Light-year

A light-year is a standard unit of distance measurement on Earth, defined as "the distance traveled by light in the time it takes the Earth to orbit the Sun once (one Earth-year)". This definition is now deprecated on Tetro because of the known inconstancy of the speed of light. However, it is still used on Earth as the primary measure of astronomical distances due to the fact that the Grand Theory Of Relativity has not been discovered by Earth's physicists.