The Caldwell Objects
Submitted: Monday, 4th December 2006 by Trevor Hand
The Caldwell Objects
by Stephen James O'Meara
The first thing that came to mind when I saw this book was “So who the heck was Caldwell?” We have all heard of Messier and his relentless search for comets, Henry Draper and his stars or Barnard and his dark clouds, but I can’t recall hearing about Caldwell. Shortly after opening the book, the answer became clear. The Caldwell objects were selected by none other than Patrick Moore, Patrick Alfred Caldwell-Moore in the December issue of Sky & Telescope. The penny dropped; obviously to call his list Moore Objects would have produced nothing but confusion, let alone unbelievably painful puns! Unlike the Messier list that was selected largely on the basis of being in the hunting grounds for comets, Moore selected these objects as a representation of some of his favourite celestial treasures. Whilst the Messier list is dominated by objects in the northern hemisphere and lacks objects further south than 34 degrees in Scorpius, the Caldwell objects span the heavens from far north (85 degrees) to the deep south at –80 degrees. Unlike the lack of order in the Messier list; partly due to the method of discovery and partly due to being built up after successive sweeps of the heavens; the Caldwell objects are organised in order of descending declination. This allows an observer to easily determine which objects cannot be seen from their location. At first, I was tempted to read the book starting at the most northerly object visible but decided instead to begin at Caldwell 1 and I recommend you make the same choice. Many of the sections contain interesting information and historical ditties worthy of inclusion in everyone’s pool of useless facts that would be missed if objects not visible by the reader were ignored.
The book begins with a number of notes about how it came to be and his 5-year quest to observe each object. The name O’Meara would be familiar to any regular readers of the American “Sky & Telescope” as he has been a regular contributor for many years and has the fortune of living in what could be described as “astronomical heaven” at a latitude just 20 degrees north of the equator, allowing him to see Polaris, Crux, Eta Carinae and even tempting snippets of the Large Magellanic Cloud as it pops above his horizon. Living at an altitude of 3,600 feet and regularly observing at altitudes in excess of 4,000 feet also allows him to bypass some of the atmospheric effects we all experience; the only drawback being that he lives on the slopes of one of the most active volcanos on the planet, I guess you can’t have everything.
Most of the objects were observed by the author using his rather small Tele Vue Genesis 4 inch scope, of course, under his observing conditions he has the luxury of skies of a clarity many of us could only dream of, however, most objects should be observable with apertures of 200mm in reasonably clear skies at Australian altitudes and conditions, many are observable in much smaller instruments. A number of the more southerly objects were observed during trips to New Zealand. A tremendous amount of research has been invested in this book with contributions from many of his friends and fellow amateur astronomers. Unlike most books, this one does not contain a bibliography but instead has a list of references in one of the earlier sections. A number of mysteries are explained throughout the text including missing clusters, nebulae, galaxies, duplicate and erroneous catalogue entries.
Unlike Messier who began with a bang with M1, The Crab Nebula, Moore begins with a bit of a whimper with an 8th magnitude cluster in Cepheus, NGC 188. The main body of the book is organised into the objects themselves, all 109 of them, the same number as in Messier’s list. Each section contains a simple black and white picture of the object, but not some highly processed image that is not representative of what is seen at the eyepiece, but rather a simple photo to give an idea of what to expect at the scope when observing. A brief history of the discoverer, co-ordinates, magnitude, angular size, constellation, common designation (NGC, IC etc) and comments from Herschel’s viewing logs and other catalogues complete the picture. Every object has a drawing and a finder chart, all oriented with north up. This gives a visual record of each object in every form you could wish for. Some of the more spectacular items also contain black and white images from Hubble to show off further detail. The text contains various descriptions and historical data concerning the discovery or tainted past of some of the items, missing clusters that are noted in some atlases but are nowhere to be found when searched for or have been incorrectly identified by various observers over the years are some of the mysteries explained. Moore chose his objects not because of their splendour or wonder at the eyepiece, but rather because he considered them to be favourites of his and a number of the entries are 10th magnitude or less making them much more challenging than most of the more popular M’s, as a result, star hopping instructions are included for every entry. If there are other interesting objects nearby, the author points these out to expand on the richness of the observing experience. Each entry averages three or four pages allowing a very detailed description while allowing the book to be easily picked up and put down during the odd spare minute or so.
Moore has included many objects that southern observers would include in their own lists and would be the envy of their northern counterparts. The Coal Sack, Eta Carinae, Omega Centauri, 47 Tuc, Tarantula and Jewell Box are just some our local gems. Although the tone of the book is very much “America centric” with many references to how far south an object can be viewed from the United States and numerous references to the world famous Texas Star Party, the author is obviously at least slightly jealous of the south. On his northern pedestal of objects he places Polaris and the security it gave northern explorers by helping to point the way home, whilst in the south he drools over Eta Carinae and the two Magellanic Clouds. Hopefully some of this rubs off onto our northern brethren!
The author rounds out the viewing with 20 of his personal non-Caldwell or Messier objects at the back of the book, his list being evenly spread between northern and southern hemispheres, perhaps to remain “politically correct”. It is interesting that whilst the Messier list contains mainly objects in the north, the Caldwell contains only 51 of the 109 in the north. Three appendices complete the book with a table of each Caldwell object. A discussion of why Messier “missed” the double cluster in Perseus contains an interesting description of the methodology used in his relentless search for elusive comets. The book closes with a very interesting essay about the life and discoveries of William Herschel, arguably one of the greatest astronomical observers the world has ever seen, and possibly ever will.
I found the book extremely interesting and thoroughly recommend it. The text contains many personal observing tips by O’Meara and is written in a very easy, flowing style. Unlike many other astronomical texts, it gives only scant attention to the physics of astronomy and quickly plunges into the “good stuff”. It contains a distillation of many comments and observations by his astronomical predecessors and the results of many hours of research and observation. If you are looking for a modern book to add to your library (published in 2002) you may like to consider this one as many of the “standards” are considerably older (Hartung’s and Burnham’s in particular) and lack some of the touches that this book excels at, finder charts and representative photographs for each object are just a couple of it’s strong points. It is not a wealth of observing targets like its older predecessors, but it is very detailed in the limited number of objects it contains.