A light year is a measure of what?

A light-year is a unit of measurement used in astronomy to quantify distance. Specifically, it represents the distance that light travels in one year through the vacuum of space. Since light moves at a speed of approximately 299,792 kilometers per second (or about 186,282 miles per second), over the course of a year, it covers a distance of about 9.46 trillion kilometers (or about 5.88 trillion miles). This unit is particularly useful for expressing the vast distances between stars and galaxies, making it easier to comprehend scales that are otherwise incredibly difficult to visualize. Other options, such as time, mass, and brightness, do not correspond to what a light-year measures; hence, that's why they are not the correct answer.