The Webb Deep-Sky Society

 

A Visual Atlas of the Magellanic Clouds - written by Jenni Kay FRAS

Introduction

Making visual observations through the telescope of star clusters and emission nebulae in both the Small Magellanic Cloud and Large Magellanic Cloud is an ongoing project of mine. It all began in 1995 while I was using an 8-inch f/10 SCT, an instrument that is generally considered a rather common and small to moderately sized telescope. Late one night in September, after a full night’s observing in Sagittarius, I turned the 8-inch SCT towards the Small Magellanic Cloud, more out of curiosity rather than expecting to see much detail in it. To my surprise I found the SMC to be littered with numerous small hazy glows, all differing in size and brightness, but easy enough to pick out against the bright background glow of the Magellanic Cloud itself.

After sweeping through the SMC with the 8-inch SCT that night, I decided to begin a serious project to observe each and every NGC/IC cluster and nebulae in the SMC. Having slowly and carefully made my way through the SMC successfully, I then turned the same scope towards the LMC. I was astonished! Here, the fields were tightly packed with the glows from numerous clusters and nebulae, much more heavily crowded than what I had found in the SMC. Here was the next challenge, to systematically sweep through the LMC to observe and identify each NGC/IC cluster and nebulae.

The Magellanic Clouds are well placed for making observations in my skies for six months of the year. It took me two seasons, in the years 1995 – 1996, to make my way through both Clouds with the 8-inch SCT. And then I bought a larger telescope, a 12.5-inch f/5 Newtonian on a Dobsonian mount. Of course, this meant I had to review both clouds with the larger scope. This was really a pleasure! 

One of the problems I encountered while working through the Clouds was the misidentification of some NGC/IC objects. Sometimes the modern catalogues had given the NGC or IC designation to the wrong cluster or nebulae, as opposed the one intended by the original astronomer. After noticing that the modern object did not visually match the description as given in Dreyer’s NGC/IC catalogue, it was obvious there was a misidentification here. For example, say the modern object might have appeared very small, and extremely faint, but Dreyer described the object as a very large grouping of bright stars; this conflict in descriptions clearly indicated a misidentification of the object. Once an anomaly like this was noted, I would look up the original astronomer’s descriptive notes. In most cases it was Sir John Herschel who discovered the object and as he logged full descriptive notes on the object the identification problem was quickly sorted out. Using the example above, if Herschel described the object as a large, bright grouping of stars, then the NGC designation did not belong to the very small, extremely faint modern object. In fact, a visual observation through the telescope would show the large bright star group easily enough. 

The common reason for this misidentification stemmed from modern astronomers surveying photo plates instead of to visual telescopic surveys as done by the original astronomers. Usually, the photo plates would reveal a very faint, small cluster at or near the NGC/IC position, where the larger star group was lost, washed out in the deep starry images. In this way, the modern astronomers overlooked the large object and gave the NGC/IC designation to the faint object. It also appears that the modern astronomers, for whatever reason, ignored the original discovery descriptions that would have clearly shown they had the wrong object. Generally, these very faint objects were far too faint for the original astronomer to detect. Therefore, the error occurred here where the modern astronomer gave the name to the wrong object.

Having composed a report on the misidentification on such an object, and offering a correction for it, I posted the report via email to a group of expert people working on similar anomalies in the entire NGC/IC catalogue in general. (More can be found on the work done on this project at the Internet website : http://www.ngcic.com/ngcic.htm.) After further analysis and a brief discussion they confirmed the corrected identification. A chapter on these corrections can be found following the visual observation chapters on the SMC and LMC. 

The following observations were made from my semi-rural home site at Lobethal, SA, Australia. Here, the typical limiting naked eye magnitude is 6.1, with the seeing rated at Antoniadi II-III. The eyepieces used in the 8-inch f/10 SCT were: 
Televue Plossl 32mm @ 66x, and a 46.0' field of view (FOV); 
Televue Wide-Field 19mm @ 110x, and 35.0' FOV; and ...
Televue Wide-Field 15mm @ 140x, and 28.0' FOV. 

The same eyepieces in the 12.5-inch f/5 Newtonian rendered : 
19mm @ 83x, and 47.0’ FOV; 
15mm @ 105x, and 37.0' FOV, and ...
Televue 10.5mm @ 151x, and a 20.0' FOV.

And finally, while I have visual records of observations made through both telescopes, in this work I have decided to include the 8-inch SCT observations on the SMC, the 12.5-inch observations on the LMC, and some selected areas in the LMC with the 8-inch SCT. While this may not “look” very consistent, why include only the 8-inch observations or the 12.5-inch observations? I really found that both instruments could detect nearly all of the same objects. Of course, the 12.5-inch showed them a little brighter, and some were far too faint for the 8-inch. But on the whole, both telescopes did very well offering views of all objects. Getting to my point though, I simply liked the “feeling” captured in my very first set of observations made with the 8-inch SCT through the SMC. And that’s why I chose to include some 8-inch observations over all records made with the 12.5-inch.

Jenni Kay

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