What is a light year used to measure?

A light year is a unit of measurement that describes the distance that light travels in one year. Given that light moves at approximately 299,792 kilometers per second (or about 186,282 miles per second), this distance amounts to about 9.46 trillion kilometers (or about 5.88 trillion miles) over a year. Thus, light years serve as a convenient way to express vast distances in space, making it easier to conceptualize how far away stars and galaxies are from Earth. This makes option C the correct answer, as it specifically relates to measuring distance rather than other aspects like speed, brightness, or mass.