The two types of moons.
A Dilithium Moon is a moon that provides the resource Dilithium. Dilithium is used in warp cores and is the main resource in the games. Dilithium is mined by all races, although Species 8472 converts dilithium into biomatter. There are 2 types of dilithium moons. The first has a blue tint and has a set amount of dilithium. It grows smaller as more dilithium is mined from it. The second has a purple tint, and has an infinite amount of dilithium. These are valuable as you will not run out of dilithium when they are mined. Dilithium can be traded for metal, and can be bought by latinum. While all non-8472 ships need dilithium to be built, not all need metal.