In Greek mythology, according to Plutarch, the 7th century BC Greek poet Alcman said that Ersa // or Herse // (Ἔρσα, Érsa, Ἕρση, Hérsē, literally "dew"), the personification of dew, is the daughter of Zeus and the Moon (Selene). Plutarch writes:
We observe this happening to the air also: it sheds dew especially at the full moon when it melts, as the lyric poet Alcman says somewhere when he talks in riddling fashion of the dew as daughter of air and moon:
such things as are nurtured by Dew, daughter of Zeus and Selene.
- Hard, p. 46; ní Mheallaigh, p. 26; Keightley, p. 55. According to Hard, "this is really no more than an allegorical fancy referring to the heavy dew-fall associated with clear moonlit nights"; while according to Keightley, calls this a "pleasing fiction" of Alcman, and says that "The moon was naturally, though incorrectly, regarded as the cause of dew, and nothing therefore was more obvious than to say that the dew was the progeny of the moon and sky personified after the usual manner of the Greeks".
- Alcman fr. 57 Campbell [= Plutarch, Moralia, 659 B = fr. 48 Bergk = fr. 43 Diehl] (see also Plutarch, Moralia 918 A, 940 A).
- Campbell, David A., Greek Lyric, Volume I: Sappho and Alcaeus, Loeb Classical Library No. 142, Cambridge, Massachusetts, Harvard University Press, 1990. ISBN 0-674-99157-5. Online version at Harvard University Press.
- Hard, Robin, The Routledge Handbook of Greek Mythology: Based on H.J. Rose's "Handbook of Greek Mythology", Psychology Press, 2004, ISBN 9780415186360.
- Keightley, Thomas, The Mythology of Ancient Greece and Italy, G. Bell and Sons, 1877.
- ní Mheallaigh, Karen, The Moon in the Greek and Roman Imagination: Myth, Literature, Science and Philosophy, Cambridge University Press, 2020. ISBN 9781108603188.
- Plutarch, Moralia. 16 vols. (vol. 13: 13.1 & 13.2, vol. 16: index), transl. by Frank Cole Babbitt (vol. 1–5) et al., series: "Loeb Classical Library" (LCL, vols. 197–499). Cambridge, Massachusetts: Harvard University Press et al., 1927–2004.
- The dictionary definition of Ersa at Wiktionary