What unit of distance in astronomy equals approximately three light-years?

The correct answer is parsec, which is a fundamental unit of distance used in astronomy. A parsec is defined as the distance at which one astronomical unit subtends an angle of one arcsecond. It is equivalent to approximately 3.26 light-years, which aligns closely with the question indicating a distance of about three light-years. This makes the parsec a convenient unit for measuring vast distances between stars and galaxies, allowing astronomers to convey distances in a way that reflects the astronomical scale.

In contrast, light-years and astronomical units are both measures of distance but are not equivalent to a parsec. A light-year is the distance that light travels in one year, and while an astronomical unit is the average distance from the Earth to the Sun, it is much smaller than a parsec, being about 93 million miles (or about 8.3 light-minutes). A kilometer, while a common unit of distance on Earth, is vastly too small to be useful in astronomical contexts.