The two halves of the Indian lunar month are named for their end points: Purnima, the full moon, and Amavasya, the dark one.

Most Hindu festivals are pinned to one or the other — Holi and Guru Purnima and Buddha Purnima on the full, Diwali and Mahalaya on the dark. Northern and southern India even start the month at different ends of the cycle, so the same lunar month carries two different names depending on which state you are in.