Summer Constellation Spotlight: Cygnus

Cygnus is the 16th-largest constellation, prominent even in urban skies. But if you’re lucky enough to view Cygnus from a dark-sky location, the Swan seems to soar over a flowing river of stars—the Northern Milky Way. Cygnus’ brightest star, Deneb, makes up the tail end of the Swan. Deneb is part of the famous Summer Triangle—an easily recognizable asterism of three bright stars—along with Altair in Aquila and Vega in Lyra. Cygnus is close to other prominent constellations, including Cepheus, Draco, Lacerta, Lyra, Pegasus, Sagitta, and Vulpecula.

Home to many interesting celestial objects, including double stars, emission and planetary nebulae, and supernova remnants, Cygnus offers plenty to explore. Let’s take a look at some of the most popular targets.

Sadr, or Gamma (γ) Cygni, is the second brightest star in Cygnus, shining at magnitude +2.2. It’s an easy target for observers because it resides at the intersection of the Northern Cross’ heart, surrounded by bright areas of the Milky Way.

At the head of Cygnus is the beautiful double star, Albireo, or Beta Cygni—always a popular target during Summer star parties. Some Southern California stargazers have dubbed Albireo the “UCLA Double Star.” With side-by-side yellow and blue stars, it reminds locals of the university’s colors. A small telescope or a high-powered binocular will split this colorful pair. Albireo was once considered a true binary star system, but there has never been evidence of orbital motions between the two stars. Astronomers now believe the two stars making up Albireo are a visual double, not a binary system.

61 Cygni, also known as the “Flying Star,” is a faint double star with orange dwarf stars of magnitudes of +5.21 and +6.03. In 1838, Friedrich Bessel used the trigonometric parallax method to calculate 61 Cygni’s distance from Earth—one of the first such measurements ever taken. In images taken over several years, 61 Cygni shifts its position in the sky with respect to distant stars surrounding it.

Messier 39 is a large but loosely structured open cluster with a magnitude of +5.5. You can see M39 with the naked eye from a dark-sky location, but it is well-resolved in binoculars or a telescope. M39 is about 9 degrees northeast of Deneb and only about 800 lightyears away. Charles Messier added this cluster to his catalog in 1764, but French astronomer Guillaume Le Gentil is often credited for its discovery.

NGC 6960 and NGC 6995 are components of the Veil Nebula and part of the Great Cygnus Loop, a huge shell of ionized gas and dust remnant from a supernova explosion over 10,000 years ago. Its two brightest structures are the Western and Eastern Veil. The Western Veil resembles a “Witch’s Broom,” while the Eastern Veil resembles an interwoven rope. You can observe the Veil Nebula in binoculars from a dark sky. Use a telescope with low power to examine its rope-like structure; it appears to go on and on. An Oxygen III filter will darken the sky, increase contrast, help bring out its interwoven structure, and make it easier to see.

Next to Cygnus’ brightest star, Deneb, is the famous North American Nebula (NGC 7000), an emission nebula that resembles the North American continent—including the Gulf of Mexico and Central America. Its large surface measures 3 degrees north to south and 2.3 degrees east to west—more than four times the size of the full moon! Discovered by Sir William Herschel in 1786 in Slough, England, the North American Nebula is visible to the naked eye in only dark, transparent skies as a hazy patch just east of Deneb. Use binoculars to locate this amazing celestial continent. You’ll find the Pelican Nebula (IC 5070) to the right of the North American Nebula. With its unmistakable Pelican-like appearance, it also belongs to the same interstellar cloud of ionized hydrogen. Both nebulae are prominent in deep-sky images.

The Cocoon Nebula (IC 5146) is a beautiful red and blue emission nebula approximately 4000 light years away. With a magnitude of +7.2, it is well within the reach of backyard telescopes. You’ll find a cluster of baby stars deep within the nebula with a compact floral appearance. In the center is a central star formed about 100,000 years ago, which gives this nebula its luminosity.

The Crescent Nebula or Dividing Cell Nebula (NGC 6888) is a striking emission nebula with an appearance like its namesake. The brightest portion of its arc is prominent on its north end, while the eastern side shows a sharp curve toward its south end. With a magnitude of +7.4, the Crescent Nebula is an interesting object. Many Milky Way stars shine through it, which you can see in astroimages. Astronomers believe its central star, WR 136, may go supernova in a few million years.

NGC 6826 is a well-known planetary nebula, often called the “blinking planetary” because it appears to blink as you observe it. As you gaze directly at its central star, its brightness overwhelms the eye, causing it to fade. When you use averted vision, the nebula mysteriously reappears. The variation between the two observation techniques causes the “blinking” effect. Try it and see for yourself!

Cygnus is also home to a powerful X-ray source called Cygnus X-1. A visible star appears to be a companion in orbit around the X-ray source, which scientists believe may be a black hole stripping matter away from the visible star.