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The light-year
Age 14 · Astronomy
A light-year is the distance light travels in one year. Because space is vast, looking at faraway stars means seeing light that left them long ago.
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In the picture
- A star: the source of the light.
- A glowing point in the trail: light moving through space.
- Earth: the blue planet where the light arrives.
- A telescope: an instrument that gathers light from the sky.
Examples
- Sunlight takes about eight minutes to reach Earth.
- If a star is ten light-years away, its light left ten years ago.
Key takeaways
- A light-year measures distance, not time.
- Looking far into space is looking back in time.
Quiz: The light-year (Age 14)
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What does a light-year measure?
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What does looking far into space mean?
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What is a light-year?
The answers, each with its explanation, are in the app. This lesson has left the free week, so its quiz is part of the subscription.
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