I just realized that I have no idea what Homestuck cosmology is like anymore.
The Furthest Ring is apparently the space outside the Skaia session. I.e. you have Skaia, then Prospit ring, LoXaX ring, Derse ring, Meteor ring, Furthest Ring.
However, Universe Frogs contain multiple sessions - Alpha and Beta Kids sessions are contained in a single Frog, and presumably the two Troll sessions are both in their Frog. (And presumably the Cherub session is in a third Frog, and so on by species...)
However, the Green Sun is ignited in the Furthest Ring, and is visible to the Kids and Troll sessions, (and presumably others, since Guardians are apparently a pretty matter-of-fact thing...) indicating that the Furthest Ring is outside the Frogs, instead of the sessions.
I guess that considering the Furthset Ring is supposed to make a mockery of time and space, this should be expected, but I still find myself wondering where the Horrorterrors are now, to figure out who's the most likely suspect for Plumbthroat.
And that's all assuming that the Sburb sessions take place in the same dimension as the universe frogs... If not, then the green sun energy is crossing dimensional boundaries to empower the Guardians, which... isn't that far-fetched, I guess.