Get facts about astronomy. Learn about the moon, sun, stars, planets, galaxies, and more.

The light year is a unit of length used to measure vast distances, like between galaxies.
The light year (ly) is a unit of length that is the distance light travels in a vacuum in one Earth year. One light year is approximately 9.46 trillion kilometers (9.46 x 1012 km) or 5.88 trillion miles (5.88 x 1012 mi). The light year is used to describe distances to stars without having to use very […]

What Is a Light Year? Definition and Examples

Astronomers believe it's possible for a moon to have a moon of its own.
We all know planets orbit stars and moons orbit planets. Have you ever wondered whether a moon can have a moon of its own (a submoon)? Theoretically, the answer is yes, but there is a good reason why we haven’t discovered any submoons around moons in our own solar system. […]

Can a Moon Have a Moon?