GED Science Practice

A light-year is a unit of measurement that quantifies the distance that light travels in a vacuum over the course of one year. This concept is rooted in the speed of light, which is approximately 299,792 kilometers per second. To calculate how far light travels in a year, one would multiply the speed of light by the number of seconds in a year, resulting in a distance of about 9.46 trillion kilometers.

Using "light-year" as a measure provides a convenient way to express vast distances in space, which can often be more comprehensible than using kilometers or meters due to the immense scales involved. For example, when discussing distances between stars or galaxies, light-years allow us to convey these vast measurements effectively.

In contrast, kilometers, meters, and millimeters are all units of measurement used for measuring lengths or distances on a smaller scale, such as distances on Earth. While they can be used in various scientific contexts, they do not serve the same purpose for astronomical distances as the light-year does. Thus, "light-year" is the most appropriate choice when discussing the distance that light travels in one year.