Light-years and cosmic distances
A light-year is a unit of distance that measures how far light travels through space in one year. Despite the word "year" in its name, it is not a measure of time but of distance. Light-years matter because the universe is so vast that traditional distance measurements become impractical. Distances between stars are expressed in light-years, galaxies span thousands to hundreds of thousands of light-years across, and the most distant objects are billions of light-years away. This unit helps us understand the enormous scale of space and how far we must look—and how far back in time—to observe distant objects in the cosmos.
Sources
- en.wikipedia.org: “A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly 9460730472580.8 km, which is approximately 9.46 trillion kilometres or 5.88 trillion miles.”
- en.wikipedia.org: “Despite its inclusion of the word "year", the term is a unit of distance, not a unit of time.”
- en.wikipedia.org: “Galaxies themselves span from a few thousand to a few hundred thousand light-years in diameter, and are separated from neighbouring galaxies and galaxy clusters by millions of light-years. Distances to objects such as quasars and the Sloan Great Wall run into the billions of light-years.”