When astronomers analyze the light that comes from distant stars and galaxies, they can tell a lot about their motion because of the Doppler effect. Every element within a star has a specific pattern of light frequencies that it emits as the star shines. When looking at distant galaxies, astronomers observe the expected pattern for an element, but every frequency slightly shifts toward the red side of the spectrum. The light is experiencing a Doppler shift because the galaxy is moving away from the Earth.

Source: Redshift Blueshift, Bender235, Wikimedia Commons

Watch the following video showing how the Doppler effect impacts light, and then answer the questions that follow.

What is happening to the behavior of the wavelengths of light as the object is moving away?

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As light is moving away from us, the wavelengths become longer, and the waves spread further apart. The light appears red because the wavelength of red on the electromagnetic spectrum is longer.

What is happening to the behavior of the wavelengths of light as the object is moving toward us?

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As light is moving toward us, the wavelengths become shorter, and the waves become more compressed. The light appears blue because the wavelength of blue on the electromagnetic spectrum is shorter.

This is the primary evidence that scientists use to theorize that the universe is expanding.

You've investigated how the Doppler effect is seen in light and sound. Now let's investigate how that looks in other applications using both light and sound.