Welcome to May and hopefully plentiful clear skies for you wherever you live. This time of year the minds of many start thinking of galaxies and in particular the massive Virgo Galaxy Cluster. This delightful piece of celestial real estate is well positioned for most observers no matter if they live north or south of the equator. However, my intent this month is to diverge from that inclination and go in another direction. Instead, we shall focus our attention on my favorite class of deep sky object after my beloved galaxies, globular clusters. Just as spring (north) and autumn (south) signal galaxy season for many, it also signals the beginning of globular cluster season, when many of these interesting objects start to take center stage in the night sky.
This month I have for you not three, not four, but five globular clusters in each celestial hemisphere to pursue. Whether you be a visual only observer or deep sky imaging is your primary focus, the targets will give you ample opportunity exercise your skills. Some are bright showpiece objects, while some may test your skill level a bit as an observer or imager. As with any class of object, sky quality,
aperture and individual skill levels come into play in terms of your success with these targets.
So, let’s dig into this month’s
TSS DSO Challenge. As always, please report back to this forum with your results. If you file reports in the normal Reports forum for visual or the
AP forum for images it is still okay to make posts here for those objects that are part of the
TSS Monthly
DSO Challenge. In that case, duplicate posting is warranted and encouraged when it comes to these specific objects. Just create a new thread within the “Submissions” sub-forum to post your results. Your participation is very much appreciated and I do hope you enjoy the hunt. So let’s get started and see what I have on tap for you in the month of May.
Northern Celestial Hemisphere:
Messier 3 / NGC 5272 (Canes Venatici, globular cluster, mag=6.3, size=18.0’, SBr=12.3, class=6):
Discovered by Charles
Messier in 1764, this beautiful cluster is an annual favorite for observers. You can find it almost half way on a line from Arcturus (Alpha Boötis) to Cor Caroli (Alpha Canum Venaticorum). Bright and large it tickles the senses with its intense core. Its outer fringes resolve fairly easily in mid-sized apertures and with careful scrutiny one can discern lanes that flow outward from the core. Because of its brightness it presents a good imaging target as well, even during nights when the Moon dominates the celestial landscape.
Messier 53 / NGC 5024 (Coma Berenices, globular cluster, mag=7.7, size=13.0, SBr-13.0, class=5):
The ancient constellation
Coma Berenices was named after Queen Berenices of Egypt, wife of King Ptolemy III Euergestes. Though a little dimmer than M3, it is still a fine object for the deep sky observer/imager. It was first located by Johann Bode in 1775 and independently discovered by
Messier in 1777, earning a spot in his list of objects. It can be found just shy of 1° northeast of magnitude 4.3 Alpha Comae Berenices (Diadem), as a somewhat large round globe. A few of its outer halo stars can be resolved in medium apertures, while large apertures may just begin to resolve additional stars at the fringe of the core area.
NGC 5053 (Coma Berenices, globular cluster, mag=9.0, size=10.0’, SBr=13.7, class=11):
Lurking almost 58’ southeast of
Messier 53 and just over 1.5° ENE of Diadem, we now go in search of this challenging object. Discovered in 1784 by William Herschel, who wrote this about the cluster -
"an excessively faint cluster of stars intermixed with resolvable nebulosity 8 or 10' diameter. The stars are so small that they cannot be seen without the greatest attention. 240 verified it beyond all doubts." While there is no nebulosity involved, Sir William was not wrong by calling it excessively faint. Because of its class 1l structure on the Shapley-Sawyer Core Concentration Class scale, its light is very evenly distributed without a strong core. This lowers its surface brightness giving it a ghostly appearance in the eyepiece. With darker skies it becomes easier, but still visually weak overall. It presents as a small and dim rounded glow in smaller to medium apertures, while larger apertures can result in some resolution of member stars. Rest assured this is a challenging object that succumbs easily to the increasing sky glow of more populated areas.
NGC 4147 (Coma Berenices, globular cluster, mag=10.4, size=4.4’, SBr-13.4, class=6):
We remain in
Coma, but move to its western side, just under 3° inside the
Coma-Leo border. This very small globular cluster is a dim little thing and does not yield resolution of member star easily. Larger apertures might just begin to pull out a few of its stars, but doing so is challenging. Officially credited to William Herschel in March 1784, he had observed it a month earlier but his position was off by 20 seconds in R.A. Regardless, his first observation erroneously made it into the record as
NGC 4153. However, use of the entry based on his more accurate second observation,
NGC 4147, is what one will typically find.
NGC 5466 (Bootes, globular cluster, mag=9.0, size=9.2, SBr=13.7, class=12):
We now move into Bootes for our last northern object for this month. Another William Herschel discovery, he swept up this fairly dim cluster in 1784, describing it thusly -
"a large cluster of exceedingly small and compressed stars, about 6 or 7' in dia; a great many of the stars are visible, the rest so small as to appear nebulous; those that are visible are of one size and are scattered all over equally. The cluster is of an irregularly round form." As with
NGC 5053, this one is also very susceptible to sky glow because of its lower surface brightness. Found about 6° southwest of Rho Boötis (mag 3.6) near the border with Canes Venatici, as a class 12 globular it shows no core concentration, thus it presents as a round ghostly glow in the eyepiece. Resolution of some stars at the fringes and possibly across the face of its disk is possible, but the prevailing visual impression will be of a hazy round glow.
Southern Celestial Hemisphere:
NGC 5139 (Centaurus, globular cluster, mag=3.7, size=36.3’, SBr=11.2, class=8
There simply are not enough superlatives to describe the famous Omega Centauri. Of all the globulars I’ve observed, this one is my favorite. Recorded as a star by Ptolemy in 150 AD, it wasn’t until 1677 that Sir Edmund Halley noted its more diffuse nature. Large and showy even in binoculars and small apertures, it is an easy naked eye object for many. Of course city dwellers will likely struggle to see it without optical aid, but it will still be easily found. I have observed it with up to a 5 inch instrument from farther south and it was a stunning beauty, and I described it as an
“explosion of stars.” I recall back in the early 1980s scraping the southern horizon with my then Coulter Odyssey II 17.5 inch in search of this
gem. Of course it was merely a few degrees above the horizon and more of a blobular than a globular.
If you can see it with some elevation, it is a sight you will never forget!
NGC 5286 (Centaurus, globular cluster, mag=7.4, size=11.0’, SBr=12.3, class=5):
Though this cluster shares the same constellation with and lies only a mere 5° southeast of Omega Centauri, it is not observed as much as it should be in my opinion. While it in no way compares visually with
NGC 5139, it is no slouch either. Discovered in 1826 by James Dunlop, it is found only about 4’ northwest of the magnitude 4.6 star HD 119834, sometimes labeled as M Centauri. When I have observed this cluster during trips nearer the equator I never found the star intrusive in terms of seeing the globular and in fact they present a curious and attractive combination. I’ve only observed it with smaller apertures, but always found it bright and quite compact, with a noticeably condensed core. What do you see?
Messier 68 / NGC 4590 (Hydra, globular cluster, mag=7.3, size=11.0’, SBr=12.2, class=10):
Another Charles
Messier discovery, he first spotted it in 1780 and described it as
"a beautiful cluster of stars, extremely rich, and so compressed that most of the stars are blended together.” Found about 3.5° SSE of the Beta Corvi (Kraz), this bright globular show very modest central concentration. Its predominant appearance is of a hazy glow with a few stars being resolved across its disk using medium
aperture. Some mottling may be seen in the core, but it may not resolve appreciably, even at larger apertures.
NGC 4372 (Musca, globular cluster, mag=7.2, size=18.6’, SBr=13.3, class=12):
The celestial fly is home to two globulars. Discovered by James Dunlop in 1826, this large and loosely structured cluster is found in a rich Milky Way field. As a class 12 globular, it shows very little if any core brightness and concentration. In small apertures it may appear as a ghostly orb, but as
aperture increases, resolution of stars becomes possible. It is found about 43.5’ southwest of Gamma Muscae, while a magnitude 6.6 field star is only about 4’ northwest of the cluster and may impact viewing. An interesting aside is a narrow strand of dark nebula, informally known as the Dark Doodad. This curious object runs southwest from the western side of the main figure of Musca, and turns south. Its southern terminus is just northwest and west of the globular. If your sky is dark enough you might notice its presence.
NGC 4833 (Musca, globular cluster, mag=8.4, size=14.0’, SBr=13.9, class=8):
The second cluster in Musca is found off its eastern side, about 42.5’ NNW of Delta Muscae. This cluster was discovered by Nicholas Lacaille in 1751 using his ½ inch 8x refractor at the Cape of Good Hope. He described it in his 1755 catalogue as a nebula that resembled
"a small faint comet." This a bright cluster that will display some internal brightness and one may see some resolution in its outer halo and as
aperture increases this resolution increases against a backdrop of central haziness. You may also notice a mag 8.8 field star at its northern edge.
With that, I hope you will go forth and observe *or image)! Enjoy the hunt and the reward of success. But the main thing here is to have fun, learn and spend time under the night sky. The treasures of the universe are yours to enjoy and ponder every chance you get. Again, good luck and let the rest of us know how you did.