What is the average distance referred to in one Astronomical Unit (AU)?

One Astronomical Unit (AU) is defined as the average distance from the Earth to the Sun. This standard measurement is approximately 93 million miles or about 150 million kilometers. The AU is a fundamental unit in astronomy, particularly useful for expressing distances within our solar system. It provides a convenient way to compare distances between celestial objects, like planets, which are generally measured relative to the distance of the Earth from the Sun.

The other options refer to different measurements: the distance from the Earth to the Moon is significantly less than an AU, typically around 238,855 miles (or about 384,400 kilometers). The distance to Mars varies greatly depending on the relative positions of the two planets, but it averages around 140 million miles (or 225 million kilometers) at opposition. The distance across the Milky Way galaxy is vast, estimated to be around 100,000 light-years, which is far greater than any distances measured in AU. Hence, the choice of the distance from the Earth to the Sun accurately describes the value of one AU.