December’s column will finish up the Messier fall/early winter group. This is a case of last, but not least. All of Messier’s objects are worth the effort to locate and spend some time wallowing in their beauty.
(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.)
M 56 Globular cluster (3 detectable) *
M56 is a relatively rich but metal-poor globular cluster in the halo of our Galaxy – nearly the same distance from us as it is from the Galactic center (~30,000ly). It is receding from us at about 85 miles per second. With 1/95th of it composed of metals, it is not only one of the most metal-poor globulars known but also one of the oldest (~ 13 billion years) in the galactic halo.
In a low-power view, a faint stream of stars flows from the southeast and drains into M56’s foggy pool. The tiny round glow (actually ~62 light years across) is punctuated by a 10th magnitude star to its west. Moderate power starts to resolve the cluster, which immediately appears elongated north to south. In fact, the inner core is highly asymmetrical. With a thin fan of material to the south and nothing like it immediately opposite to the north, the innermost region of M56 is quite unique, looking like a light bulb or an exclamation mark.
Messier note: (Observed January 23, 1779) Nebula without a star, which is very faint. Messier discovered it on the same day as he discovered the comet of 1779.
NGC note: Globular cluster, bright, large, irregularly round, gradually very much compressed in the middle, well-resolved, stars of 11th and 14th magnitude.
Data: Messier 56 aka NGC 6779
Con: Lyra Mag: 8.3
RA: 19h16.6m Dec: +30.11
Dist: ~30,600ly
M 73 Asterism (3 detectable) *
A Y-shaped asterism conveniently situated 1.5 degrees east of M72, M73 is a grouping of four stars – specifically GSC (General Star Catalogue) numbers 05778-00802, -00492, -00509, and -00594 – with no apparent connection except that they lie in the same line of sight.
Not of any great import, other than that they are kinda cool to look at.
Messier notes: (October 4th and 5th, 1780) Cluster of three or four faint stars, which at first glance, resemble a nebula, and does contain some faint nebulosity.
NGC notes: Cluster, extremely poor, very little compressed, no nebulosity
Data: Messier 73 aka NGC 6994
Con: Aquarius Mag 9.7
RA: 20h58.9m Dec: -12.38
Dist.: unknown
M 77 Spiral Galaxy (2 easy) *
M77 is a prototype of a peculiar class of extragalactic objects known as Seyfert galaxies. These systems have very active nuclei which are potent emitters of radio-wavelength energy and whose spectra show strong emission lines – characteristics also displayed by the distant quasi-stellar objects, or quasars. But quasars are infant systems billions of light-years distant, whereas energetic M77 is a mere 44 million light-years distant.
Apparently, gas clouds (some with a mass 10 million times the Sun’s) are blasting away from the nucleus of M77 with velocities up to 360 miles per second and enough energy to power several million supernova explosions!
M77 is the closest you will ever come to seeing a quasar in action.
Messier notes: (Observed December 17th, 1780) Cluster of faint stars which contain nebulosity.
NGC note: Very bright, pretty large, irregularly round, suddenly brighter in the middle, some stars seen near the nucleus.
***
* Sky Tools offers an observability scale of 1 – 6, with 1 being “Obvious” and 6 being “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.
Finito!
Ex astris, scientia, y’all!
Jim King
Field Trips and Observing Chair
Want more? Check out the HAS website under “Programs”/Messier Challenge/HAS 45
