two uncommon verbs describe the moons act of getting larger and smaller. Waxing - getting larger Waning - getting smaller So 'the moon, waxing towards full' means 'the moon, which was getting larger as the month passed, and was now almost a 'full moon' The meaning of Pulsed is separate. Consider the meaning if we remove the subclause: Starlight showered and the moon pulsed against the night sky. Pulsed, in the context of light, means quickly alternated between bright and dim. I don't quite understand the authors meaning, but that is the literal meaning of the sentence.