Noctua (Latin: owl) was a constellation near the tail of Hydra in the southern celestial hemisphere, but is no longer recognized. It was introduced by Alexander Jamieson in his 1822 work, A Celestial Atlas, and appeared in a derived collection of illustrated cards, Urania's Mirror. Now designated Asterism a, the owl was composed of the stars 4 Librae and 54–57 Hydrae, which range from 4th to 6th magnitude.
The French astronomer Pierre Charles Le Monnier had introduced a bird on Hydra's tail as the constellation Solitaire, named for the extinct flightless bird, the Rodrigues solitaire, but the image was that of a rock thrush which had been classified in the genus Turdus, giving rise to the constellation name Turdus Solitarius, the solitary thrush. It has also been depicted as a mockingbird. The boundaries of the constellation were defined as longitude 0° to 26°30' and from the ecliptic to 15° S.
- Bakich, Michael E. (22 June 1995). The Cambridge Guide to the Constellations. Cambridge University Press. pp. 45–47. ISBN 978-0-521-44921-2.
- Kanas, Nick (5 June 2012). Star Maps: History, Artistry, and Cartography. Springer Science & Business Media. pp. 185–6. ISBN 978-1-4614-0917-5.
- O'Meara, Steve (14 June 2007). Herschel 400 Observing Guide. Cambridge University Press. p. 192. ISBN 978-0-521-85893-9.
- Ian Ridpath (1988). Star Tales. James Clarke & Co. p. 151. ISBN 978-0-7188-2695-6.
- Ian Ridpath's Star Tales – Noctua
- Obsolete Constellations: Noctua, the owl
- Entry for Noctua in A glossary: or, Explanation of the principal terms used in the sciences of astronomy and geography; with a description of the principal stars and constellations of the heavens. by Robert Goodacre. Fifth edition (1828).