What was the historical basis for the AU definition?

Answer

The semi-major axis of Earth's orbit around the Sun

Originally, the AU was understood as the semi-major axis of Earth's orbit, derived from the observed average distance between the center of Earth and the center of the Sun.

What was the historical basis for the AU definition?

#Videos

What Does AU Mean In Astronomy? - Physics Frontier - YouTube

measurementastronomyscienceAUabbreviation