BNGC 20. Eclipsed By the Shadow Of The Mighty

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By Steve Mencinsky, 1995

It would clearly be a gross sin of omission to allow an Autumn to pass without that most fascinating of constellations, Centaurus. So, treating the howls of indignation from the Orionids and their one bright colourful nebula with the disdain that they deserve, we proceed to Uranometria Map 403, where - as we shall discover - for a whole host of reasons Omega Centauri and Centaurus A figure prominently amongst the many items of interest.

As has been previously reported by close friend Lorraine Gall, the two of us spent a most absorbing and productive afternoon in the Mt Stromlo Observatory library, where the films from the 120cm ESO Schmidt yielded a considerable harvest of BNGC objects; intriguingly, many of the in between, around and well within a degree (!) of the afore-mentioned two Centaurians. This article, then, is the first bread from that mill. There are perhaps a few who would regard Omega Centauri as the "best" of the globular clusters by some criterion or other, but surely there would be even fewer who could suggest an easier globular cluster to find. Thus, the large-area chart can be dispensed with; and Chart 1 shows two small and rather faint galaxies, each well within a degree of the nominal centre of Omega.

>From the moderate to-good skies of Lorraine's Wyong backyard, the more southern of the two galaxies was seen almost immediately, using less than 200X. Cigar-shaped, diffuse, yet bright enough to be seen with direct vision through Johannes' 18", the galaxy appeared about the same size as that shown on the Schmidt plates. The more northern one proved to be much more of a challenge: invisible with anything less than the 9mm Naglers 230X, very faint even with averted vision, also cigar-shaped, and considerably smaller than the Schmidt plate suggested. Yet what a find: two galaxies successfully observed, within a degree-and-a-half field around the largest globular! Your correspondent recalls observing them from Ilford under good skies, they looked much the same. Charts 2 and 3 embody both success and disappointment.

The Andrew Murrell Extra-Galactic Library (parse those words as you will!) promised in Klemola 25 "a tightly packed cluster of bright galaxies"; and indeed so it appeared on the Schmidt plate. Disappointment, for not as much as a single one of these could be seen, despite a protracted and intense search at high power. Yet also success, for well away from the main cluster Lorraine spotted on the charts a most promising galaxy, quite dense on the negative; and quite sharp edged.


Indeed, even with the immediately visible, while at high power two different views presented themselves. With direct vision, the galaxy was a mottled jagged arrowhead, while with averted vision an extended outer envelope appeared. The chart attempts to reproduce both of these views.

The last of the Charts, 4 & 5, are of another of Lorraine's finds, encountered en route while cruising the Schmidt film towards NGC 5102. The galaxy's relatively large size and diffuse edges promised not an easy target, and indeed this was what was delivered. An object faint, diffuse, "gradually brighter towards the middle", visible only with averted vision, but quite distinctly visible nonetheless. Almost certainly, from a very dark sky such as Ilford, this could be a most impressive sight. This particular UII chart tempts also with the three fragments of the "other galaxy" with which Centaurus A is reported to have collided, shown in great (computer simulated!) detail at meeting quite some time ago.

Alas, despite the wonderful appearance on the Schmidt films, the search for these was utterly unsuccessful. It was a salutary lesson about the hazards of finding such objects by attempting to plot them from their "central coordinates" (one of the fragments is a good one-third degree long); and of the unrivalled advantage of a suitable photo, despite the well-known limitations of that medium. Your correspondent remains highly sceptical of the reports of those who claim to have seen these fragments through telescopes similar to his. The star patterns near the centre of the fragments - both on the films and as actually observed - are very distinctive. Your correspondent is therefore supremely confident that he was indeed scrutinising exactly the right tiny part of the otherwise anonymous sky. Yet the allegedly successful observers are strangely - and therefore suspiciously - silent upon this point.

On the wall of the office of the Managing Director of AT&T Australia, there are several plaques, each bearing a motivational slogan. One seems very relevant if a trifle multisyllabic: "Luck is what happens when preparation meets opportunity". A most apt description of this month's "lucky" harvest.

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