Messier Column - October 2021

Original article appears in GuideStar October, 2021.

by Jim King

We have evidence that Messier may have been in poor physical condition during his later life. In 1802, Herschel visited the 72 year-old Messier in Paris, writing in his diary that Messier had “complained of having suffered much from his accident of falling into an ice cellar – an accident that had occurred two decades earlier.  Messier had also lost his wife and suffered from failing eyesight.  Although he continued to make the occasional observations, the climb up the octagonal tower to his telescopes must have also become arduous to his weary bones, especially on cold, damp nights.

 

(I can relate)

***

(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.)

M2 Globular Cluster (2 easy) *

In the fall, the vast summer Milky Way slips slowly into the western horizon after sundown.  Hours will pass before mighty Orion and other bright winter constellations rise in the east.  Looking overhead, we now peer straight out of the galaxy – away from the crowded stellar cities of the Milky Way’s arms into the suburb of stars whose residents include some of the most inconspicuous constellations in the night sky; chief among them Aquarius, the Water Bearer.  It is largely indefinable, and its faint stars must compete with light pollution.  Nevertheless, Aquarius contains a secret treasure well worth hunting for   - the spectacular globular cluster M2. 

Jean-Domonique Maraldi (1709-1788) first spied this “nebulous star” from Paris on September 11, 1746, while searching for Cheseaux’s comet.  Maraldi called it “very singular” in that he could not resolve any star within it, nor within the entire telescopic field.

Messier independently chanced upon this object on September 11, 1760.  M2 is certainly a marvel.  This 175-light-year-wide swarm of 150,000 stars is replete with yellow and red giant stars about 13 billion years old.

Messier note: (Observed September 11, 1760) Nebula without a star in the head of Aquarius.  The center is bright, surround by circular luminosity; it resembles the beautiful nebula that lies between the bow and the head of Sagittarius. 

NGC note: Very remarkable globular cluster, bright, very large, gradually much brighter toward the middle, well resolved into extremely faint stars.

Data:     Messier 2 aka NGC 7089

                           Con: Aquarius                                             Mag: 6.5

                            RA: 21h33.5m                                             Dec: -00.49

                            Dist: 37,500 ly

M15 Globular Cluster (2 easy) *

Nearly the twin of M2 in Aquarius, this glittering gem in the winged horse Pegasus is one of six beautiful globular star clusters brighter than 7th magnitude that grace the northern sky.  The great Pegasus Cluster, M15, can be spotted without difficulty as a “fuzzy star” with the unaided eye, lying just 4 degrees northwest of the of the topaz 2nd magnitude star Epsilon Pegasi.

Messier notes: (Observed June 3, 1764) Nebula without a star between the head of Pegasus and that of Equuleus.  It is circular and the center is bright.

NGC notes:  Remarkable, globular cluster, very bright, very large, irregularly round, very suddenly much brighter in the middle, well resolved into very faint stars.

Data:     Messier 15 aka Great Pegasus Cluster aka NGC 7078

                           Con: Pegasus                                               Mag 6.3

                           RA: 21h30.0m                                             Dec: +12.10

                           Dist.: ~33,900 ly

M30 Globular Cluster (2 easy) *

M30 is a fairly large globular cluster with a few hundred thousand stars splashed across 90 light-years of space.  We see it whizzing away from us at 115 miles per second.  M30 is one of the Galaxy’s most extremely metal-poor globular star clusters, with each of its members, on average, containing about 1/186 as much metal per unit of hydrogen as the Sun.  The cluster has an integrated spectral type of F3 and an estimated age of 13 billion years. 

Shining at magnitude 6.9, the moderately condense glow is surprisingly obvious under a dark sky through 10 x 50 binoculars.  Visually compressed, M30 has a tiny core inside a 12’ globular haze, though only about half that size appears dominant through the telescope.  Despite the object’s brightness, low power does not resolve it at all.    

Messier notes: (Observed August 3, 1764) Nebula discovered below the tail of Capricornus, close to the sixth magnitude star Flamsteed 41.  It is difficult to see with a simple 3.5 foot refractor.  It is circular and does not include any stars.

NGC note: Remarkable, globular cluster, bright, large, little extended, gradually, pretty much brighter in the middle, stars from 12th to 16th magnitude.

Data:     Messier 30 aka NGC 7099

                           Con: Capricornus                                        Mag: 6.9

                           RA: 21h40.4m                                              Dec: -23.11

                           Dist: ~26,400ly

M72 Globular Cluster (3 detectible) *

M72 is Messier’s faintest globular.  At magnitude 9.2 and just 6’ in apparent diameter, this globular is easy to pass over.  Look for a 9th magnitude “double star” separated by 5’ – the eastern component is, in fact a star; the western component is M72.  Once found, use moderate magnification to enlarge the cluster’s disk.

One of the reasons M72 appears so feeble is its distance; the cluster lies about 55,000 light-years from the Sun and 42,000 light-years from the galactic center.  Yet, in true physical extent, it spreads across about 110 light-years of space.

Messier notes: (Observed October 4, 1780, sort of) Messier was unable to clearly identify this object.  His assistant M. Mechain spotted it on the night of August 29, 1780. 

NGC note: Globular, pretty bright and large, round, much compressed in the middle, well resolved.

Data:     Messier 72 aka NGC 6981

                           Con: Aquarius                                             Mag: 9.2

                           RA: 20h53.5m                                              Dec: -12.32

                           Dist: ~55,400 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.

Finito!

Ex astris, scientia, y’all!

Jim King

Field Trips and Observing Chair

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