Luna herself embodies the Moon - unlike a mere Incarna, a Celestine literally is its affiliated concept. To destroy Luna the Celestine in the Umbra would destroy the moon itself. Luna's Umbral home is in the Aetherial Realm, which may or may not blend into a Penumbral reflection of outer space. Journeying to the Umbral moon is a most serious quest in Werewolf, but one often necessary to take. It is only from Luna that one can acquire Moonsilver and Pathstones.