Comparing Caldwell’s globs
Like with the Messier catalog, there’s a wide variety of globular structure in the Caldwell objects too. Not one single cluster looks the same! That is if you are prepared to spend time on the target and give it the attention that it deserves. Unfortunately the Caldwell globs are not evenly distributed in the sky. If you are located in the northern hemisphere (like me) then you will notice that only 3 objects can be seen with ease. For all other 15 (!) you will need to go south. In my case I observed a couple more from La Palma, but for a true spectacle you will need to head as much south as you can. It is still on my to do list for the years to come…
NGC 2419 is the most northern one in the list and it’s the one at the largest distance from us. It’s for a reason that it’s called the “intergalactic wanderer”. At about 300.000 light years away, nothing more can be seen than a round nebulous object. I could resolve no stars in it, although some dim stars can be seen in the direct vicinity, as well as three bright stars that seem to point directly to it. Sketched with the 10″ Alkaid @171x.
Two more of the northern Caldwell globular clusters are located near each other in Delphinus and appear very different from each other. I sketched both within the timeframe of a month.
NGC 6934 is a nice glob that does not appear very concentrated. The core is not much brighter and with AV some stars can be resolved. A large halo of graininess can be seen, almost up till the brightest star in the field. The shape is certainly not round; on the right side three extensions are visible, making the cluster appear like a shuriken. Sketched with the 16″ Alkaid @259x.
NGC 7006 is very small and condensed and does not immediately appear as a globular cluster. At first glance it looks more like a galaxy and only when increasing the magnification the grainy texture becomes somewhat apparent. The shape is perfectly round and the 2/3 center is pretty much evenly illuminated. With AV a 1/3 glow is visible around it. Sketched with the 16″ Alkaid @362x
On La Palma I have observed many globular clusters and part of those can be found in the Caldwell list. In 2019 I aimed the 10″ Alkaid at two objects that differ a lot in size. Both were sketched with the 5mm at 240x.
NGC 5694 is a very small and dim cluster in Hydra. The core has a droplet shape and is only a bit brighter. The core area is relatively large and the graininess can barely be seen. Therefore it’s not very imposing.
NGC 3201 on the other hand is huge! The rhomboid shape shows a loose structure, only a bit more concentrated towards the core. Some nice star chains run away from it, but one is cutting straight through. On closer inspection, some dark spots are visible on the foreground and at least three of them can be held long enough to draw them with confidence. Even this far south, the glob hangs low in the sky and the light travelling through the atmosphere is smothered to some degree, which has its effect on the resolvability. I can imagine that when this one would be observed in zenith it must be quite a showpiece.
NGC 1851, number 73 on Caldwell’s list, is a fairly large and round globular cluster in Columba with a dense and bright (unresolvable) core. In the halo, most stars can be resolved, especially a “V” of somewhat brighter ones around the core. A darker lane is visible directly under the core and the graininess on the left side of the GC lights up just a bit more than in other areas. A beautiful object, even at a culmination of only 21 degrees here at La Palma. Sketched wth the 10″ Alkaid @ 171x.