A light-year is a unit of distance that measures how far light travels in one year. Since light moves incredibly fast—about 186,282 miles per second (or 299,792 kilometers per second)—it can cover vast distances in just a year. For example, when we say that the nearest star, Proxima Centauri, is about 4.24 light-years away, it means that light from that star takes 4.24 years to reach us. Using light-years helps astronomers understand the immense scale of the universe. Instead of using miles or kilometers, which can be hard to comprehend over such vast distances, they use light-years to make it easier to grasp how far away objects like galaxies or black holes are from Earth.