Light-year
A light-year is the distance light travels in a year, about 9.46 trillion kilometres.
A light-year is a measure of distance, not time. It is how far light, the fastest thing in the Universe, travels in one year: about 9.46 trillion kilometres, or about 63,000 astronomical units.
Light-years are used for distances between stars. The nearest star system to the Sun, Alpha Centauri, is about 4.4 light-years away. The Milky Way galaxy is roughly 100,000 light-years across. By contrast, sunlight takes only about 8 minutes and 20 seconds to reach Earth.
The outer edge of the Oort Cloud, the vast shell of comets around the Solar System, may stretch about 1 to 2 light-years from the Sun, almost halfway to the nearest star. Interstellar objects such as ʻOumuamua and Borisov had travelled across distances of many light-years before they passed through our Solar System. Some presolar grains in meteorites came from stars that may have been many light-years away.
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Level: Beginner Ages 7 and up