A light-year is a unit of astronomical distance equal to the distance that light travels in one year, approximately 9.46 trillion kilometers or 5.88 trillion miles.
Examples
**Example:** The Andromeda Galaxy is about 2.5 million light-years from Earth, meaning the light we see from it today left the galaxy 2.5 million years ago. Our Milky Way galaxy is about 100,000 light-years in diameter.