A green moon is one of two celestial bodies orbiting the planet Alternia in Universe A. While by all appearances it seems to be a natural satellite, it was not present in the pre-scratch iteration of the universe.
At least part of the planet's surface is covered in a hazy green city, though who if anyone inhabits this city, aside from one “strange and powerful man”, is a mystery. It is sometimes erroneously believed that the Felt's mansion resides on this moon, though in fact it is located on Alternia's surface.
History[]
One candidate for the origins of the green city.
The green moon's exact origins, such as whether it was imported from some distant part of Universe A, created "from scratch", or came to be in some other way, are not known. One of the planets in Caliborn's session, however, was home to a black city with many of the same buildings seen on the green moon. This might suggest that, after conquering the black planet, Lord English painted it in the color of his sister's blood “AS A TOKEN OF [HIS] RUTHLESS TRIUMPH” and took it with him for use in his future conquests.
Doc Scratch's apartment[]
The remains of Scratch's apartment in the 
.
The magic timepiece originating as a boon in Caliborn's session was eventually homed on the green moon. Viewing and travel between Doc Scratch's home on the green moon and the home of Andrew Hussie was also facilitated by a mysterious fifth wall. When Scratch began spouting off his ancestor fanfic, Hussie broke through this window to enter the apartment and deal with the situation himself.
After Universe A's destruction, Scratch's residence formerly located on the green moon was among the debris in the resulting that remained relatively intact; Spades Slick, of course, couldn't let this stay true for long, and escaped with the Felt through the magic clock into the Furthest Ring.
In Hiveswap Friendship Simulator and Pesterquest (Dubiously Canon)[]
Doc Scratch hosted the player in his apartment during the events of the Friendsim Epilogue and the beginning of Pesterquest: Volume 1 , during which time the player took the time to catch up on the events of Homestuck on Scratch's computer.
The player again returns to the apartment during the climax of
Pesterquest:
Volume 14 , wandering in through a blue corridor between metaphysical realities called the Afterw@rd. Here, they witness a bully identifying themselves as the Director chase Hussie into a closet with a wolf head in it,[citation needed] seemingly implying the attic where Hussie was briefly trapped while writing Homestuck was in fact a room in this apartment.