From the Guide:
Red Moon: The Red Moon is visible throughout all of Glorantha, and is unique for a number of reasons. The Red Moon is the body of the goddess worshiped by the citizens of the Lunar Empire, who ascended into the sky in the Sacred Time of 1247. It is now much larger and brighter than when it first appeared, so large and bright that, alone among heavenly bodies, it is visible all day while the Sun shines. The Red Moon hangs motionless in the Middle Air directly above the Crater and the city of Glamour. The Red Moon is quite high up in the Sky, but not as high as the Sun or other planets. Its size appears almost as large as the Sun.