Here's why:

* Light-year: A light-year is the distance that light travels in one year. It's a massive unit of distance, used to measure the vast distances between stars and galaxies.

Other astronomical units of distance include:

* Astronomical Unit (AU): The average distance between the Earth and the Sun.

* Parsec: A unit of distance used for measuring the distance to stars.

* Kiloparsec: A unit of distance equal to 1000 parsecs.

* Megaparsec: A unit of distance equal to 1 million parsecs.

Let me know if you want to know more about any of these units!