The ell is a unit of length and originates from historic England and uses the symbol ell.
The ell usually measured 45in or 1.143m but was origally a "cubit" - which was the length from your elbow to the tip of your fingers and literally translated from the word "arm". It was mostly used in the tailoring world when buying and selling textiles.
Although now obsolete, the word "ell" still survives in the English word "elbow".
The astronomical unit is a unit of length and is used in the Astronomical system of units and denoted by the symbol au.
It represents the average distance between the Earth and the Sun which is approximately 150 million kilometres (or 93 million miles).
It's used mostly to express distances within our Solar System.