Scientists Say: Light-year

This is the distance light travels in one year — about 9.48 trillion kilometers

This galaxy in the constellation Virgo is around 60 million light-years away. That means it took about 60 million years for its light to reach the Hubble Space Telescope, which captured this picture.

ESA/NASA

Light-year (noun, “LITE-YEER”)

This is a measurement for vast distances, like those in space. It describes the distance light travels in a single Earth year. One light-year is about 9.48 trillion kilometers (5.88 trillion miles). That’s a huge distance. In our solar system, Neptune is the farthest planet from the sun at about 4.5 billion kilometers (2.8 billion miles) from our star. That’s only 0.00047 light-year. The sun’s light reaches Neptune in just 4.2 hours. 

The stars and galaxies we see in the sky are much farther away. So stargazing is really a look into the deep past. For example, the Andromeda galaxy is around 2.5 million light-years away from Earth. Because of this distance, telescopes today see this galaxy as it was 2.5 million years ago. At that time, human ancestors had evolved, but it was long before modern humans came to be.

In a sentence

Scientists found an enormous galaxy hiding in dust 12.5 billion light-years away. 

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Carolyn Wilke is a staff writer at Science News for Students. She has a Ph.D. in environmental engineering. Carolyn enjoys writing about chemistry, microbes and the environment. She also loves playing with her cat.

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