Ersa was the daughter of Zeus and Selene (the moon). Her name means 'dew' (erse), which was believed to have been caused by the moon - compare the lines from A Midsummer Night's Dream where the Fairy sings: Ί do wander everywhere, Swifter than the moone's sphere; And I serve the fairy queen, To dew her orbs upon the Green', and where Oberon speaks of 'young Cupid's fiery shaft Quench'd in the chaste beams of the wat'ry moon'. Ersa's name was also doubtless metaphorical to denote a young and tender being, one born in the freshness of the morning.