Astronomy 101: From the Sun and Moon to Wormholes and Warp Drive, Key Theories, Discoveries, and Facts about the Universe (Adams 101 Series)

by Carolyn Collins Petersen

The light-year (shortened to ly) comes from multiplying the speed of light, 300,000 kilometers per second, by the total seconds in a year. The result is the distance light travels in a year: 9.5 trillion kilometers.