Have you ever looked into the sky after a rainstorm and seen a rainbow? It’s one of nature’s most beautiful sights. But, have you ever wondered how a rainbow is made and why we only see them when there is water? What gives? For help answering this colorful question, we turn to our friends at Discovery Kids.
Quick question: What color is sunlight?
That’s not a trick question, and there is an answer!
While sunlight may appear to be white to us, it is full of many different colors. Inside of each beam of light are red, orange, yellow, green, blue, indigo and violet. We don’t see these colors because the atmosphere around us, the gasses the make up the air, don’t have a refractive index (the measure of how light travels through something) that causes them to change.
However, drops of water (as well as certain pieces of glass or plastic known as prisms) cause the light entering them to behave differently. In fact, as light passes through a raindrop it slows down very slightly. What’s amazing is that all of those colors inside of light will exit at a different speed. What happens is a group of colors enters the raindrop at once, but they all exit at slightly different speeds and slightly different angles. We can't see the different in speed, but we can see the effect this has on the colors.
That is what makes a rainbow! It is sunlight entering a mist of water, either in the sky or even from a sprinkler in your yard, and having the colors separate into separate lines. Because the colors inside of light all move at different speeds and reflect at different angles, we see the same order of colors in every rainbow: red, orange, yellow, green, blue, indigo and violet.
Rainbows in the sky will only appear when there is direct sunlight shining through the water. So if it is cloudy as far as you can see, there will not be a rainbow. However, if there are clouds and water between you and the sun, you will very likely see a partial or full rainbow.
Looking for more Never Stop Asking "Why?" questions? Catch up on all of the past "Why's" on the blog!
