Parsecs and Light Years

AQA A-level PhysicsAstrophysicsLesson 9 of 24

Distances in astronomy are so large that metres are inconvenient, so two other units are used.

The light year (ly) is the distance travelled by light in a vacuum in one year:
1 ly = 3.00 × 10⁸ × 3.15 × 10⁷ ≈ 9.46 × 10¹⁵ m

The astronomical unit (AU) is the mean distance from the Earth to the Sun, 1 AU = 1.50 × 10¹¹ m.

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