Asterism (astronomy) - Former Asterisms

Former Asterisms

Argo is a special case. Argo Navis, ("the ship Argo"), was, by far, the largest of Ptolemy's constellations. Starting with Lacaille in his Coelum Australe Stelliferum (1763), it became common to refer to its various parts as the Keel, the Poop Deck, and the Sails. In the 1930 IAU arrangement, Argo was deemed too large, and these old sectional asterisms were recognized as official constellations (Carina, Puppis, and Vela), thereby turning Argo, as a whole, into an asterism.

The Southern Cross is not an asterism, but merely a variation on the meaning of Crux. Crux was an asterism when Bayer created it in Uranometria (1603) from stars in the hind legs of Centaurus. It was given constellation status in 1930, thereby mutilating the Centaur.

Centaurus had been reduced in size once before. Lupus was originally considered to be merely a sectional asterism (as an unspecified Wild Beast in the Centaur's grasp). Hipparchus split it off in the 200s BC, and Ptolemy's list confirmed its independent status.

In its original figuration, Leo included a spray of faint stars pictured as the tuft in the Lion's Tail which stretched straight out from its body. Antedating even Ptolemy by centuries, Conon of Alexandria created the asterism "Berenice's Hair" commemorating his queen in 243 BC. Following Tycho's acceptance of Coma, Bayer recorded it and refigured the Lion. The IAU confirmed Coma's status as a constellation.

Even so venerable a constellation as Libra was once merely an asterism. Until the middle of the first millennium BC, the Zodiac consisted of only eleven constellations. The biblical reference to "the eleven stars" (Genesis 37:9) is more accurately "the eleven asterisms/constellations (of the Zodiac)." At the time, Scorpius' claws were pictured as extending to Zubenelgenubi, "the southern claw" and Zubeneschamali, "the northern claw" (Alpha and Beta Librae). Later, when Virgo was reimagined as Astraea, the goddess of justice, the Claws became a set of scales held in her hand. By Ptolemy's day, Libra had become an independent constellation, unconnected with either of its neighbors. Still, the names of its stars reflect the time when it was the asterism of "The Claws" and its figuration is that of the old sectional asterism within Virgo.

The groups named here were sectional asterisms that have been promoted to constellation status. For a list of proposed constellations that were not accepted as anything beyond asterisms, and are now considered obsolete, see Former constellations.