## NASA's Space Place Archives

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## NASA's Space Place

### What Can We Learn From Light?

By Teagan Wall

When you look up at the night sky and see stars, what you’re seeing is light produced by those stars many years ago. Because this is how we study the stars, it helps to know a few cool things about light.

For example, light always travels at a constant speed, called the speed of light. It doesn’t matter if the star giving off light is moving towards us, or away from us. This is different than most things.

Think of riding a skateboard while throwing a baseball. If the skateboard is moving toward the target when you throw the ball, the speed of the skateboard and the speed of the thrown ball combine. This means that the ball travels faster than it would have if you just threw the ball while standing still. But, if the skateboard is traveling away from the target when you throw the ball, the ball travels slower than it would have if you threw it while standing still. With light, though, it doesn’t matter how fast the skateboard is moving, the light will always travel at the same speed.

Another fun fact about light is that it is made out of waves—kind of like the waves in the ocean—and those waves can come in different frequencies. The frequency measures how many peaks of a wave pass a certain point within a set amount of time. To understand how this works, think of a beach. If only one wave washes up on shore every minute, that’s pretty slow, or a low frequency. If one wave washes up every second, that’s more frequent. We’d say that those waves have a higher frequency.

With light, the frequency determines the color or type of light. We can see the colors of the rainbow: red through violet. Red is low frequency light and violet is higher frequency. There are also types of light that we can’t see that have a higher or lower frequency than the waves of visual light. We can use special telescopes to “see” these types of light coming from space too!

And these telescopes help NASA scientists to understand the stars and universe!