun.
3. Shoot the water from the hose upward into the sky.
4. Watch what happens in the sky.

What's Happening?

When you spray the hose into the sky, the sun will create a rainbow. It is just like its raining because you are making it rain with the hose, so the same process happens and the rainbow is formed. The sunlight is hitting the drops of water at a slant, and the colors separate to be reflected into a rainbow. Read the explanation above to learn more about what forms rainbows.

Experiment #2: Making Another Rainbow

What You'll Need:

• mirror
• pan with water
• white wall
• sunshine

Directions:

1. Fill the pan with water and set it outside next to a white wall.
2. Set the mirror at a slant in the pan and hold it so the sunlight hits it.
3. Look at the wall to see what forms.
4. Stir the water and see what happens.

What's Happening?

When you reflect the sunlight through the mirror, the colors separate and form a rainbow on the wall. However, when you stir the water the colors come together again and the rainbow is gone. Learn more about how a rainbow forms by reading the explanation above.

Types

The rainbows you see in the sky come in different types. Read below to learn more about different kinds of rainbows.

• Primary Rainbow: This type appears when droplets reflect light only once. It has bands of color ranging from red to violet with red on the top.
• Secondary Rainbow: This type comes from droplets that reflect light twice. It has bands of color also ranging from red to violet, but with violet on top.
• Extra Reflections: When the droplets reflect sunlight even more times, more rainbows are formed. However, the more times the raindrop reflects light, the weaker the rainbows are.

Light Spectrum

Explanation

Light travels in waves of different sizes. Some are short, some are long, and some are in between. When we see colors, we are seeing light at different wavelengths.

Sunlight, called white light, appears colorless but is really a mixture of many colors. When a rainbow appears in the sky after rain, you can see some of the colors of the sun's rays. As sunlight is reflected through the raindrops it is refracted (bent). Light with long wavelengths, such as red, is bent more than light with short wavelengths, such as violet. So, the colors fan out as they come together again.

About 300 years ago, the English physicist Isaac Newton made a discovery. When he shined a beam of sunlight through a slit in a dark room onto a prism, the prism refracted the white light into a spectrum of colors. With another prism in the spectrum, they combined again to form white. This proved that white light is made up of different colors.

A spectrum is a range of colors, from those with long wavelengths to those with short wavelengths and all the others in between. You can make your own spectrum by doing the experiment below.

Experiment #3: Creating a Spectrum

What You'll Need:

• glass with straight sides
• piece of card with 1/2 inch (1 cm) slit
• sheet of white paper
• adhesive tape

Directions:

1. Fill the glass with water.
2. Tape the glass to the card so the center of the glass is on the slit (see picture at right).
3. Place the white paper close to a window and stand the glass on it.
4. Watch what happens when the sun passes through the slit behind the glass.

What's Happening?

When the sun passes through the slit of the card, it is refracted by the water in the glass. This makes a spectrum on the paper below. Read the explanation above to learn more about the color of light.