Cygnus, the Swan
flies through the evening skies of summer, and is one of the three constellations that host the asterism of the Summer Triangle. This trio of first magnitude stars is led by Vega, in the constellation Lyra, followed by Deneb and Altair to complete the triangle. Deneb gets its name from the Arabic word for “tail.” And indeed, it marks the tail of the swan Cygnus as the fancied bird flies along the Milky Way. The third vertex of the Summer Triangle, Altair, is in Aquila, the eagle. Its name is Arabic, also meaning “eagle.”
Greek myth tells that the gods rewarded Cycnus, brother of Phaethon, by placing him in the sky as a swan. This was in light of Cycnus's devotion to Phaethon after the foolhardy son of Apollo fell into the river Po. You will remember the story of how Zeus struck the lad with a thunderbolt to stop his mad, chaotic dash driving the chariot of the Sun across the heavens. Cycnus repeatedly dove into the river in an effort to return his brother for a proiper burial. In so doing, he looked to the gods watching from Mount Olympus much like a swan diving for food.
Greek legend also relates that the swan is the form taken by Zeus to disguise his visits to Leda, the wife of the king of Sparta, so that he would not be recognized by his jealous wife Juno. Leda became the mother of Helen of Troy and of the twins, Castor and Pollux.
Though the constellation has been known as the Swan since ancient times, it has been at various times and places thought of as the Hen, the Ibis, or simply the Bird. In China and the Far East, it was associated with one of the Magpies who went annually to make a bridge across the river that was the Milky Way to allow the goddess to cross and meet her lover. Now, officially, the constellation is Cygnus, the Swan, while unofficially, to many it is the Northern Cross, really a most appropriate name as well.
The bill of the Swan is the very lovely double star Albireo, called by some the most beautiful double star in the sky. If you wanst to excite your friends, show them this fine example of astronomy's treasures with binoculars or a small telescope. The pair of stars, gold and blue, is separated by 35 seconds of arc and separated from us by 380 light years. The individual stars shine at magnitudes of 3.1 and 5.1.
Many other double and multiple stars are to be found among the stars of Cygnus, including a noted one, 61 Cygni. The principal partner of this multiple was, in 1838, the first star to have its parallax measured. The determination showed that the star was only eleven light years away. It is now counted among the 20 nearest stars to Earth. A third companion, 61C, was inferred by its effect on the proper motion of 61A. Accordingly, it may be a large planet of eight Jupiter masses, or it may be a small, nonluminous star, a brown dwarf. The A and B stars are red dwarfs of 5.2 and 6.0 magnitudes.
Worthy of note in this part of the sky are two Messier objects, M29 and M39. Both are open clusters of fairly bright stars, and they can be identified with binoculars.
Conrad Jung has captured an interesting scene in the central region of Cygnus. The yellowish-white 2nd-magnitude star, Gamma Cygni, about 750 light-years away and nearly 6000 times more luminous than the Sun, is surrounded by a network of bright emission and dark nebulae. Gamma Cygni, also known as Sadr, is the central star in the Northern Cross asterism. Moving from Deneb at the top of the Cross (the tail of the Swan), to Albireo at the bottom (the bill of the Swan), one finds one of the most celebrated double stars in the sky. If you want to excite your friends, show them this fine example of astronomy's treasures with binoculars or a small telescope. The stars, gold and blue, shine at magnitudes of 3.1 and 5.1. They are separated by 35 seconds of arc and separated from us by 300 light years.
Another beautiful object in Cygnus is the North America Nebula. Although best appreciated in astrophotographs, this nebula, NGC 7000, can be discerned with large binoculars or a small telescope. The resemblance to a map of the terrestrial continent is uncanny.

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