Cygnus is a familiar northern constellation with its brightest star, Deneb, marking the tail of the swan it depicts. This 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
Cygnus is part of the largest grouping of constellations, known as the Hercules Family, which contains 19 individual constellations, including 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 the second being 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 lies within the Summer Triangle, with the bright star Deneb marking the head of the cross. From northern locations, the Summer Triangle can be seen during some part of the night the whole year round, but appears prominently overhead during the summer months.
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 with an apparent visual magnitude of 1.25, ranking it as the 19th most luminous star in the entire night sky. It is 20 times more massive than the Sun, a whopping 60,000 times brighter, and has an absolute magnitude of -7.0, making it amongst the most luminous stars yet discovered. Deneb is around 10 million years old, and is expected to eventually become a red giant before ending its life in a supernova explosion several million years in the future. Its name Deneb comes from the Arabic word for “tail”.
– Sadr (Gamma Cygni), the constellation’s second brightest star, is a blue-white supergiant (F8 lab) found 1,800 light years from our solar system with a visual magnitude of 2.23. It is estimated to be only 12 million years old, and has around 150 times the Sun’s radius, and twelve times its mass. Sadr forms the heart of the Northern Cross, and its name comes from the Arabic word for “the chest”.
– Gienah (Epsilon Cygni), the third brightst star in Cygnus, is an orange giant star (K0 III) situated 73 light years distant of magnitude 2.48. It is around 11 times bigger than our Sun, and has 62 times its luminosity. The name Gienah comes from the Arabic for “wing”.
– Albireo (Beta Cygni) is a binary star located 380 light years away that shines with a magnitude of 3.18. The system consists of a primary yellow star with a fainter blue companion, with the striking color contrast making it one of the most beautiful double star targets for stargazers. Albireo is found at the head of the swan, and is sometimes referred to as the “beak star”.
Other interesting stars in Cygnus includes the blue supergiant Sigma Cygni; the blue-white dwarf Iota Cygni; the white dwarf Nu Cygni; the yellow giant Kappa Cygni; and the orange giant Eta Cygni.
Notable Deep Sky Objects
Lying along the plane of the Milky Way means Cygnus is rich in deep-sky objects, with the constellation including two Messier objects, namely M29 and M39, both of which are open star clusters consisting of around 50 and 30 stars respectively. Other objects of interest includes:
– 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 galaxy with an apparent visual magnitude of 9.6. Over the last 100 years, there have been nine supernovae observed in NGC 6946.
– Cygnus X-1, located about 6,100 light years away, is a bright X-ray source that led to the first potential black hole being discovered. It consists of a blue star and a black hole orbiting each other, with the gas pulled off the star by the black hole subsequently heating up and radiating as X-rays. The object is estimated to have about 8.7 solar masses, which is puny by black hole standards, but is considered to be too small to be anything else but a black hole.
The constellation also includes a number of nebulae including the Pelican Nebula, the Crescent Nebula, the Veil Nebula, and the North America Nebula (NGC 7000), which 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.
The two minor meteor showers associated with Cygnus are the Kappa Cygnids, and the October Cygnids.
The Kappa Cygnid is a long-running shower not noted for its high maximums, or even its regularity. The shower runs from around July 26th to 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. Meanwhile, the October Cygnids runs from September 22nd to October 10th, with a peak around October 6th/7th when maximum hourly rates rarely exceeds 10 meteors per hour.