How Far is a Light Year?

X-Ray image of Proxima Centauri. Image credit: Chandra

A light year is a standard of measurement used by astronomers to describe huge distances in the Universe. The nearest star is 4.22 light years away. The center of the Milky Way is about 26,000 light years away. But how far is 1 light year? A light year is the distance that light travels in a single year. And light travels fast.

1 lightyear is 9,460,730,472,580.8 kilometers.

Need some other measurements? A light year is 5,878,625,373,183.6 miles. And a light year is 63,241 astronomical units (1 astronomical unit, or AU is the average distance from the Earth to the Sun).

But a light year isn’t the largest measurement tool astronomers have. That’s a parsec. 1 parsec = 3.26156 light years.

We have written several articles about measuring distance for Universe Today. Here’s an article about the speed of light, and an article about a device that makes radio waves go faster than the speed of light.

If you’d like more information on light years, here’s an article about what a light year is and how it’s used, and here’s a cool video that shows you how far a light year is.

We’ve also recorded an episode of Astronomy Cast about different tools for measuring distance in the Universe. Listen here, Episode 10: Measuring Distance in the Universe.