This month we will be following along (for the most part) the primary plane of our own galaxy, the Milky Way, sampling some of its riches. The northern summer and southern winter is rife with delightful nebulae of various types and myriad star clusters of both the open and globular variety. You will see we are heavily weighted into the objects of Charles Messier for this edition, as he has some of the finest in the skies within his short list. They make excellent visual and imaging objects and are frequently re-visited even by the most experienced members of our hobby simply because they are that good. So let’s get into this month’s selections for your viewing, sketching and/or imaging pleasure. I hope you like the journey whether you’re seeing these for the first time or the hundredth; they never get old.
Northern Celestial Hemisphere:
Messier 27 / NGC 6853 (Vulpecula, planetary nebula, mag=7.1, size=8.0’x5.7’, SBr=11.0):
This stunning planetary was discovered by Messier in 1764 and is the first planetary nebula discovered. It was independently discovered by Caroline Herschel in 1782 during only her second sweep as she was looking for comets.
Nicknamed the “Dumbbell Nebula” due to its bi-lobed interior structure, it is one of the premiere objects sought out during the northern summer nights. Bright and large (for a planetary) it is one of the first such objects (along with M57) viewed by beginners who are building their observing and/or imaging skills. With its higher surface brightness it is easy to pick up with all sizes of instruments, and clearly recognizable as a non-stellar object. With moderate aperture and scrutiny, it reveals its tell-tale dumbbell, or apple core or hourglass (whichever you prefer) interior structure. The planetary visually responds very well to a narrow-band nebula filter, as well as an O-III line filter. Its mag 13.5 central star may be glimpsed, plus there are several imposed foreground stars that may be picked up as well. This is truly an amazing object.
Messier 57 / NGC 6720 (Lyra, planetary nebula, mag=8.8, size=1.4’x1.0’, SBr=8.9):
The famous “Ring Nebula” is another northern summer staple for observers. Conveniently located nearly half way along a line from Beta Lyrae (Sheliak) to Gamma Lyrae (Sulafat), it is viewable by apertures small to large, though small scope will not reveal much detail. At a minimum it appears as a small ghostly orb, but with more aperture it turns into a smoke ring, with a strong annular structure and gauzy veil filling in its donut hole. With larger scopes, with a keen eye and steady seeing its mag 15.4 central star may be glimpsed and poses an excellent challenge.
Like most planetaries it responds well to both narrow-band nebula and O-III line filters. It was discovered by Messier on 31 January 1779 while looking for Bode’s Comet (the great comet of 1779). Sometimes we see references to discovery by Antoine Darquier in mid-February 1779, but his was an independent discovery and Messier deserves full credit. Regardless, give this perennial favorite a careful study and see just how much detail you can pull out. For those with larger aperture and darker skies, see if you can pick up the small barred spiral galaxy IC 1296 (mag=14.0, size=1.1'x0.9'; SBr=13.8) just 4’ northwest of M57. It presents an excellent challenge.
Messier 71 / NGC 6838 (Sagitta, globular cluster, mag=8.1, size=7.2’, class=11):
Sagitta the celestial arrow lies in a very rich Milky Way field between Vulpecula and Aquila. It is home to this very loosely structured globular cluster. Discovery credit for this object goes to Philippe de Chéseaux in the 1745-46 timeframe. Whether this is an unusually dense open cluster or a particularly loose globular cluster has been the subject of speculation. Initially classified as the former, a study in the 1970s determined it was actually more akin to the later type of object.
Regardless of all the confusion surrounding its true physical nature, it is indeed a curious object worthy of our attention. This beautiful cluster appears as a hazy concentration within a rich Milky Way field using smaller apertures. But as one increases aperture and magnification, it resolves nicely into a concentrated scatter of stars, well detached from the field and overlaying a hazy backdrop of deeper members. While it is not the rival of some of the more majestic globulars well known to observers and imagers, it is still an entrancing object that should be studied more closely, and I encourage you to do so.
Southern Celestial Hemisphere:
Messier 8 / NGC 6533 (Sagittarius, bright nebula, mag=5.8, size=90.0’x40.0’):
The infamous “Lagoon Nebula” is a thing of beauty and many parts. The designation of NGC 6533 is the whole complex which was first noted by Giovanni Battista Hodierna sometime before 1654. The whole of M8 is comprised of NGC 6523 (northwestern brightest section), NGC 6526 (southeastern dimmer portion) and NGC 6530 (open cluster in the eastern portion). There are also some dark nebulae present that give it an uneven texture. Additionally there are two smaller portions of nebulosity that may or may not be part of the greater complex. IC 1271 is a small bit of nebulosity illuminated by the mag 6.9 star HD 165052 east of the cluster NGC 6530. Another is IC 4678, which is a small halo of nebulosity less than a degree northeast of the center of M8. These last two sections are not typically considered when one things of the larger nebular complex however.
But any way you slice it, M8 is an outstanding visual and imaging treat. Bright and showy at any aperture level, it responds very well to a narrow-band nebula filter, which boosts its contrast significantly. Using an O-III filter is also rewarding. While it dims some of the fainter outer portions, it enhances the darker central regions nicely. If one has both, it is always an interesting comparison to apply each and compare the changes in the view. Even if you’ve seen this object numerous times, it will never disappoint. If you observe from a darker region you are in for a fine display through the eyepiece, and be sure to look for it with the naked eye.
Messier 20 / NGC 6514 (Sagittarius, bright nebula, mag=6.3, size=29.0’x27.0’):
This object is quite unique, as its nickname of “Trifid Nebula” would seem to imply. Noticeably smaller than Messier 8 and a bit dimmer, it still is a beautiful nebula complex, consisting of emission, reflection and dark elements. Discovered by Messier in 1764, he noticed the central star cluster (known to us as OCL-23). William Herschel is the one who noticed “three nebulae” while his son John was the first to utilize the name “Trifid” to describe the nebula. Less than 1.5° NNW of M8, it is easily seen in small apertures within the same field of view. If you have a narrow-band nebula filter in your kit, give it a try to bring out some more contrast.
From darker locations it shows up wonderfully through the eyepiece and is visible with the naked eye just above M8. Also from darker locations, see if you can spot its dimmer reflection portions, predominantly in the northern section of the complex. While it is not quite the showpiece that M8 is visually, M20 is no slouch and presents an interesting visual and imaging target.
NGC 6183 (Ara, bright nebula, mag=, size=20.0’x12.0’):
NGC 6193 (Ara, open cluster, mag=5.2, size=15.0’, class= II3p):
This nice complex is sometimes called the Firebird Nebula and Cluster. Located in northwestern Ara near its border with Norma, the discovery of this field is split between James Dunlop and John Herschel. Dunlop discovered the cluster, later designated as NGC 6193, in 1826 but did not mention any nebulosity in his notations. Herschel formally discovered the nebula in 1836 and also observed the cluster, mentioning both in his discovery notes.
Though the cluster is swaddled in nebulosity, the brightest portions of the nebula lie immediately west of the bright young cluster, which is an OB1 association. Like many such nebular complexes, it consists of both emission and reflective elements, and images also reveal strands of dark obscuring matter traversing the field. This field is a beautiful combination of young hot stars still wrapped in their womb of nebulosity, and one that I’ve had the pleasure of observing a couple of times. I hope you enjoy it as well.
Rest assured the above objects are but a minuscule sampling of the treats available to us during the month of July. The main take away here is to get out there whenever time and weather permit. So let's all get out there and turn our scopes and attention skyward to enjoy the wealth of sights the universe has spread out before us. It is indeed an unlimited buffet for the eyes and the mind.
Astro Sky 17.5 f/4.5 Dob || Apertura AD12 f/5 Dob || Zhumell Z10 f/4.9 Dob
ES AR127 f/6.5 & ED80 f/6 on Twilight-II || Apertura 6" f/5 Newtonian on Twilight-I
TV Ethos 100° 21mm, 13mm || ES 82° 24mm, 18mm || Vixen LVW 65° 22mm
Pentax XW 70° 10mm, 7mm, 5mm || barlows
DGM NPB Filter || Orion Ultra Block, O-III and Sky Glow Filters || Baader HaB Filter
Primary Field Atlases: Interstellarum and Uranometria All-Sky Edition
"Astronomers, we look into the past to see our future." (me)
"Seeing is in some respect an art, which must be learnt." (William Herschel)
"What we know is a drop, what we don't know is an ocean." (Sir Isaac Newton)
"The eternal silence of these infinite spaces frightens me...." (Blaise Pascal)
"No good deed goes unpunished." (various)
"I have become comfortably numb." (Roger Waters)