The Wonders of the Swan

This week, explore Cygnus, the great Swan of the north.


The constellation Cygnus, the Swan, is one of the most recognizable and bright constellations visible in the northern hemisphere.  Cygnus is easily viewed from early August through late October from our latitude, here in Connecticut.

To find Cygnus over the next few weeks, go outside around 9-10 p.m.  Look directly overhead to find the bright star Vega, the brightest star in the sky this time of year, which should be very easy to spot.  Facing east, look for two additional bright stars, one to your right (southeast), the other closer to Vega, and to your left (northeast) — these are the other two stars of the summer Triangle.  The star to the left is Deneb, the brightest star in Cygnus.  To make sure you have the correct star, hold up your fist at arm's length, and spread your fore and pinky fingers.  When projected against the sky, the distance between Vega and Deneb with be about 3 times the distance between those fingers.

Cygnus is a very large constellation. Starting at Deneb, follow a line roughly southwest — to the right and upward. Placing 3 fingers side-by-side, about that distance away you should see a second bright star.  This star marks the center of a cross, with two more stars on the same line further right and up, and a crossing line marked by stars above and below this line. I've attached a diagram that should be much clearer than this description! 

The length of this cross represents the body of the swan, with Deneb at the tail, and the beautiful double star Albireo at the head.  To see Albireo as a double star you will need to use a pair of binoculars, or a small telescope.  What you should see when you find Albireo in either instrument is a striking pair of orange and blue stars.  Scientific observation of the brighter of the pair shows it to itself be a binary star, with the component stars too close to each other to be seen separately from our distance of about 410 light years.

The body line of Cygnus cuts right down the center of the region of the Milky Way most easily seen by Connecticut observers.  To notice the presence of the Milky Way, a clear dark night with little or no moon is essential.  What you will see is a slightly brighter grey in a lane centered on the body of Cygnus. 

Once you recognize the Milky Way (which can be difficult), you should be able to slowly see that it extends over a vast section of the sky, running roughly north to south this time of year.  What you are seeing as a tenuous shading of grey is actually the light of billions of stars too distant for us to see with the unaided eye.  However, pointing even the smallest pair of binoculars in this direction unveils a vastly rich assortment of stars that is truly astounding in variety and extent.

Because of the sheer number of stars located in this direction from Earth, Cygnus is the host of a great many interesting stars, star clusters, and nebulae.  Using binoculars we can view several of these objects; others require more advanced telescopes. 

The star 61 Cygnus forms a rectangle with Deneb, the star at the center of the cross, and the star forming along the lower wing.  This barely visible star is found to be a binary star in a large pair of binoculars, with a rather close separation between the components, and orbit each other once every 700 years.  61 Cygnus has a fascinating scientific history.

As early as 1792 it was noticed that this star system had an unusually large motion with respect to the stars surrounding it.  This "proper motion" demonstrates the fact that the "fixed stars" are indeed in constant motion.  Photographs taken 30 years apart show an obvious shift in position for this star.  61 Cygnus was also the first star to have its distance measured precisely using parallax — the same method used traditionally by surveyors to measure distances on Earth. 

61 Cygnus is one of the closest stars to Earth, at a mere 11 light years.  This star is also among the first known to have at least one planet — an object 8 times the mass of Jupiter was first suggested in a paper published in 1942.  The Cygnus region is also where NASA's planet-searching mission Kepler is examining over 100,000 stars to find evidence of planets.  To date, over 2,300 candidate planets have been discovered, and 74 definitely confirmed.  (Details of the Kepler mission will need to wait for a future article).

Although simply "browsing" through this area of the sky with a pair of binoculars can enthrall even a seasoned observer, there are clusters within the vast background of stars that are particularly notable.  Looking above and to the right (facing east) of the central star of the cross with a small pair of binoculars, you will come upon a small trapezoid knot of stars.  This is Messier 29 (Messier was a French astronomer, in case you were about to chuckle), a rather small but compact cluster of very young stars, partly obscured by a dark cloud of interstellar gas and dust. A second, much larger cluster is Messier 39, located about "a fist" to the left and below Deneb.

This article has already gone on too long, and I haven't mentioned any of the majestic nebulae (clouds of interstellar gas) that lie in Cygnus — see the attached photos.  But no discussion of Cygnus would be complete without mentioning Cygnus X-1. Marked by a unremarkable dim star, this location in Cygnus is one of the strongest sources of X-rays in the sky.  First discovered in 1964 using an X-ray detector carried by a sounding rocket, through careful observation of the gravity effects on the companion star, scientists concluded by 1990 that this object is a black hole of roughly 15 times the mass of the sun, with a diameter of about 55 miles! The gravitation of such a compact massive object distorts space so severely in its vicinity that light cannot escape from within, and time itself is effectively "stopped" at its surface.

I can't help but leave off with some helpful lyrics from Rush:

"I set a course just east of Lyra,
Northwest of Pegasus,
Flew into the light of Deneb,
Sailed across the Milky Way.
On my ship the Rosinante,
Wheeling through the Galaxy,
Headed for the Heart of Cygnus,
Headlong into mystery..."
(Rush, Cygnus X-1)

This post is contributed by a community member. The views expressed in this blog are those of the author and do not necessarily reflect those of Patch Media Corporation. Everyone is welcome to submit a post to Patch. If you'd like to post a blog, go here to get started.


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