Light-year
The distance light travels in one Julian year — about 9.461 × 10¹⁵ metres.
Definition
A light-year (ly) is the distance that light travels in a vacuum in one Julian year (365.25 days). It equals exactly 9,460,730,472,580,800 metres. Despite the name, it is a unit of distance, not time.
Formula
1 ly = 9.4607 × 10¹⁵ m = 0.3066 pc
Examples
- The Andromeda Galaxy is about 2.537 million light-years from Earth.
- Light from the Sun takes about 8 minutes 20 seconds to reach Earth — that is 0.0000158 light-years.