White areas on the left are when the moon is full, black areas on the right is when the moon is dark. The calendar starts on the first of january, at the outside, and goes clockwise around the spiral, finishing at 31st December near the centre.
Each month is marked with a particular colour, to make the months easier to see. The horizontal line on the right marks the start of a new moon. If a month crosses that line twice, the second moon is a blue moon according to some definitions
