The Caldwell Catalogue
A Good Idea Gone Bad - Besides, Several Good Ideas Already Exist
by Alister Ling
It cannot be argued that there is a need and a place for deep-sky references to go beyond the Messier list. The Caldwell Catalogue however, should definitively not be one of those references, for reasons stated farther below.
Most newcomers to deep-sky who have seen a majority of M objects typically fall into one of two classes: 1) Where do I go for more? 2) I need help in going deeper; can you show me?
My favorite references (not an exhaustive list, just the ones I have seen and liked):
Why Patrick Moore's "Beyond Messier: The Caldwell Catalog" is a bad idea
Although it is very laudable of Moore to encourage amateurs to look past the Messiers into the greater - and occasionally more interesting - depths of the night sky, his method is quite inappropriate. If it was simply "Moore's Favourites" or "Moore's Top 100", then fine. What really bugged me was a combination of numerous sloppy errors in the data table and what I personally read as apparent presumptuousness, and apparent self-aggrandisement on Moore's part. I hope it was unintentional.
My disbelief and distaste grew as I continued to read Moore's article. "Caldwell 11, the Bubble Nebula..." Who is ever going to remember the Bubble Nebula as a new number? Who needs to? "The Hyades...appears here as C41." The Hyades sparkle just fine by themselves thank you very much.
Sure, it's a great idea to popularize some lesser-known objects, but did Roger Tory Peterson rename birds in his Field Guides? "The Bald Eagle here appears as Peterson 42..." What would people think of you if you tried that? Where's the promotion here, the objects or him? "Moore, like Messier, begins with`M.' Fortunately, my surname is actually hyphenated - Caldwell-Moore. So let us use C for my catalog."
Moore took most of the favorite non-Messier NGC objects, like the North American, the Eskimo, the Cocoon, the Rosette, the Veil, and rechristened them with C-numbers. Excuse me, did he say "lesser known" ? They've got names, man! Even Hubble's Variable Nebula has been renamed! 31 objects on that list have familiar names. 25 other objects have well-known NGC numbers, like 891, 2419, 4565 or IC entries like 342. You don't see Houston, MacRobert, Webb, or Smyth objects in magazines. William Herschel did not recatalog the Messier list when he published his catalog of deep-sky objects, including 1,000 new discoveries - he left the Messiers with their familiar names. While Moore may be a veteran amateur astronomer and a dynamic television personality, one must wonder how much deep-sky experience he really has. He lists IC 405, the Flaming Star Nebula, as "bright", and at 6th magnitude! Obviously it looks interesting in pictures but he either hasn't seen it or made a double typo with the magnitude and with the associated word.
I'm surprised that Moore (and the editors at Sky & Telescope) perpetuated an historical myth by stating "Yet there are many other objects of equal or greater interest...that Messier did not include, perhaps because there was little chance of confusing them with his beloved comets." The Messier catalogue is not a "could be confused with a comet" list, although non-comets were the driving force behind Messier's compilation. The proper (translated) title is "Catalogue of Nebulae and Star Clusters." Without exception, all open star clusters were resolved and correctly identified as such by Messier. Granted many objects listed by Moore are more interesting than Messier's, but they are definitely not as bright. He seems unaware of the poor optical quality and light grasp of Messier's telescopes: the Great Hercules globular cluster was described as a "nebula without a star." All the northern objects in the C-list (except for the Hyades) are too faint for Messier to have found with his little telescope.
Moore claims to present interesting objects for the observer that are neglected because they are not on the Messier list. Southern hemisphere observers must be shaking their heads in disbelief since magnificent objects like Eta Carinae and Omega Centauri on "his" list make any Messier object pale by comparison. All southern objects in Moore's list would have been easy targets for Messier - alas he did not observe the southern skies at the time. Southerners hardly need to be told by a northerner to seek out "neglected" objects, of which 13 of the 32 (below France's horizon) are visible to the naked eye! After that insult, imagine how they must feel to see both Magellanic Clouds missing from the Caldwell Catalog; the Large Cloud alone contains more interesting stuff in it than all of Cygnus but packed into an area the size of the Scutum starcloud!
The Caldwell Catalog also contains errors too numerous to mention here. A couple of examples will suffice: the very bright Eta Carinae Nebula is given a magnitude of 6.2, while the Tarantula Nebula is listed at first magnitude! The size column, labeled arcminutes (') at the top, actually contains a hodgepodge of object sizes in degrees, arcminutes, or arcseconds. Many of the planetary nebulae have (unexplained in the text) a secondary size on that list, the one measured on long exposure photographs, invisible even to large scope visual observers. I'm at a loss to understand how this shoddiness happens with the current quality and accessibility of measurements in machine readable databases.
The goal of getting observers to look past the Messiers is a good one, but my reception, and perception, of Moore's approach left me reminiscing of a Douglas Adams line from Zaphod Beeblebrox in "A Hitchhiker's Guide to the Universe" : "He's so unhip it's a wonder his buns don't fall off." Thankfully C-numbers will be difficult to memorize - let us bury them deep where the stars do not shine, and promote the already excellent deep-sky references noted at the top of this article.