Correct Option
The Astronomical Unit (AU) is defined as the average distance between the Earth and the Sun. This distance is approximately 149.6 million kilometers (or 93 million miles). More precisely, 1 AU is equivalent to 149,597,870.7 kilometers. It serves as a fundamental unit for measuring distances within the solar system, simplifying the comparison of planetary orbits and other celestial distances.
Incorrect Options
The average distance between the Earth and the Moon is approximately 384,400 km, which is significantly less than one Astronomical Unit and is not used as its definition.
The average distance between Jupiter and the Sun is approximately 5.2 AU, not 1 AU.
The average distance between Pluto and the Sun is approximately 39 AU, varying due to its elliptical orbit. This is also not 1 AU.