From the introduction:
Glorantha is not a sphere, hanging in space, orbiting a sun. It is a lozenge of earth floating along the river of time, surrounded by additional planes of existence that accompany it on its journey. Above the world is the Sky Dome, separating the sky from the land, and, in this bowl, hang the stars, the planets and Glorantha’s rarely seen Blue Moon (which is a goddess, not a satellite).
Player orientation material for the short-lived Mongoose Living Glorantha campaign.