Like the eagle in Aquila, the swan is a bird with many associations, so it seems logical to put a swan in the sky. It was Venus’ bird; the Romans sometimes called the constellation Myrtilus because of this, myrtle also being Venusian.
The Greeks, however, assigned the swan to Apollo, who had a team of them to pull his chariot. Zeus also assumed the shape of a swan to rape Leda, the queen of Sparta, who then gave birth to the Dioskouroi (and in some versions, Helen and Clytemenestra) in an egg, which must have been rather uncomfortable for her.
Phaethon and Cyncus
Another swan myth, more directly related to the constellation, involved a young man named Cyncus. He was Phaethon’s devoted friend, and after Phaethon’s doomed attempt to drive the sun-god’s chariot, Cyncus was pious enough to recover all the pieces of his friend’s body from the river it fell in so that he could bury them. (Burial was an important part of Greek belief – any bodies left unburied kept their owners’ souls from passing on to the next world.)
In return for his piety Zeus turned Cyncus into a swan and placed him in the stars. Swans had a special connection to death – the Greeks believed that swans only sang when they were about to die, which gave the birds special associations with prophecy.
Travelling the Milky Way
The Swan is right on the Milky Way, just above the rift, where the Way splits into two paths. The dark spot there consists of clouds of space dust that block the stars of the galaxy from our sight, but the split has inspired a great deal of mythology.
As the fall comes on, the Swan appears to fly down the Milky Way, as the white band moves lower in the sky. Many connect this to the myths in which the Way is the track of migrating birds. The Swan’s location near the gaps in the Milky Way may explain the Babylonian name for Cygnus: the Demon With the Gaping Mouth.
The Northern Cross
This constellation is also known as the Northern Cross, to match the one in the Southern Hemisphere. There is certainly a cross-shape in the constellation, seized on by early Christians to make the constellation their own.
A bit of fortuitous timing no doubt helped: the constellation stands almost upright in northern latitudes around sunset at Christmas Eve. Since its Classical associations were rather dubious, no doubt the new name was more pleasing to Christian sensibilities.
Cygnus can certainly be interpreted as a cross, but a closer look shows that it bears a stronger resemblance to a bird in flight, since the arms are slightly bent at the ends, as a bird’s wings are when it is flying.
Black Hole in Cygnus
The first black hole was located in Cygnus. An object called X-1 was radiating x-rays from within the constellation, and this object was the first observed thing behaving as a black hole should. (The x-rays are emitted by the matter swirling around the hole before falling into it, as water does around a drain. This is one of the few ways one can find a black hole, since they swallow everything else, including light.)
The black hole in Cygnus X-1 is a powerful emitter of x-rays, and scientists estimate it has four times the mass of our sun (which has approximately 2 194 470 x 1021 tons of mass).
The main star of Cygnus, Acrux (Alpha Cygni), is the 13th brightest star in the sky. It is also known as Deneb, from the Arabic word for tail. (While the Arabs saw Cygnus as a bird, to them it was a pigeon or hen, so the star was the hen’s tail.)
There is also a star called Deneb in Delphinus, so named because of its location at the flipper end. That star, not Acrux or Deneb in Cygnus, is the one in the Summer Triangle.
Deneb is visible from the beginning of summer, and culminates on August 1st.