Cormanthyran Moon Magic( Lost Empires of Faerûn, p. 7)
You have mastered the ancient elven techniques of drawing power from Sehanine Moonbow's light.
Knowledge (history) 4 ranks, ability to cast 3rd-level spells,
When you cast a spell under moonlight, your effective caster level increases by 2. This feat provides no benefit when the moon is not visible (during the day, underground, during a new moon, or the like).