BNGC 12. For A Few Globulars More
By Steve Mencinsky, 1993
A final look at targets galactic for the year as we say farewell to the galactic centre as it slowly wheels overhead and down to the south-west. Without a doubt the most challenging BNGC items in this arena are the non-NGC globular clusters. Although there are to your correspondent's best recollection perhaps three dozen of these, only a handful of these are realistic targets for visual observation in telescopes up to half metre diameters. For example, BNGC of some months ago featured Ton 2, near NGC 6380, which is mentioned here only for the sake of completeness.
Having said that, paradoxically the first on this month's list, HP 1 was successfully observed from Ilford with the late 12" telescope mainly, perhaps, because (a) its plotted position in the very crowded star field in Uranometria II is exactly correct; and (b) its tiny, but [relatively] sharp-edged and hence [relatively] easy appearance.
Palomar 6, again accurately drawn in Uranometria II (and with very good field guide stars nearby), is a complete contrast - in Johannes it is very much larger and much more diffuse.
Palomar 11 is utterly different again. Found exactly in its plotted Uranometria II position, it's relatively large, but with a surprisingly dense, bright and "cometary" nucleus: clearly, it "should" have been an NGC globular.
Andrew Murrell - the Great Globular Hunter - was able to produce several thrilling additional targets, and your correspondent was able to track several of them down. As they are not shown in Uranometria II, they are drawn here.
On chart 429 (left), very close to Gamma Centauri is the globular cluster Ruprecht 106. As can be seen from the CHART, this cluster is almost "on top of" an 8th magnitude star. In Johannes, the glare from this star is such that there is no question of determining its exact shape, even though spotting the cluster itself was quite easy.
Chart 451 (below) shows, in between the Coal Sack and the spectacular bipolar planetary nebula NGC 5189, another faint globular: Arp-Longmuir 1, aka AL 1, aka ESO-96-SC4. This cluster was quite easy to find, quite large, very diffuse and surprisingly spherically symmetrical, which seems fairly rare for these very faint clusters.
Finally, the greatest delight of all. Found without a chart, merely from Andrew's terse "From Barnard 86, go the opposite direction to the open cluster [NGC 6520] and about twice the distance (as the open cluster), immediately before another small dark nebula", is another small, round, faint and diffuse cluster: DJ 2. This globular was quite easy to see from the recent Queensland AstroFest, where we also had the opportunity of seeing a colour photo of this area taken (with a C8) by new friend Brendon Downs, in which DJ 2 appears very reddish-brown. This is perhaps consistent with the comment in Burnham's, which describes the 7 hour (!) exposures taken in a search for the very centre of the galaxy (VCG); these revealed "extremely reddened globular clusters". Incidentally, the photo of Barnard 86 in Burnham's shows but does not identify DJ 2: if you wish to confirm this yourself, the drawing below may prove a useful guide. On the drawing the dark nebulae are outlined as to their visual appearance; these may not necessarily coincide with the photographic outlines of said nebulae. Also, the stars shown with crosses are those that appear red or orange: this close to the VCG, the proportion of these is quite high.
As this area is so close to the VCG ( G 4 degrees), it is truly an observational smorgasbord. In the one wide-angle field, there is Barnard 86, NGC6520, the nearby bright orange star, the faint globular, the entire eyepiece field strewn with stars and marbled with small diffuse bright and dark nebulae - indeed a truly wonderful sight!
Andrew has claimed success with another half-dozen faint globular clusters of an allegedly similar degree of difficulty, but your correspondent with his rapidly ageing eyesight has been unable to see any of these in Johannes. Perhaps if the Giant Ilford Telescope ever becomes reality some of these could become observational triumphs for many of us?