Cygnus is a familiar northern constellation with its brightest star, Deneb, marking the tail of the swan it depicts. The beautiful blue supergiant also forms part of the Summer Triangle, together with Aquila in Altair, and Lyra in Vega. Cygnus is visible to observers between +90 to -40 degrees latitudes, and can be seen in the northern hemisphere from June to December, and in the southern hemisphere in winter.
The 16th largest constellation in the night sky contains many interesting objets for astronomers to study, including galaxies, nebula, as well as ten stars with confirmed planets.
Hercules Family of Constellations
It is part of the largest grouping of constellations, known as the Hercules Family, which includes Hercules, Sagitta, Aquila, Lyra, Cygnus, Vulpecula, Hydra, Sextans, Crater, Corvus, Ophiuchus, Serpens, Scutum, Centaurus, Lupus, Corona Australis, Ara, Triangulum Australe, and Crux.
There are many myths involving Cygnus in various ways, but the most common association is with Queen Leda of Sparta, who bore two sets of twins, the first being Pollux and Helen who were both immortal, and Castor and Clytemnestra, who were fathered by Leda’s mortal husband King Tyndareus. As the story has it, Queen Leda was seduced by the god Zeus, who took on the shape of a swan during the seduction.
Cygnus is sometimes difficult to find, but one way to make locating it easier is to look for a famous asterism of stars known as the Northern Cross, which lie within the Summer Triangle. The bright star Deneb marks the head of the cross.
Cygnus contains one of the most easily recognisable asterisms in the sky, the Northern Cross, which is made up of the stars Deneb, (Alpha Cygni), Delta Cygni, Albireo (Beta Cygni), a beautiful double star, Giena (Epsilon Cygni), and Sadr (Gamma Cygni), in the centre of the group.
– Deneb (Alpha Cygni) is a blue-white supergiant (A2 Ia), located about 1,400 light years away, and with an apparent visual magnitude of 1.25, making it the 19th most luminous star in the entire night sky. It is 20 times more massive than the Sun, and a whopping 60,000 times brighter, which gives it an absolute magnitude of -7.0, making it amongst the most luminous stars discovered to date. It is expected to end its life in a supernova explosion in the next several million years.
– Sadr (Gamma Cygni); forming the heart of the Northern Cross, Sadr is a supergiant (F8 lab) star located about 1,800 light years away. Estimated to be only about 12 million years old, Sadr is twelve times as missive as the Sun, and about 150 times as big, with an apparent visual magnitude of 2.23. The name Sadr comes from the Arabic “sadr”, meaning “the chest”.
Other interesting stars in Cygnus include Gienah, Rukh, Cygni, and Albireo (Beta Cygni), located about 380 light years away with an apparent magnitude of 3.18, and arguably one of the most famous double stars due to its high colour contrast.
Notable Deep Sky Objects
Fireworks Galaxy (NGC 6946, Arp 29, Caldwell 12) is located about 23 million light years away near the border with Cepheus, and is an intermediate spiral with an apparent visual magnitude of 9.6.
North America Nebula (NGC 7000, Caldwell 20) is located about 1,600 light years away, with an apparent visual magnitude of 4.0. Its low surface brightness makes it all but invisible unless at least large binoculars are used to observe it.
Cygnus X-1 is located about 6,100 light years away, and is perhaps the best known X-ray source, since it was the first potential back hole to be discovered. The object is estimated to have about 8.7 solar masses, which is puny by black hole standards, but it is considered to be too small to be anything else but a black hole.
The two minor meteor showers associated with Cygnus are the Kappa Cygnids, and the October Cygnids.
The Kappa Cygnids; this long-running shower is not noted for its high maximums, or even its regularity. The shower runs from about July 26th, to about September 1st, and largely coincides with the more productive Perseids shower in the first week of August which makes it easy to miss. However, the Kappa Cygnids seems to peak around August 18th, but do not expect to see more than 8-10 meteors per hour during maximum.
The October Cygnids; these appear to run from about September 22nd to October 10th, with a peak around October 6th/7th. Few meteors have been detected visually, and maximum hourly rates rarely exceed 10.