Region 3
Ophiuchus and Serpens
With 21 globular clusters, Ophiuchus has more for this showdown than any other constellation (one more than Sagittarius). Among those, seven are Messier objects: M9, M10, M12, M14, M19, M62, and M107. The rest are NGC clusters. Of the seven Messier objects, four are in the 6th-magnitude range: M10, M12, M19, and M62. All can be seen without optical aid, and all deserve attention.
M10 and M19 are the dimmest (6.6 and 6.8, respectively) of the four. M10 is only slightly larger (20' compared with 17'), but it’s twice as close, so it is easier to resolve by two magnitudes. So M10 beats out M19 not only on paper, but also through the telescope. Similarly, while M62 shines 0.2 magnitude brighter than M10, its HB magnitude (15.6) does not compare to that of M10 (14.6). Nor do M62’s brightest stars compare to M10’s magnitude 12 suns.
Now let’s compare M10 to M12, which lies roughly at the same distance. M12 is 0.5 magnitude brighter than M10, but M10 is 4' larger. Their HB magnitudes are the same, as is the magnitude of their brightest stars. We need to turn to the telescope to pick a winner.
In my opinion, through an 8-inch scope, M10 wins hands down. Its core is more concentrated and its stars attractively diverse, stretching out in numerous spiral arms. M12 has a softer appearance, which loses out to the visual dynamics possessed by M10.
Now here’s what’s fascinating: M10’s brightest stars shine as brightly as M13’s. Furthermore, M10’s HB magnitude beats out M13’s by 0.3 magnitude. Through the telescope, I enjoy M10’s structure more than M13’s. But alas, the nearly 1-magnitude difference between them keeps M13 at the top.
Of the 14 NGC globular star cluster in Ophiuchus, none is brighter than 8th magnitude, and while six of them are in the 8th-magnitude class, only one has a magnitude (8.3) and HB magnitude (16.2) equal to NGC 6712’s in Scutum: NGC 6293. And although their size difference is only 2', NGC 6293’s brightest stars are a full magnitude fainter than NGC 6712’s. So the visual comparison is undeniably in favor of NGC 6712, which thus far remains on top of the NGC globular clusters in this survey.
Serpens has three globular star clusters: one Messier object (M5) and two NGC objects — NGC 6535 and NGC 6539, which we can immediately discount. M5, however, is a marvel to behold. To compare it to M13, see Showdown 2 below.
As with Omega Cen and 47 Tuc, the clusters have similar visual characteristics. Furthermore, the two lie at similar distances from Earth. So we must turn to our telescope to decide which we prefer. And that’s where we see a difference: M5’s core is more compact (like 47 Tuc’s) and M13 is more open.
I also see more color in M5 (a straw-yellow interior and pale blue exterior) while I detect color only in M13’s diffuse inner region (pale blood red). M5’s core excites me. With a bit of imagination, it seems to be collapsing before my eyes with nervous stellar energy that electrifies my thoughts. Visually, through an 8-inch telescope, M5 gets my vote.
So I replace M13 with M5 as the winner (thus far) in the Messier competition, while NGC 6712 in Scutum remains uncontested in the NGC class. Will they hold on to first place.