Cygnus - The Swan

Cygnus is one of the major constellations in the northern hemisphere's summer sky, best seen from June through November. To find Cygnus, draw a line from the bright star Deneb (the tail) to Albireo (the bill). The wings are formed by two stars at right angles to this line. Cygnus is also known as the Northern Cross.

History and Mythology

Cygnus has been recognized since ancient times. It represents the bird into which Zeus transformed himself to seduce Leda, the Queen of Sparta. Leda laid an egg which hatched the twins Castor and Pollux.

Another myth tells us that Phaeton, the young son of Helios, begged his father to drive the chariot of the Sun across the sky. After much begging, his father agreed. Phaeton lost control of the horse, and his chariot burned a wide streak across the sky, which became the Milky way. Zeus was forced to kill Phaeton to stop the destruction. His body tumbled into a river. Phaeton's best friend Cygnus came to the riverbank every day and cried for his friend. To ease his pain the gods placed Cygnus in the sky, where he took the form of a swan.

Notable Stars

Deneb is a blue-white giant star at the tip of the Northern Cross. It is the 19th brightest star in the sky, and a distance of 1,400 light-years, is more than 54,00 times the Sun's luminosity, making it one of the most luminous stars in the Milky Way. Due to precession, Deneb was a pole star 18,000 years ago, appearing 7 degrees from the North Celestial Pole. It will be one again around the year 9800 A.D.

Gamma Cygni, or Sadr, is a magnitude 2.2 star lying prominently at the center of Cygnus's cross. It is also a white supergiant lying 1500 light years away; its name comes from an Arabic phrase that means "the hen's breast." Epsilon Cygni, or Gienah, is a yellow-orange giant 72 light years away.

Beta Cygni or Albireo is one of the most famous double stars in the sky. It consists of a gold 3rd magnitude star with an indigo 5th magnitude companion, separated by 34 arcseconds. The Albireo system is about 340 light years away and has an orbital period of at least 75,000 years.

A much fainter double star is 61 Cygni, a 5th- and 6th- magnitude pair of orange dwarf stars appearing 34 arcseconds apart. This pair, with an orbital period of 650 years, is the 12th nearest star system, only 11.4 light years away. 61 Cygni was the first star to have its distance measured, by Frederich Bessel in 1838, using the trigonometric parallax method.

Chi Cygni is a Mira-type variable star that can reach magnitude 3.5 for some time during its 400-day variation period, and then plummet to magnitude 14.

Clusters, Nebulae, and Galaxies

M 29 is a 7th-magnitude open cluster just south of Sadr, the middle star in the cross. It contains about 20 stars. M 39 is a 5th magnitude open cluster northeast of Deneb. It contains about 25 stars from the 6th magnitude, and it is at a distance of 800 light-years.

Cygnus contains the supernova remnant known as the Cygnus Loop, or the Veil Nebula. It is the remains of a huge shell of gas thrown off by an ancient supernova explosion. This object can be barely seen with good binoculars on a dark night, and makes a good target to scan over with low power in larger telescopes.

The North America Nebula, NGC 7000, is a complex cloud of bright glowing regions and dark obscuring matter. Its shape resembles the continent of North America. It can be observed in binoculars on dark nights. Nearby is the Pelican Nebula, IC 5070, which is another large, but fainter, nebula. Another large region of nebulosity, IC 1318, surrounds the star Gamma Cygni, and is known as the Gamma Cygni nebula.

The Cocoon Nebula, cataloged as IC 5146, is a strikingly beautiful emission nebula located about 4,000 light years away. The Crescent Nebula, NGC 6888, is an emission nebula about 4,700 light years away.

Cygnus contains two planetary nebulae of interest for amateur telescopes. NGC 7027 is a small, relatively bright planetary nebula best viewed with high magnification. NGC 6826 is commonly referred to as the "blinking planetary", although many other nebulae can exhibit such "blinking". Stare at the nebula's central star until its brightness overwhelms the eye, and causes the nebula to fade. When you then glance away, the planetary's disk will reappear. This alteration between direct and averted vision of the planetary's nucleus thus causes the nebula to blink.

Cygnus also includes the powerful X-ray source Cygnus X-1. There is a visible star near Cygnus X-1 that appears to be a companion in orbit around the X-ray source. Many scientist think that Cygnus X-1 is a black hole, which is striping matter away from the visible star.