Each phase of the Moon has it's own special meaning. All the witches are moon watchers, and very much so:)
The details of the triptych: Waxing Moon, Waning Moon, Full Moon.
_________________ Oh yes, one more thing: she is riding her broom the brush end first because this is the way the REAL witches are riding their brooms. We like to say that this style of riding is an original one, that this is the way the witches used to ride broom by the end of the 17th century... You see, the broom represents both the Goddess and the God, the union of male and female energies... figure it out...;) And yes, that means that Harry Potter is riding broom facing backwards! :P