By Jim King
Over the past year, we have delved into some of the most spectacular objects in the night sky for specific timeframes that brother Messier had to offer. Due to limited space on these pages, there have been some unfortunately necessary stragglers remaining from each season. I will, in the next few months, finish up Messier, hopefully bringing them to your attention in a season when one can still find them with reasonable effort.
I also tried to occasionally bring to the forefront some interesting facts about the man and the times. Messier was a truly remarkable man with significant challenges. I would encourage you who are interested, to do a little research on your own. I can think of no better place to start than by obtaining a copy of Stephen James O’Meara’s Dark Sky Companions / The Messier Objects.
(An important jargon jogger: Messier uses the descriptive term “nebula” frequently since he was frequently using a 3.5 inch telescope which had difficulty resolving dim stars. It appears that he thought “nebulae” were not gas clouds, but simply unresolved star clouds. Therefore, in our descriptions, we must mentally separate Messier’s “nebulae” from the real thing. He does differentiate nebulosity from luminosity.)
M 6 Open cluster (2 easy) *
Arguably observed throughout history as a naked-eye nebulous star.
Messier note: (Observed May 23, 1764) Cluster of faint stars between the bow of Sagittarius and the tail of Scorpius. To the naked eye this cluster appears to form a starless nebula, but even the smallest instrument will show it to be a cluster of faint stars.
NGC note: Cluster, large, irregularly round, little compressed, one star of magnitude 7, and then stars 10th magnitude and fainter.
Data: Messier 6 aka NGC 6405 aka Butterfly Cluster
Con: Scorpius Mag: 4.2
RA: 17h40.3m Dec: -32.15.5
M 7 Open cluster (3 detectible) *
Located about 5 degrees north-northeast of the blue subgiant star Lambda Scorpii, the easternmost of the Scorpion’s two stinger stars, open star clusters M6 and M7are two of the most striking details projected against the hub of our galaxy – a dramatic naked-eye oval expanse of milky starlight and dark dust. These clusters are among the more brilliant Messier objects in the night sky. M7, the southernmost Messier object, is arguably the brightest spot in the entire visual Milky Way. M6 and M7 all but dominate the summer Milky Way and erupt like distant fireworks. Both clusters are visible to the naked eye as puffs of “smoke” even under full Moonlight.
Messier notes: (Observed May 23, 1764) A larger cluster of stars than M6. This cluster appears to be a nebula to the naked eye; it is not far from M6, lying between the bow of Sagittarius and the tail of Scorpius.
NGC notes: Cluster, very bright, pretty rich, little compressed, stars of 7th to 12th magnitude.
Data: Messier 7 aka NGC 6475
Con: Scorpius Mag 3.3
RA: 17h53.8m Dec: -34.47.1
Dist.: ~780 Ly
Discovered by Claudius Ptolemy, second century A.D.
M 9 Globular cluster (5 challenging) *
As you hunt down the Messier objects, try to forget any preconceived notions you might have about their appearance. For example, it is easy to assume that all Messier globular clusters will at first appear as tight, fuzzy balls of starlight. But M9 is clearly an exception. It immediately looks different, as though someone has tried to erase it from the sky. It is amazing that Charlie found the nearly 8th-magnitude glow with his inferior instrument in 1764.
Messier notes: (Observed May 28th, 1764) Nebula without a star, in the right foot of Ophiuchus; it is circular and its light faint.
NGC note: Globular cluster, bright, large, round, extremely compressed in the middle, well resolved, stars of 14th magnitude.
Data: Messier 9 aka NGC 6333
Con: Ophiuchus Mag: 7.8
RA: 17h19.2m Dec: -18.31
M 10 Globular Cluster (3 detectible) *
M 10 is a bright and beautiful globular cluster in Ophiuchus, nearly equidistant from us and the Galactic center. It makes a nice pairing with globular cluster M 12 just 3 degrees to the northwest. Charles Messier discovered these clusters on successive nights in May 1764. William Herschel resolved M 10 in 1784, noting a very compressed core of stars, which is interesting because, while the core is bright, it is not very compact.
Messier notes: (Observed May 29, 1764) Nebula without a star, in the belt of Ophiuchus, close to the thirtieth star in this constellation, which is of magnitude 6, according to Flamsteed. This is a beautiful, circular nebula; it can be seen only with difficulty with a simple three-foot refractor.
NGC note: Remarkable globular, bright, very large, round, gradually very much brighter in the middle, well resolved. Stars of 10th to 15th magnitude.
Data: Messier 10 aka NGC 6254
Con: Ophiuchus Mag: 6.6
RA: 16h57.1m Dec: -4.06
Dist: ~14,350 ly
M 12 Globular Cluster (3 detectible) *
The enormous summer constellation Ophiuchus harbors nearly two dozen globular clusters within range of small telescopes, and seven of them were catalogued by Messier. Small, but spectacular, M 12 lies only 3.5 degrees northwest of M 10 (a nearly identical globular). Use binoculars, or your telescope on low power to view the clusters together for a twin treat. Separated by only 3,700 light-years, these two star-packed clusters are virtually cosmic neighbors.
Messier notes: (Observed May 30, 1764) Nebula discovered in Serpens between the arm and the left side of Ophiuchus. This nebula does not contain any stars, it is circular, and its light is faint.
NGC note: Very remarkable globular cluster, very bright, very large, irregularly round; gradually much brighter in the middle, well resolved, stars of 10th magnitude and fainter.
Data: Messier 12 aka Gumball Globular aka NGC 6218
Con: Ophiuchus Mag: 6.1
RA: 16h47.2m Dec: -1.57
Dist ~15,650 ly
* Sky Tools offers an observability scale of 1 – 6, with 1 being “Obvious” and 6 being “Very Challenging”. The particular rating scale I use is based on a Celestron SCT 8 Evolution telescope at the HAS dark site on a moonless night.
Ex astris, scientia, y’all!
Field Trips and Observing Chair
Want more? Check out the HAS website under “Programs”/Messier Challenge/HAS 45