Redshift Definition: Lesson for Kids

Instructor: Shoshana Yarin

Shoshana has taught all grades with an emphasis in science and has a master's degree in science.

How do scientists know so much information about outer space when we cannot travel there? One example is making calculations using something called redshift. Read this lesson to learn more.

What Is Redshift Like?

Have you ever paid attention to the sound of a passing car or motorcycle? You probably noticed that you can tell if the vehicle is coming or going by the change in sound. It's especially noticeable with a motorcycle because they tend to be louder. If the motorcycle is coming toward you, the sound is rather high pitched. Pitch is how high or low a sound is, and it's affected by the sound waves that carry the sound to you - waves closer together are higher pitched, and waves farther apart are lower pitched. After the motorcycle passes by it is then traveling away from you, and the sound will change to a low pitch. Try making the sound, 'yyyyyyyyyyooooooooowwwwwww!'

Sound Waves Moving Away from You are Farther Apart
Doppler shift

What does this have to do with redshift and outer space? Everything! Redshift is a 'shift' of light waves traveling away from Earth. It relies on the very same idea as the sound waves of a motorcycle passing by, but we describe it by how it looks (color) instead of sounds (pitch) because it has to do with light waves. Where does light come from in space? If you said the sun and the stars, you are absolutely right! Lets take a closer look at light waves.

What Is Light?

Just like sound is energy, light is energy, and light also travels in waves. Waves of different lengths (wavelength) have different characteristics, such as color. Do you know the colors of the rainbow? A rainbow represents all the different wavelengths of light that we can see, based on their wavelengths: red, orange, yellow, green, blue and purple (actually indigo and violet, but we only see a little purple). The red side is a longer wavelength and the purple side is a shorter wavelength.

Different Wavelengths of Light Make Colors

Light travels very fast, but because it has to travel so far in outer space, it takes a long time for starlight to reach the earth. How does this tie in with redshift? Read on, my friend!

What Redshift Means

As light from a star travels in waves towards Earth, the star itself is actually moving away from Earth. That means the waves of light it sends out become farther apart, or spread out, just like when the motorcycle travels away from you the waves become farther apart and make a lower pitch. That's called the Doppler shift (or Doppler effect), and it means we can gather information about a moving object because of the change in sound waves.

Redshift of a Star Moving Away

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