The Moon is a celestial body and the natural satellite orbiting Earth. In the adventures of Popeye, the Moon is an unusual place, home to several alien races who keep their existence as obscure as possible, making many believe that the Moon is uninhabited and uninhabitable. The better-known races populating the Moon are the Moon Goons and the Moon Rocks, led by Alice the Goon's grandfather and King Joe Granite respectively.
The Sea Hag's ship, the Black Barnacle (or the Sea Hag herself) seems to have some sort of influence over the Moon (or at least its appearance to those near her who are seeing the Moon), as whenever she is sailing the sea at night, the Moon turns a blood red color to signify her presence, similar to a Blood Moon lunar eclipse. Prior to the events of "Plunder Island", the Sea Hag raided countless ships for centuries, whisking away their crews on the nights of the Red Moon, making the latter a horrifying omen for sailors unfortunate enough to have experienced it or heard tales of it.