Constellation of the Month: Cygnus, The Swan.

by Mark S Deprest
Printed in Reflections: July, 2001.

The constellation Cygnus

This is without a doubt my favorite constellation, for a number of reasons, but the most important one is probably; this constellation is the source of my active participation in astronomy, that’s another story entirely. This month’s story is about Love, Honor, Foolishness and Friendship. It’s a story that explains the reason we see the Milky Way as a faint path across the night sky.

Cycnus was a devoted friend of Phaethon, the mortal son of Helios, the charioteer of the Sun. Phaethon was a bold and head strong teenager, and like most teenagers, he thought he knew more than his “Old-Man.” One night his bold nature got the better of him, and despite the advice of his friend Cycnus, and the warnings of his father, Phaethon took out the family car for a bit of a joy ride. The trouble was, the family car was the Sun Chariot and its horsepower was provided by real horses, Phaethon realized very quickly that his joy ride was a mistake, but it was too late. The horses that pulled the Sun Chariot were strong and wild, and only the strength of Helios could control them. Phaethon’s wild ride took him dangerously close to the vault of the heavens and threatened to singe the earth and destroy the inhabitants of both. Cycnus pleaded with Jupiter to stop this destruction, and with all of creation endangered, Jupiter sent a thunderbolt toward the rampaging chariot and its occupant. With a terrible explosion Phaethon was thrown from the chariot and the fiery steeds were stopped long enough for Helios to gain control and guide them back to their stables. Phaethon, being mortal could not survive the force of a thunderbolt and fell to earth like a shooting star, his charred and lifeless remains landed in the river Eridanus.

Cycnus could not leave his friend to the creatures of the river to feed on, and wanted to give Phaethon a proper burial. Cycnus dove repeatedly into the river to gather the charred remains of his friend. Jupiter, watching this selfless display of devotion was moved, and when Cycnus had completed his task of love and honor. Jupiter decided to give Cycnus a gift of immortality and changed his name to Cygnus and him into a glorious swan. This swan would be placed forever in the heavens amidst the scorched path of Phaethon’s disastrous ride, the Milky Way.

There are other stories that may be related to this constellation, early Christians saw it as the Cross of Calvary and it is also known as the Northern Cross. But the story related here is by far a personal favorite.

Transit at Midnight of Alpha Cygni: August 21st

This constellation is stretches across 804 square degrees of one of the richest areas of the Summer Milky Way. It reaches from almost 19 hours in the west to 22 hours in the east and runs from +27 degrees to +60 degrees north declination. The stars that make up the main figure of Cygnus are first, second and third magnitude gems that stand out easily against the ethereal glow of the Milky Way back drop. To list a good representation of the objects worth examining in Cygnus took 30 pages of descriptions, charts, drawings and photos in George Kepple’s and Glen Sanner’s The Night Sky Observer’s Guide [go here for the complete reference]. We obviously don’t have that kind of room in this newsletter, so, what follows are a few of my favorites, and a suggestion to spend no less than one full evening in feathered regions of Cygnus. I can almost guarantee you won’t be disappointed.

Things to Check Out in Cygnus

Multiple Star Systems

Albireo, Beta Cygni, STF43, ADS 12540

RA (J2000): 19h 30m 43.29s dec: +27d 57m 34.9s
Included in the Astronomical League’s certificate list of 100 double stars.
Included in the Saguaro Astronomy Club’s list of 110 best multiple stars.
Components show no relative motion.
Colorful double star.
Distance: 380 light-years
Component A: magnitude +3.1
Component B: magnitude +5.1
Separation AB: 34.4” at position angle 54 degrees
Discovered by Struve in 1832.
Despite the wide separation, the two stars are thought to be physically associated.
The best-known of all colored double stars, and considered by many to be the finest in the sky.
The colors are yellow or “topaz” for the primary, and blue or greenish for the companion.

61 Cygni, STF2758, ADS 14636

RA (J2000): 21h 06m 52.19s dec: +38d 44m 03.9s
Included in the Astronomical League’s certificate list of 100 double stars.
Included in the Saguaro Astronomy Club’s list of 110 best multiple stars.
Visual binary star.
Included in Michael R. Feltz’s list of the widest visual binaries. Orbital elements and diagram available on Richard Dibon-Smith’s website (http://www.dibonsmith.com/).
Distance: 11.4 light-years
Component A: magnitude +5.4
Component B: magnitude +6.0
Separation AB: 30.3” at position angle 150 degrees
The famous “Flying Star”. Its unusually large proper motion (5.22” a year at PA 52) was first noticed by Piazzi in 1792, although the first measurement as a double was by Struve in 1830.
Bessel chose 61 Cygni in 1838 for the first successful measurement of the distance of a star using its annual parallax. At 11.4 light-years, this is the fourth nearest star to the Sun, only Alpha Centauri, Sirius, and Epsilon Eridani being closer.
Sometimes said to look yellowish or orange, which fits the spectral classes. The system consists of two orange dwarfs.
There is a dark third component known as 61 Cygni C, with a mass only 8 times that of Jupiter.

31 (Omicron) Cygni and 30 Cygni, STF50, ADS 13554

RA (J2000): 20h 13m 37.90s dec: +46d 44m 28.8s
Included in the Astronomical League’s certificate list of 100 double stars.
Included in the Saguaro Astronomy Club’s list of 110 best multiple stars.
Optical double, colorful double star.
Distance: A 1350 light-years B 1700ly C 720ly
Component A: magnitude +3.8
Component B: magnitude +6.7
Component C: magnitude +4.8
Separation AB: 101” at position angle 173 degrees
Separation AC: 338” at position angle 323 degrees
An interesting triple group, although the stars are certainly not physically associated. Star C in this data is actually numbered 30 Cygni in Flamsteed’s catalogue.
31 Cygni A has a noticeable yellow color, while B and C (30 Cygni) are bluish.
31 Cygni A is an eclipsing binary of the Algol type numbered V695 Cygni. It ranges between magnitudes 4.9 and 5.3, with a period of 10.4 years. The orbit is very nearly edge-on to us, so that the eclipse of the companion is almost total. It is preceded and followed by a period of partial eclipse as the companion passes behind the extended atmosphere of the primary. Each atmospheric eclipse lasts for 2.5 months, and the total phase for 63 days. The next atmospheric eclipse is due to begin in mid-October 2003.

Delta Cygni, STF2579, ADS 12880

RA (J2000): 19h 44m 58.44s dec: +45d 07m 50.5s Visual binary star.
Included in Michael R. Feltz’s list of the widest visual binaries.
Orbital elements and diagram available on Richard Dibon-Smith’s website (http://www.dibonsmith.com/).
Distance: 171 light-years
Component A: magnitude +2.9
Component B: magnitude +6.5 variable
Separation AB: 2.5” at position angle 221 degrees
First observed by Struve in 1826 (WDS) or 1830 (Burnham).
This is a particularly tricky double for a small telescope because the secondary lies on the first diffraction ring of the primary.
Muirden (1988) says some people suggest looking during twilight.
Star B is variable between magnitudes 6.5 and 8.5 (approximately).

Deep Sky Objects

The area of the sky we are looking into is also known as the Cygnus Star Cloud and is one of the most visually beautiful parts of the northern Milky Way. When you examine this area you are looking down the length of our spiral arm where is begins to curve around the center of our galaxy. So, you might expect to see clusters and nebulae of all types and that is exactly what you find, here are some of my favorites.

NGC 6819

R. A. 19h41.3000m Dec: +40d 10.99’
Angular diameter: 5.0 arc minutes
Distance: 2200 parsecs
Age 3,400,000,000 years
Open cluster, very large, very rich in stars, stars
150 stars (11-15 mag).
Brightest star is magnitude 11.0

NGC 6866

J2000 RA: 20h03.7m dec: +44 00’
Angular diameter: 6.0 Arc minutes
Distance: 1200 parsecs
Age 230,000,000 years
Open Cluster, large, very rich in stars, considerably compressed
50 stars (10 - 13mag)
Brightest star is magnitude 10.0

NGC 6826, Blinking Planetary, PK83+12.1

NGC 6826

J2000 RA: 19h44.8m dec: +50 31’
Planetary nebula, bright, pretty large, round.
Star in middle of image is 11th magnitude
Angular diameter 27”X24”
Visual magnitude, integrated over entire object: 9.8

IC5146, Cocoon Nebula

IC5146

J2000 RA: 21h53.4m dec: +47 16’
Maximum diameter: 540 arcseconds
Distance: 1000 parsecs
Age 230,000,000 years
Brightness level: 1 (1=brightest, ..., 6=faintest)
Emission nebula, pretty bright, very large, irregular figure.
A 9.5mag star is located in the middle of the image.

NGC 6910

J2000 RA: 20h23.1m dec: +40 47’
Angular diameter: 7.0 Arc minutes
Distance: 1650 parsecs
Age 10,000,000 years
Open Cluster, pretty bright, pretty small in angular size, poor, pretty compressed.
20 stars (10-12 mag)

NGC 6913, M29

NGC 6913

J2000 RA: 20h23.9m dec: +38 32’
Distance: 1250 parsecs
Age 10,000,000 years
Open Cluster, poor, little compressed, stars large and small in angular size
About 20 stars (mags 9-12), brightest star is magnitude 9.0
Angular diameter 7.0’

NGC 6960, Veil Nebula (western part), Supernova Remnant

NGC 6995

J2000 RA: 20h45.7m dec: +30 43’
Angular diameter 70’X6’
Magnitude: 7.0
Brightness level: 4 (1=brightest, ..., 6=faintest)
Reflection nebula, very much remarkable, pretty bright, considerably large, extremely irregular figure
52 Cygni involved

NGC 6992 and NGC 6995, Veil Nebula (eastern part), Supernova Remnant

NGC 6960

NGC 6992

(NGC 6992 left and NGC 6995 right)

J2000 RA: 20h56.4m dec: +31 43’
Angular diameter 60’X8’
Magnitude: 7.0
Brightness level: 4 (1=brightest, ..., 6=faintest)
Reflection nebula, very much remarkable, extremely faint, extremely large, extremely extended, extremely irregular figure, bifurcated

NGC 7000, North America Nebula

NGC 7000

J2000 RA: 20h58.8m dec: +44 20’
Angular diameter 120’X10’
Magnitude: 4.0
Brightness level: 4 (1=brightest, ..., 6=faintest)
Reflection nebula, faint, most extremely large, diffused nebulosity
Open Cluster NGC 6997 involved

NGC 7092, M39

J2000 RA: 21h32.2m dec: +48 26’
Distance: 270 parsecs
Age 270,000,000 years
Open Cluster, very large, very poor, very little compressed
(7-10 mag) Brightest star is 7.0mag
Angular diameter: 31.0’

Credits

All Images on this page were downloaded from the Sloan Digital Sky Survey.

Constellation of the Month: Cygnus, The Swan.