- Astronomical Unit. A unit of distance used to measure orbits and trajectories within the solar system. An Astronomical Unit is the average distance between the Sun and Earth. One AU is roughly equal to 149,600,000 km (92,956,000 mi.). To give you an idea of the distance involved, if you drove a car at 160 kilometers per hour (100 miles per hour) for twenty four hours a day, it would take just over 106 years to travel one AU.
The writer's dictionary of science fiction, fantasy, horror and mythology. 2014.