illuminationAngle

The angle of the moon illumination relative to earth. The moon is waxing if the angle is negative, and waning if positive.

By subtracting LunarPosition.parallacticAngle from illuminationAngle, one can get the zenith angle of the moons bright limb (anticlockwise). The zenith angle can be used do draw the moon shape from the observer's perspective (e.g. the moon lying on its back).