A light-year is a unit of distance that measures how far light travels in one year. Since light moves at an incredible speed of about 299,792 kilometers per second (or about 186,282 miles per second), a light-year equals approximately 9.46 trillion kilometers (or about 5.88 trillion miles). This measurement is commonly used in astronomy to express distances between stars and galaxies. For example, the nearest star system to Earth, known as Proxima Centauri, is about 4.24 light-years away. This means that light from Proxima Centauri takes over four years to reach us. Using light-years helps astronomers convey vast distances in a more understandable way.