Astronomy

How to Identify the Constellation of Cygnus in the Night Sky



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The constellation Cygnus, the Swan, is located in the northern sky between the constellations Lyra (the Harp), Draco (the Dragon), Cepheus (the King), Lacerta (the Lizard), and Vulpecula (the Little Fox). Cygnus is one of the few constellations that bears some resemblance to its name. Its brightest stars form an asterism, or pattern, better known as the Northern Cross. In Greek mythology, Cygnus corresponds to the swan in the story of Zeus and Leda, in which Zeus disguised himself as a swan, seduced the queen, and became the father of Pollux and Helen of Troy.  

This article will discuss the easiest ways for sky watchers to find Cygnus then explore some of the stars and deep sky objects located in this constellation.  

When and Where to Look

Cygnus is visible at some time of night nearly all year long to observers in the Northern Hemisphere. Cygnus rises in the northeast after midnight during spring. It can be seen overhead during the summer months in the early evening and in the northwestern sky throughout autumn. By late December, Cygnus sets a couple of hours after sunset. For most of winter, Cygnus can be seen shortly before sunrise then after midnight by early spring.

Stars   

Two of the most noticeable stars in Cygnus are Deneb and Albireo. Deneb, which means tail in Arabic, is a blue supergiant star that marks the tail of the swan or upright of the Northern Cross. Deneb is the only first magnitude star in Cygnus, and is 19th among the 20 brightest stars visible in the night sky. In terms of absolute brightness, however, Deneb is one of the brightest stars in our galaxy, shining over 60,000 times brighter than our sun. Deneb is so massive that it radiates as much light in a single day as our sun does in a century.

The reason Deneb does not appear brighter is due to its immense distance from Earth, estimated at 1,600 light years. A light year is the distance light travels in one year, or approximately 5.8 trillion miles. In other words, Deneb is so far away that the light reaching your eyes left the star not long after the Visigoths sacked Rome in the year 410 AD.

Albireo, meaning the hen’s beak, marks the head of the swan or base of the Northern Cross. To the naked eye, Albireo is a third magnitude star, somewhat dimmer than the three stars marking the Swan’s body. A small telescope reveals Albireo to be a blue and gold double star. Astronomers estimate these two stars to be 380 light years from Earth. Albireo is a physical double, meaning its component stars are locked into orbit around each other by mutual gravitational attraction.

Several deep sky objects in Cygnus are visible through a telescope. They include the Veil Nebula, a supernova remnant; three emission nebulae, the Crescent Nebula, North America Nebula, and Pelican Nebula; as well as the Messier objects M29 and M39, both of which are open star clusters. The Milky Way runs directly through Cygnus and is easily visible through binoculars or a small telescope.

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