Luna was the name given to Earth A's moon before the Lunar Split. It was the sovereign territory of Lunar Colony Simultas, which was similarly bifurcated. The two halves are now called Luna Occidentis & Luna Orientalis.

This is why we can't have nice things.

Lunar Split

Main article: Lunar Split

Luna has been split into Luna Occidentis & Luna Orientalis, which now occupy opposite points of the original orbit.