CYGNUS, the Swan. (Pronounced SIG-nuss)
This is one of the larger of the old constellations, to which seventeen stars were assigned by the Greek astronomer Ptolemy in 150 AD. It represents a swan flying down the Milky Way. There are many legends about swans, including that of Zeus who visited Leda, wife of King Tyndareus of Sparta disguised as a swan. This mating resulted in Pollux, one of the heavenly twins. Cygnus has also been identified with Orpheus, who was turned into a swan and placed next to his harp (Lyra) in the sky. The Arabs depicted this constellation as a hen.
Difficult to see from New Zealand is the Veil Nebula, the remains of a star that exploded as a supernova around 60,000 years ago. Cygnus also contains a bright X-ray source Cygnus X-1, that is probably matter from an accretion disc spiralling into a black hole.
To find this constellation look low to the north in the evening sky, and find the bright star Deneb. Deneb will not be visible from southern New Zealand, in which case look below a position between the bright star Altair in Aquila, the Eagle, and the Great Square of Pegasus, for the large cross shape going into the horizon.
The northern hemisphere's "Summer Triangle" is marked by the bright stars Altair, Vega and Deneb.
Chart showing Cygnus as seen on the northern horizon, mid September about 10 pm.
The levels of the horizon at Auckland, Wellington and Invercargill are shown.
Some stars and interesting objects in the Constellation
α Cygni (Deneb, meaning tail) is a magnitude 1.3 blue-white super giant star 3229 light years away.
β Cyg (Albireo) is one of the sky's showpiece double stars. It consists of two gloriously contrasting yellow and blue-green stars, the brighter is a yellow giant of magnitude 3.1, while the companion is of magnitude 5.1. They can be separated through good binoculars, and are a beautiful sight in amateur telescopes. The 3.1 yellow star is 386 light years away. The bright star is also a close pair of stars but these are unlikely to be resolved in amateur telescopes.
γ Cyg (Sadr, breast) is a magnitude 2.23 yellow supergiant star 1524 light years away.
δ Cyg appears a magnitude 2.9 bright pale yellow star, but actually is a pair of stars, difficult to resolve because they are very low for New Zealand. They lie 171 light years away.
ε Cyg (Gienah, wing) is a magnitude 2.46 yellow giant star 72 light years away.
μ Cyg is a bright yellow pair of stars, first measured in 1780 by William Herschel, the discoverer of Uranus. The star magnitudes are 4.83 and 6.22 and they orbit each other about every 700 years. They lie 73.1 light years away. The stars require a moderate telescope to split them. There is a wide unrelated 7th magnitude binocular companion.
ο1 Cyg (31 Cyg) may be the most beautiful binocular double in the sky, consisting of orange and turquoise companion stars of magnitudes 3.8 and 4.8, 1353 light years away. It is very low and difficult from New Zealand.
61 Cyg is a famous star. It was the first star to have its parallax measured, by the German astronomer Wilhelm Bessel in 1838. This is the slight difference in position of the star compared to background stars from opposite sides of Earth's orbit. It is a nearby star 11.4 light years away, consisting of a pair of stars with magnitudes 5.2 and 6.05.
M 39 is a large bright open cluster discovered in 1764 by Messier. It needs a large field and low magnification to be seen properly, and is suitable for binoculars and small telescopes, although it is very low even for north New Zealand stargazers.
NGC 7000, the well-known very large "North American" nebula is 3° east of Deneb, in the rich Cygnus region of the northern Milky Way. If it were higher it would be easy to see in binoculars or a rich field telescope.
Cygnus only partly rises as seen from New Zealand. At its highest, the brightest star Deneb, is about 8° above the horizon as seen from Auckland and less than 4° from Wellington. Places further south than latitude 45° will not see the star rise at all. From Auckland the star is above the horizon for nearly 6 hours, but only 4 hours from Wellington.
Deneb is due north from Auckland and Wellington at about 11.30 pm (NZST) mid August, 9.30 pm mid September and 8.30 pm (NZDT) in mid October. After mid October evening twilight will prevent observation of the constellation.