An enclosed room, especially one where a body meets. A chamber is a space that holds a gathering.
Latin camera (vaulted room, chamber), from Greek καμάρα (kamara, anything with an arched cover). Via Old French chambre. The word travelled from the ROOM to the private room, to the private council held in it (chamber music is music for a room, not a hall), and finally — through camera obscura, "dark room" — to the photographic camera.
The constellation's own record: lamps, lanes, and the buses between them. The chamber-music sense is the right one — a chamber is a space small enough that everyone in it can hear each other, which is what the room is for.