# Light-year

Also called: ly, parsec, pc.

The distance light travels in a year: about 9.5 trillion kilometres. A parsec is 3.26 light-years.

Distances in space are so vast that astronomers measure them by light's travel time. Light takes 1.3 seconds from the Moon, 8 minutes from the Sun, 4.2 years from the nearest star, 1,300 years from the Orion Nebula and 2.5 million years from the Andromeda Galaxy — so you see each as it was when that light set off.

**Examples:** [alpha-centauri](https://astropilot.space/object/alpha-centauri.md), [M42](https://astropilot.space/object/M42.md), [M31](https://astropilot.space/object/M31.md)

**Related:** [Galaxy](https://astropilot.space/glossary/galaxy.md), [Milky Way](https://astropilot.space/glossary/milky-way.md)

From the AstroPilot astronomy glossary: https://astropilot.space/glossary/light-year