Cygnus, the Swan and the Northern Cross

Cygnus, the Swan, is a large, bright northern constellation, one of Ptolemy's forty-eight, whose principal stars form the shape of a swan in flight down the length of the Milky Way, also known as the Northern Cross. Its brightest star, Deneb, marking the swan's tail, is one of the most luminous stars known and completes the Summer Triangle with Vega and Altair. In Greek myth the swan is variously Zeus in disguise or a friend of the fallen Phaethon, transformed and set in the sky. The constellation is rich in nebulae and dark rifts of the Milky Way. In astronomical tradition it is a pattern of stars rather than a zodiac sign. These are the features of Cygnus as the classical and modern traditions describe it, distinct from any astrological reading; it flies along the brightest reach of the northern Milky Way.

Cygnus borders two Hevelius constellations from 1687, Vulpecula the fox and Lacerta the lizard, the latter introduced specifically to fill a narrow, star-poor strip of sky between Cygnus, Cepheus and Andromeda that the ancient tradition had left as an unclaimed sliver between three much larger figures. The dark rifts of dust visible against the bright Milky Way background running through Cygnus are real interstellar material blocking the light of more distant stars behind them, a naked-eye-visible demonstration that the galaxy's disc contains obscuring matter as well as stars.