Lesson 6 of 6

Light years

Goal: Use the light year as a unit of distance.

Puzzles for this lesson

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The pale band of the Milky Way across a starry night sky, above a dark hill with one tree

The stars are so far away that the kilometre is too small a unit to be handy. Distances to the stars are measured in light years.

  • A light year is the distance that light travels in one year. It is a distance, not a time.
  • Nothing travels faster than light. It crosses space at 300 000 km every second. In a year that adds up to more than 9 million million km.
  • Light from far away is old. It takes about 8 minutes to reach us from the Sun, about 4 years from the nearest star beyond the Sun, and millions or billions of years from other galaxies.

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Key words in this lesson

Star A huge ball of hot gas that gives out its own light

Year The time the Earth takes to orbit the Sun once

Light year The distance that light travels in one year

For teachers: AQA 3.7.2