Cygnus the swan is flying south along the Milky Way. Although Cygnus is one of the larger and brighter constellations, I haven’t yet written a separate column on this interesting part of the sky.
The brightest star in Cygnus is Deneb, a name derived from the Arabic word for tail. Indeed, Deneb is the tail of the swan, and once you find Deneb, the rest of the constellation is straightforward to identify.
Deneb is one of the three stars of the summer triangle, the others being Vega and Altair. The summer triangle is a rather large asterism comprising three constellations and so named because it makes its first appearance in the evening sky at the beginning of summer. Now that we are almost a season beyond that, the summer triangle is nearly overhead right after dark.
To find the summer triangle, look for Vega, one of the brightest stars in the sky. Right after sunset it will be very close to your zenith point, or the point directly overhead. Twenty-four degrees to the east of Vega is the not-quite-as-bright Deneb. If you aren’t sure how far away to look for Deneb, you can easily measure the angle separating two objects by holding your fist out at arms’ length. One fist-width is approximately 10 degrees, so Deneb is almost two-and-a-half fist-widths from Vega. The third star of the summer triangle is Altair, and you can find it a bit over three-and-a-half-fist widths to the south of Vega.
To find the rest of Cygnus from Deneb, the body and very long neck of the swan are directly along the Milky Way toward the south. The head of the swan is Albireo, a little more than two fist-widths from Deneb, which puts it near the center of the summer triangle. The wings spread out from the body about a third of the way from Deneb to Albireo. Cygnus is also known as the Northern Cross, as the brighter stars form a very classical-looking cross. Albireo is the foot, Deneb is the head and the cross-piece is where the wings would be.
Albireo is one of the most beautiful double stars in the sky. A small telescope with low magnification can resolve the two stars that have remarkably contrasting colors of yellow and blue. The yellow star is the brighter of the pair, and it is itself also a binary star. I find it interesting that although Albireo is relatively bright and well-studied, it remains uncertain if the two stars are part of the same gravitational system, or if they just happen to be in the same direction in the sky.
There are many objects of interest in Cygnus, but not all are directly visible. Cygnus X-1 is an intense X-ray source that is probably a black hole that was the result of a supernova of a very massive star. Numerous exo-planets in and around Cygnus were discovered during the Kepler satellite mission. Also, many of the very diffuse glowing clouds of hydrogen gas are very large and more readily visible in long-exposure photographs than through binoculars or telescopes.
One emission nebula that is possible to see under very dark skies is the North American nebula, or NGC7000. It is just a few degrees to the east of Deneb and gets its name because it looks remarkably like the continent of North America. It is large – about the size of four full moons – so is best seen with very low magnification. A UHC (ultra-high contrast) or O[III] astronomical filter can help you see faint nebulae such as this one. These filters are made to put on telescope eyepieces, but they can also be held in front of one side of a pair of binoculars, or just held in front of your naked eye.
Another large faint object in Cygnus is the Veil Nebula, a supernova remnant that is just off the eastern wing of the swan. This can also be seen under dark skies through a pair of binoculars, and again a hand-held filter will help.
This monthJupiter and Saturn are still great binocular and telescope targets.
Besides the things to see in Cygnus, the bright Milky Way over the southern horizon hosts numerous open clusters and emission nebulae that are easily visible. One of my favorite activities is just to scan these rich star fields with very low magnification to find something that looks interesting. There is always more to see.
Mesa Verde is planning a star party Oct. 5, so maybe I will see you there.
Charles Hakes teaches in the physics and engineering department at Fort Lewis College and is the director of the Fort Lewis Observatory. Reach him at firstname.lastname@example.org.