What is a traveling wave?

A traveling wave is a shape that carries energy from one place to another, like a wiggle moving down a jump rope.

What do scientists call the tiny rings that move across water when you tap it?

Scientists call the tiny ripples on top of the water surface tension waves.

How is red light different from blue light?

Red light is a very long wave that takes big steps, while blue light is a short wave that takes tiny steps.

If you take tiny, fast steps in a walking game, what kind of wave does that show?

Taking tiny, fast steps leaves a small space between footprints, which shows a short wavelength.

What happens to short blue waves when they hit tiny bits in the air?

Short blue waves crash into the tiny bits in the air and bounce all over the place, which makes the sky look blue.

Light Travels in Waves

Why the Sky Changes Colors — illustrated by glass prism refracting sunlight into a gradient spectrum, Victorian botanical illustration style. — **Why the Sky Changes Colors**

Have you ever watched the ocean? Water rolls toward the beach. That rolling motion is a wave.

Light moves just like those water waves! A wave is a moving shape. It carries energy from place to place .

You and a friend hold a jump rope. You shake your end up and down. A wiggle travels down the rope.

That wiggle is a traveling wave . Light travels from the sun to your eyes. It travels in that exact same way.

Light does not need a rope. It does not need water. Light can travel through empty space.

It moves very fast. It zooms all the way to Earth.

Think about a stadium full of sports fans. Sometimes the fans do a giant wave. One person stands up and sits down.

Then the next person stands up. The people do not walk around the stadium. Only the shape of the wave moves.

Light waves work the exact same way. The wave shape travels forward.

Making Waves You Can See

We can not easily see light waves. They move much too fast. They are also much too small.

But we can look at water. Water helps us understand them. Scientists often use water to show wave rules .

Try this fun trick at home. Fill a baking pan with water. Let the water get perfectly still.

Then, tap the water lightly with your finger. You will see tiny rings. The rings move outward from your finger.

Scientists call these surface tension waves . Light moves through space in a similar pattern. It ripples outward from the sun.

It travels in straight lines. It ripples just like those water rings.

Measuring the Waves

Not all waves look the exact same. Some waves are very wide. Other waves are very narrow.

We measure them by their wavelength. Wavelength is a special distance. It is the space between two wave tops.

You can measure it with a ruler. Let us use a walking game. This game helps us understand wave sizes.

You take giant, long steps. You leave a big space between your footprints. That is a long wavelength.

Next, you take tiny, fast steps. You leave a small space between your footprints. That is a short wavelength.

Light waves have different step sizes too.

Let us look at a slinky toy. You can stretch a slinky on the floor. You can wiggle one end side to side.

You will see big curves move. Those big curves have a long wavelength.

Now wiggle the slinky very fast. You will see lots of small, tight curves. Those tight curves have a short wavelength.

Light waves can be stretched out. Light waves can also be squished together.

Colors Are Different Sizes

In our last lesson, we learned rainbow colors. Those colors are actually light waves! Each color has its own special wavelength.

Teachers draw waves in different ways. They want to help students learn . Some teachers draw wavy lines.

Other teachers draw arrows . Both pictures show the exact same thing. They show different color sizes.

Here is the big secret about light. Red light is a very long wave. It takes big, lazy steps.

Blue light is a very short wave. It takes tiny, fast steps. Yellow light is right in the middle.

It has a medium wavelength. It takes normal steps. Every single color has its own exact size.

Color	Wave Size	Step Size
Red	Long	Giant
Green	Medium	Normal
Blue	Short	Tiny

All these colors travel together. They come from the sun at the same time. They mix together to make white light.

Why Wave Size Matters

The size of the wave is very important. It changes the behavior of the light. Big waves act differently than small waves.

Soon, we will learn about the Earth's air. We will also learn about tiny air bits. Sunlight hits those tiny bits.

The waves crash into them. The big red waves step right over them. They keep going straight.

The short blue waves crash into the bits. They bounce all over the place! This bouncing is very important.

This bouncing makes the sky look blue. We will learn more about that bouncing soon!

Key Terms

Wave — A moving shape that carries energy from one place to another.
Traveling Wave — A wave that moves forward through space or down a line.
Wavelength — The distance from the top of one wave to the top of the next wave.
Surface Tension Wave — Tiny ripples that move across the top of still water.