by Jim King
Why did Charlie chase comets???
Given the incredible and efficient technologies used to discover comets in the twenty-first century, both on Earth and in space, many of today’s telescopic observers pursue comets mostly as objects of passing interest—especially when they blaze forth to naked-eye splendor or threaten to hit the earth…or other planets. Note, however that owing to the same leaps in technology, some amateur astronomers across the globe also conduct extremely serious studies of, and searches for comets, and have contributed greatly to the science. Nevertheless, to the mid-eighteenth-century observer, comets were among the most mystifying sights in the sky. The astonishing appearance of six-tailed C/1743 XI (Cheseaux’s comet of 1744) – one of the greatest since the dawn of modern astronomy – may have inspired Messier’s lifelong passion for comets.
With history having recorded only some 50 comets know by Messier’s time, these celestial itinerants presented the burgeoning telescopic astronomers of the day not only with a fascinating challenge (namely to find them) but also the promise of some fame and notoriety.
Messier was the man who first thrust this challenge to the forefront of astronomical desire.
(An important jargon jogger: Messier uses the descriptive term “nebula” 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.)
M4 Globular Cluster (Observability: Apparent*) Riding high in the summer sky, globular cluster M4 awaits the inquisitive gaze of amateur astronomers using the smallest of apertures – including the unaided eye. Swiss astronomer Philippe Loys de Cheseaux (1718-1751) discovered the glow “Close to Antares” in 1746, describing it as “white and round”.
When you probe the depths of this cluster, keep in mind that you are looking at an object about 75 light years in diameter and roughly 13 billion years old, a senior member of our Milky Way galaxy, which formed in the early stage of the Galaxy’s evolution, during the collapse of the protogalactic cloud. We see it receding from us at 44 miles per second.
Messier note: Observed May 8th, 1764. “Cluster of very faint stars. With a small telescope, it looks like a nebula. This star cluster is close to Antares and the same parallel. “
NGC note: “Cluster, with 8 or 10 bright stars in a line with 5 stars, well-resolved.”
Data: Messier4 aka NGC 6121
Con: Scorpius Mag: 5.4
RA: 16h23.6m Dec: - 26.31.5
Dist: ~7,200 light years
M14 Globular Cluster (Observability: Apparent *) For the same reason M13 is described as a magnificent piece of eye candy, and thus very popular, M14 is considered to be rather sucky. It is beyond the normal naked-eye limit and lies in a region of sky belonging to an obscure part of Ophiuchus in the Serpent Bearer’s left arm. Yet, it can be detected through binoculars. Telescopically, M14 is surprisingly detailed and deserves special attention.
M14 is a somewhat metal-rich cluster 33,300 light-years from us and only 13,000 light-years from the Galactic center, near the dark folds of the northern extremity of the Galactic bulge. The giant mass spans 106 light-years of space and is receding from us at 41 miles per second.
Messier note: Observed June 1, 1764 “Nebula without a star, discovered in the drapery that hangs from the right arm of Ophiuchus. This nebula is not large, and its luminosity is feeble; however, it may be seen with a simple three-and-a-half-foot refractor; it is circular.”
NGC note: “Remarkable globular cluster, bright, very large, round, extremely rich, very gradually much brighter in the middle, well-resolved, 15th-magnitude stars and fainter.”
Data: Messier14 aka 6402
Con: Ophiuchus Mag 7.6
RA: 17h37.6m Dec: -3.14
M19 Globular Cluster (Observability: Apparent ) * Despite what the NGC’s description says, M19 in Ophiuchus is a challenging object to resolve. Although the cluster shines with a total magnitude of 6.8, the average brightness of its most luminous stars is about magnitude 14.
MJ19 is the most elongated globular cluster known. The reason for this great degree of ellipticity appears to be the cluster’s extreme proximity to the Galactic center (only ~5,500 light-years from it) and only 9 degrees from the Galactic plane. We see it approaching us at about 85 miles per second.
Messier notes: Observed June 5th, 1764 “Nebula without stars, on the same parallel as Antares, between Scorpius and the right foot of Ophiuchus. This nebula is circular; it is clearly visible with a simple three-and- a half-foot refractor.”
NGC note: “Globular, very bright, large, round, very compressed in the middle, well-resolved. It consists of stars of the 16th-magnitude and fainter.”
Data: Messier 19 aka NGC 6273
Con: Ophiuchus Mag 6.8
RA: 17h02.6m Dec: -26.16
Dist.: ~28,700 ly
M55 Globular Cluster (Observability: Apparent) * One of the most southerly globulars observed by Messier, M55 was included in a study of globular cluster motion that revealed that these stellar assemblies are moving at high speeds (greater than 100 miles per second) in elliptical orbits through the distant halo of our Galaxy somewhat like long-period comets in orbit around the Sun. At a distance of only 17,300 light-years, however, M55 is relatively nearby. One can see it with the naked eye on the outskirts of the Milky Way band.
In 7 x 35 binoculars, M55 looks like a hairy star. With a 4-inch at 23x, the cluster starts to splinter across its large and loose surface – a refreshing sight after looking at the smaller, more difficult globulars M54, M69, and M70 nearby. In fact, M55’s disk looks huge when compared with the disks of those globulars, even on high power.
Messier note: Observed July 24th, 1778 “Nebula that appears as a whitish patch, about 6 minutes across. Its light is evenly distributed and has not been found to contain any star.”
NGC note: “Globular, very bright, large round, very rich, very gradually brighter in the middle, stars from 12th magnitude to 15th magnitude.”
Data: Messier 55 aka NGC 6809
Con: Sagittarius Mag 6.3
RA: 19h40.0m Dec: -30.58
Dist.: ~17,600 ly
* Sky Tools software offers an observability scale of 1 – 6, with 1: Obvious; 2: Easy; 3: Apparent; 4: Difficult; 5: Challenging; and 6: Very Challenging. The 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!
Want more? Check out the HAS website under “Programs”/Messier Challenge/HAS 45