Cygnus: Zeus, Leda and the great cross of the Milky Way
Zeus turned into a swan to seduce Leda, Cycnus mourning Phaethon, the star Deneb and the Northern Cross: myths of the constellation of Cygnus the Swan.
On summer nights, along the pale river of the Milky Way, a great cross-shaped figure stretches out. Its wings are spread, its neck reaches southwards and its tail is marked by a bright star. It is Cygnus, which the Greeks simply called Ornis, “the bird”, and which only later was identified with the white creature dear to Apollo and Aphrodite. Around it mythology has woven several stories, all tied to metamorphosis.
Zeus and Leda
The most famous version attributes the constellation to one of the loves of Zeus. The god fell for Leda, wife of Tyndareus, king of Sparta, and to approach her he took the form of a swan. According to the myth, Leda laid one or two eggs, from which were born Helen, Clytemnestra and the twins Castor and Pollux, called the Dioscuri. Ancient sources debate which of these children were fathered by Zeus and which by Tyndareus.
Another tradition, already known to the poems of the epic cycle, tells that Zeus pursued Nemesis, goddess of just retribution, who changed into various animals to escape him; when she became a goose, the god became a swan. The egg born of that union was then entrusted to Leda. The theme of Leda and the swan enjoyed great success in art: it was treated, among others, by Leonardo da Vinci and Michelangelo, whose works are known to us mainly through copies.
The grief of Cycnus
Ovid, in the Metamorphoses, offers a different origin. Cycnus, king of the Ligurians and a kinsman of Phaethon, saw the young man plunge into the river Eridanus after losing control of the chariot of the Sun. In despair he wandered along the banks mourning him, until the gods turned him into a swan. Mindful of the heavenly fire that had killed his friend, the new bird avoided the sky and preferred to stay on the water.
Other authors linked Cygnus to Orpheus, who after his death was said to have been changed into this bird and placed in the sky beside his lyre, the neighbouring constellation. The swan was indeed, in Greek tradition, a musical animal: it was believed to sing most sweetly shortly before dying, a belief Plato recalls in the Phaedo and from which the expression “swan song” derives.
Deneb, Albireo and the Summer Triangle
The brightest star of the constellation is Deneb, a name that comes from Arabic and means “tail”. Although it appears less bright than others, it is a very distant supergiant, among the most luminous stars known in absolute terms. At the swan's head lies Albireo, which through a telescope turns out to be a pair of stars of different colours, one golden and one blue, among the most admired by observers.
Deneb forms with Vega, in Lyra, and Altair, in Aquila, a large triangle clearly visible on summer evenings, which modern astronomers call the “Summer Triangle”. The cross-shaped pattern of the constellation has also earned it the name Northern Cross, in contrast to the Southern Cross visible in the other hemisphere. In 1627 Julius Schiller even proposed renaming it the Cross of Saint Helena, without success.
Cygnus thus brings together stories of desire and stories of mourning: the god who transforms himself to love and the friend who is transformed to grieve. In both cases the animal becomes the sign of a passage between two natures, human and divine, earthly and heavenly. Even today, on summer nights, its outline seems to fly along the Milky Way, as if following the course of a river.