Up here in the northern half of the planet we will be seeking a pair of perennial favorite galaxies and an obscure open cluster in the northern portion of Ursa Major. Our southern friends will be focusing on the beautiful constellation of Centaurus. Within the centaur’s realm, they will be hunting down a trio of fine objects, an open cluster, planetary nebula and diffuse nebula.
(Northern Celestial Hemisphere)
Messier 81 / NGC 3031 (Ursa Major, spiral galaxy, mag=6.9, size=26.9'x14.1', SBr=13.2):
This large and bright galaxy, along with nearby Messier 82, form one of the most observed and imaged galactic duos in the northern sky. M81 was discovered by Johann Bode in 1774 and has thus is sometimes referred to as “Bode’s Nebula. It is the brightest and largest member of the M81 Group of Galaxies, which is a cohesive group of about 34 galaxies in Ursa Major and Camelopardalis.
Located about 10° northeast of mag 1.8 Alpha Ursae Majoris (Dubhe), one can use a line drawn from the “Dipper” stars mag 2.4 Phad (Gamma UMa) through Dubhe to the northeast to aid in locating this beautiful galaxy. Depending upon one’s sky quality this object can be easily within reach of binoculars. Even in small apertures one may pick up a broadly brighter core region surrounded by a diaphanous oval disk. . With increasing aperture and particularly under darker skies, one may glimpse some very elusive spiral structure that may be more inferred rather than directly seen. Its large disk may appear mottled hinting at its elusive spiral structure due to the transition between light (spiral arm) and dark (dark lanes between). Imagers can truly use the skills of their art to pull out this behemoth’s beautiful structural detail.
Messier 82 / NGC 3034 (Ursa Major, spiral galaxy, mag=8.4, size=11.2’x4.3’, SBr=12.5):
The second largest member of the M81 Group is this disrupted spiral that is often referred to as the “Cigar Galaxy” because of its thin, elongated visual appearance. Known as a starburst galaxy because of its high level of stellar formation, this nearly edge-on spiral has most likely been disrupted through interaction with nearby M81. It is also known as Arp 337 from Dr. Halton Arp’s Catalogue of Peculiar Galaxies. Just like M81, it was discovered by Johann Bode in 1774.
This beauty is only about half a degree north of M81 and they can easily be seen within the same visual field of view at lower magnifications. While dimmer in visual magnitude than its neighbor, it has a higher surface brightness because of its smaller angular size. It too may be picked up in binoculars and small apertures, appearing as a thin, fairly large elongated glow. With increasing aperture, and again with darker skies, one may notice a darker lane bisecting its disk near the center. One may also glimpse some extensions protruding outward, perpendicular to the major axis, from the central portion of its elongated disk. As with most galaxies, the imagers among us can use their skills to reveal much more of its structural intricacy, rending it in beautiful detail.
NGC 3231 (Ursa Major, open cluster, mag=10.0, size=9.5’):
This object is a bit of an obscure one. It lies along the line from Dubhe to M81, nearly 6.5° northeast of the bright star. This object is relatively unknown in terms of the riches of Ursa Major. In fact, in the Revised New General Catalogue (RNGC), it is deemed non-existent based on its appearance in DSS images. Discovered in 1832 by John Herschel, he described it as a "cluster, considerably large, poor, a little compressed, stars from 10th to 12th magnitude.”
Visually, this cluster is not what I would call impressive. Nonetheless, I would not call it non-existent as it is listed in the RNGC. The cluster lies immediately north of the mag 7.9 star HD 90318, and to my eye it consists of two sub-groups of stars within its field separated by a mostly starless lane or void. Take a look at the below annotated DSS2 image to get a sense of this object. You can pretty much take it to the bank that this one will not impress you, but John Herschel spotted it, noted it and so should you!
(Southern Celestial Hemisphere)
NGC 3766 (Centaurus, open cluster, mag=5.3, size=15.0’):
This beautiful cluster is informally known as the Pearl Cluster, and is located not quite 1.4° north of mag 3.1 Lambda Centauri. This object was discovered by Nicolas-Louis de Lacaille during his time in South Africa (1751-52). He described it as "three faint stars in nebulosity." However, he was only using a ½ inch telescope at 8x. It was also observed by James Dunlop and John Herschel, both of whom saw it for its true nature.
Visually it is a spectacular cluster, with a dense central region. As aperture increases so does the number of stars one can discern. But even in small apertures it can be a thrilling object with a plethora of stars shimmering atop a backdrop of gauzy unresolved star light. In darker skies it can be easily seen naked eye and even in binoculars it is intriguing.
NGC 3918 (Centaurus, planetary nebula, mag=8.2, size=16.0”x16.0”, SBr=5.7):
This very well known object is nicknamed the “Blue Planetary” for a good reason. Its prominent blue color is legend. In fact, it was first recorded as a “fine blue star”, by James Dunlop in 1826. Unfortunately he apparently he missed its non-stellar nature. John Herschel is credited with its discovery in 1834, describing it as "perfectly round; very planetary; color fine blue; .very like Uranus, only about half as large again and blue."
This planetary is truly a gorgeous object. It blue color is robustly apparent through the eyepiece as one observes its small round disk. The central star is a very dim mag 15.7, and beyond visual observation within the diffuse disk of the planetary. The nebula’s disk exhibits sharply defined edges against the background field and appears evenly illuminated. Its surface brightness is high, making it an excellent target even for smaller apertures. But it is the intensely blue color that is the most striking feature of this object. It truly is a stunning piece of celestial art work.
IC 2944/2948 (Centaurus, emission nebula, mag=4.2, size=45.0’x40.0’):
This well known and often imaged nebula complex is catalogued in two parts, though in all likelihood it could be a singular physical structure. In fact, the RCW and Gum catalogues both label these under a single identifier. In terms of the Index Catalogue, what is labeled as IC 2944 is typically referred to as the Lambda Centauri cluster as this bright 3.1 mag star is center point for its delicate and wispy nebulosity. The larger portion just to the east and southeast of IC 2944 is catalogued as IC 2948. Both were discovered on a photographic plate in 1904 by Royal Frost. However, he did not seem to notice the open cluster sitting in the middle of IC 2448, catalogued later as Collinder 249.
Under dark skies this can be a delicate and fascinating object to observe visually, particularly when using either a narrow-band nebula filter or an O-III line filter. Those who do AP can come up with some truly amazing images of this large complex. A lot of what you will see will depend on the quality of your skies. But even from a suburban area I was able to tease out nebulosity surrounding the cluster Cr 249 using an 80mm while observing on a business trip near the equator.
Informally, depending upon the source, one or the other or even both can be found labeled as the “Running Chicken Nebula”. I have to admit, this moniker is totally lost on me, and apparently many others as well from what I’ve read. To my eye, looking at images of this complex, there is nothing to suggest a relationship to a fowl of any type. In fact, when I look at the below attached DSS image, my mind conjures up a vague sense of the North American Nebula, with heavy emphasis on the western part of the continent. I see a Gulf of Mexico area, and even nearby IC 2872 could be construed (in a positional sense) to represent the Pelican Nebula adjacent to the famous North American Nebula. I see that, but I do not see a chicken! (smiley)
Okay folks, there you have it for this month. I lay this challenge before you to use as you see fit. I hope you will take up the mantle and purse them to the extent possible. Some you likely have seen or imaged before, but perhaps I have given you something new to add to your nightly cruises. Good look and first and foremost, have fun!
