Stars - CCEAHigher tier: How far is one light year?

Remember that one light year is the distance light travels in one year.

Distance = speed x time

Speed of light = 300,000,000 m/s

Speed of light = 3.0 x 10⁸ m/s

Time = 1 year

Time = 365 x 24 x 60 x 60

Time = 31,536,000 s

Distance = 3.0 x10⁸ x 31,536,000

Distance = 9.46 x 10¹⁵ m

1 light year = 9.46 x 10¹⁵ m

One light year is a distance of 9.46 x 10¹⁵ m.

Summary

• Distances to stars and galaxies are so enormous that they are measured in light years.
• A light year is the distance light travels in one year.
• A light year is a distance not a time.
• One light year is a distance of 9.46 x 10¹⁵ m

Example

Alpha Centauri is 4.4 light years away from us. How far is that in metres?

Answer

One light year = 9.46 x 10¹⁵ m.

4.4 light years = 4.4 x 9.46 x 10¹⁵.

4.4 light years = 4.2 x 10¹⁶ m

Alpha Centauri is 4.2 x 10¹⁶ m away from us.