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15 minutes
What do I need?

  • a hose that can spray, a sprinkler, or a fountain
  • a warm, sunny day
 Rainbow girl

What do I do?
1Stand near the spray of water drops. Stand with your back to the sun. Find your shadow. It should be between you and the spray. If it isn't, move around until it is.

   3If you don't see a rainbow, here's how to find one. Look for the shadow of your head. Hold both arms straight out in front of you. Spread your hands as wide as they will stretch with your thumbs touching, tip to tip. Place the tip of one little finger so that its shadow falls in the center of the shadow of your head.

Wow! I didn't know that!
When you look at a rainbow, you see seven colors. They are always in the same order--red, orange, yellow, green blue, indigo, and violet. An easy way to remember the colors and the order is to think of the name ROY G. BIV, spelled from the first letter of each color.

4When you move, the rainbow moves with you. Someone standing next to you may also see a rainbow in the spray, but their rainbow will be in a slightly different place. Each person sees his or her own personal rainbow.

Family points out rainbows

 


2Look for a rainbow in the spray.

 

...hold arms straight out...

 

Keeping that finger in place, look at the sunlit drops that line up with your other little finger. You should see rainbow right there.

...look between your hands...

 

 

 If you do this with your family, ask everyone to point to the top of the rainbow they see. Each of you will be pointing to a different spot.  

What's going on?

Why does sunlight shining through water drops make a rainbow?
Whenever light moves from air into something clear (like water or glass), it slows down just a little bit. If it hits the water or glass at an angle, it bends as it slows down. This bending is called refraction.

Just how much light bends when it hits water or glass depends partly on the color of the light. The white light of the sun is made up of all the colors of the rainbow. When this sunlight reflects off water drops (or shines through a prism), each of these colors bends at a slightly different angle, fanning out to make a rainbow.

Bending rays of light form a rainbowWhy do I have to stand with my back to the sun to see a rainbow?
To make a rainbow, sunlight has to shine into a raindrop (bending as it moves from the air into the water), bounce off the far side of the drop , and then leave the drop (bending again as it moves from the water to the air). So if you're going to see a rainbow, you have to be standing where your eyes can intercept this colored light. That means you have to stand with your back to the sun, so that the sunlight is shining into the raindrops from over you shoulder.

Knowing this helps you know when to look for rainbows in the sky. You're likely to see a rainbow when the sun is low in the western sky and sunlight is shining on raindrops to the east. At the same time of day, you won't see a rainbow in raindrops that are west of you. That's because you're facing into the sun.

What else can I see when I'm looking for rainbows?
If condition s are right, you may see two rainbows--one inside the other. The inner, brighter arc is the primary rainbow; the dimmer, outer arc is the secondary rainbow. Notice the order of the colors in your rainbow. In the primary rainbow, red is on the outside of the arc and violet is on the inside. In the secondary rainbow, the colors are in the same sequence, but violet is on the outside and red is on the inside.


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This and dozens of other cool activities are included in the Exploratorium's Science Explorer books, available for purchase from our online store.

About the Books

Published by Owl Books,
Henry Holt & Company, New York,
1996 & 1997

ISBN 0-B050-4536 & ISBN 0-8050-4537-6,
$12.95 each






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