BNGC 6. The Jewel On The Cloud
By Steve Mencinsky, 1993
How many objects worthy of observation are there in the Large Magellanic Cloud (LMC)? A glance at the cover of Uranometria reveals hundreds. OK, how many of these are non-NGC and hence worthy of consideration for this column? A comprehensive search of the same cover reveals only one, the subject of this month's BNGC: the bubble nebula Henize 70 (N070). Uranometria also lists its internal stellar association from the Lucke-Hodge catalogue: LH120.
This object seems to have been very harshly treated, seemingly being judged unsuitable for observation in amateur instruments. Anton Becvar in his "Skalnate Pleso" lists it as a planetary nebula, which is in complete discordance with modem thinking. Amazingly, Mati Morel's beautifully detailed charts ignore it completely. It's not that faint: on a recent weekend at Ilford the shape was clearly seen in the 18" telescope / OIII filter combination through cloud thick enough to reduce the naked-eye limit to about second magnitude!
With many of the smaller and/or fainter objects in the LMC, the difficulty is not in finding said objects, it is in the identification: "Let's see, this bright blob must be NGC 1850. So that small and faint blob must be HS109 (Hodge-Sexton). In that case, what's that even fainter one further out? Is that SL260 (Shapley-Lindsay) or HS122?" Fortunately, N070 is large (about 8' in diameter), its position is easy to define, precisely (1.3 degrees NNW position angle 330 from the centre of the Tarantula), and finally it's in an area of the LMC that is sufficiently free from distracting nebulae (relatively speaking). It is therefore easy to locate and, equally as important, easy to identify positively.
When observing this object, the LH120 stellar association is the first thing that leaps to the eye's attention, like a micro-miniature M18. After only a few seconds, one becomes aware of the almost perfectly spherical surrounding glow of N070. The OIII filter confirms it without a doubt. On a recent trip with Andrew Murrell to the very, very dark skies of Coonabarabran, N070 showed some Very superb detail in the 50 cm / OIII filter. The most memorable of these were the bright and thin double strands of the north rim; the very diffuse, wide and braided southern segment; the scalloping along the western and eastern edges; and the area of the central LH120 association.
The chart above, left shows the key objects and stars that are conspicuous on the short and very pleasant stroll from the Tarantula nebula to N070. Please note that unlike most charts, this one is drawn with North to the right. A parting shot: anyone who suspects that The author made up the cluster names as he went along is invited to borrow the Society's copy of Mati Morel's charts and associated booklet and to observe these objects for him/her self.