Capricornus Constellation

Mythology

Capricornus, the Sea Goat, is one of the most ancient constellations, with its peculiar hybrid form — the foreparts of a goat and the tail of a fish — attested in Babylonian astronomy as far back as the 21st century BCE, representing the god Enki (Ea), lord of the primordial waters. In Greek mythology, the figure is often identified with Pan, the goat-footed god, who in some accounts leapt into the Nile to escape the monster Typhon, transforming himself into a goat-fish in the process. According to Hyginus, Zeus placed Pan in the sky to commemorate the gods' collective flight from Typhon into Egypt, where they disguised themselves as animals. The hybrid sea-goat form is one of the most striking examples of an ancient Babylonian constellation figure surviving essentially unchanged through Greek and Roman transmission into the modern era. At the time of Babylonian astronomy, the winter solstice occurred in Capricornus, which is why the latitude of minimum solar elevation is still called the Tropic of Capricorn. The constellation contains no first-magnitude stars; Deneb Algedi (Delta Capricorni), the brightest star, is a variable eclipsing binary at magnitude 2.85.

Sources: Aratus Phaenomena 283-299; Hyginus Astronomica 2.28; Eratosthenes Catasterismi 27.

Overview

Capricornus is one of the 88 constellations formally recognised by the International Astronomical Union (IAU). It occupies 414 square degrees of sky in the southern hemisphere sky, best visible at latitudes between +45 and -90 degrees in September. The constellation belongs to the Zodiac family of constellations. Its Latin genitive is Capricorni, the form used when naming stars within the constellation — for example, the brightest star Deneb Algedi may appear in catalogues as Alpha Capricorni or similar. The IAU standardised the boundaries of all 88 constellations in 1930 under the direction of Eugène Delporte, using straight lines of right ascension and declination to eliminate the ambiguities of earlier variable-boundary systems.

Notable stars

The brightest star in Capricornus is Deneb Algedi. Individual stars within Capricornus are conventionally named using Bayer designation — Greek letters followed by the Latin genitive of the constellation name (Capricorni) — introduced by Johann Bayer in his 1603 star atlas Uranometria. Flamsteed numbers (numeric designators followed by Capricornus) were added by John Flamsteed in his 1712 catalogue. Variable stars, double stars, and deep-sky objects within the Capricornus boundary are catalogued by the IAU with the abbreviation Cap.

History and mythology

The figure of Capricornus appears in the classical astronomical tradition. Ptolemy included this constellation in the Almagest (c. 150 CE), the definitive ancient catalogue of 48 constellations, which formed the foundation for Islamic, medieval European, and Renaissance astronomy. The constellation's figure and mythology were transmitted through works such as Aratus's Phaenomena, Eratosthenes's Catasterismi, and Hyginus's Astronomica. See the Mythology section above for the full narrative.