In the oldest Indian version the Moon is a bowl of soma, the drink of immortality, and it wanes because the gods and the ancestors take a draught each night.

The Shatapatha Brahmana works it out in detail: fifteen deities drink on fifteen successive nights and the Moon empties, then the Sun refills it. Soma is the drink, the plant and the Moon all at once, and the same word turns up as the Persian haoma. It is the tidiest mythological account of the phases anybody produced.