 |
Book Review - Deep-Sky Companions: The Caldwell Objects |
Posted by Michael Cohen, Mar 22, 2004
Deep-Sky Companions: The Caldwell Objects with a foreword by Patrick Moore. Stephen James O'Meara (Sky & Telescope and Cambridge University Press, 2002) 484 pages. 0-933346-97-2. $39.95
In Deep-Sky Companions: The Caldwell Objects , Stephen James O'Meara does his best to preserve a badly-kept secret about Patrick Moore's list of deep-sky objects: most of them are not really small-scope targets. Oh, true enough, some of them don't even need a telescope of any size: the Hyades in Taurus (Caldwell 41) and the Double Cluster in Perseus (Caldwell 14) are beautiful naked-eye objects, even more spectacular in binoculars, and the same may be said of the southern-sky objects Omega Centauri (Caldwell 80), the Eta Carinae Nebula (Caldwell 92), and the Southern Pleiades (IC 2602, Caldwell 102). Equally true, some of the Caldwell objects are spectacular in small scopes, especially rich-field ones. The North America Nebula (Caldwell 20), the Sculptor Galaxy (NGC 253, Caldwell 65), the planetary nebula known as the Ghost of Jupiter (Caldwell 59) and the Helix Nebula (Caldwell 63) all reward observation with telescopes of any size. Since Patrick Moore specifies here, in a preface especially written for this volume, that all the objects on his list should be observable by amateurs using 4-inch or larger telescopes under dark skies, we should hold him to his word, though we should not ignore his additional comment that some of these objects should be more difficult than others, and that an observer should be challenged by the list.
Stephen O'Meara is up to the challenge, and the result is a book even better in many ways than his earlier one on the Messier objects, now a modern classic. But the lesser mortals among us need to pause before we assume our experience with the Caldwell objects will be his. O'Meara does indeed use a 4-inch telescope. But his telescope is a Tele Vue Genesis refractor combined with Nagler eyepieces, his observations are from clear skies at 4,200 feet on the big island of Hawaii, and his eyes are those of the premier visual observer of our time, the man who saw the latest return of Halley's comet before anyone else, and who identified spokes on Saturn's rings that Voyager photos confirmed before any other earthbound observer could see them. Of his equipment and situation, O'Meara says that his 4-inch Genesis under his observing conditions will show the same detail that a suburban observer can see in an 8-inch Schmidt-Cassegrain. If O'Meara has difficulty seeing any objects from the Caldwell list, in other words, the rest of us might reasonably expect to have difficulty seeing them also with anything less than an 8-inch scope. And he does have difficulty with some of these objects. NGC 3626 (Caldwell 40), he writes, is "only marginally visible in small telescopes," and he wonders why Moore didn't choose another lenticular galaxy in Leo, 1° away and a full magnitude brighter, for Caldwell 40. Through his 4-inch scope, O'Meara sees NGC 1275 (Caldwell 24) as "less a firefly and more a piece of starlit lint." Of NGC 7635, the Bubble Nebula (Caldwell 11), O'Meara says "Unfortunately the Bubble is not a feature to be glimpsed casually through small telescopes . . . it takes large apertures." The Cave Nebula, Sharpless 2-155, which is the 9th object on Moore's list, O'Meara calls "a near impossibility" through the Genesis 4-inch, "even when viewed at an altitude of 4,200 feet under transparent Hawaiian skies." These reservations should not deter anyone from attempting the Caldwell list, especially with an instrument of 8 inches or more. And it may well be that the modern definition of "small scope" has changed so that amateurs now consider an 8-inch well within its range.
In any case, if you have the urge to challenge the Caldwell objects, you will not find a better guide than Stephen O'Meara, or a better thought-out guidebook than this one. A typical entry for one of the objects may be as short as a single page of text (500 words) or as lengthy as the satisfying 2500-word essay devoted to the Hyades. Each entry has coordinates, magnitudes, dimensions, and distances. O'Meara takes note of the object's discoverer and date, and he provides descriptive comments by William Herschel if they are available. He also reprints comments from the 1864 General Catalogue of Nebulae (noting that where its observations do not match William Herschel's they are probably John Herschel's) and Dreyer's 1888 New General Catalogue. The photos are well chosen, and in some cases, have been shot to order for the book. Many come from the Digitized Sky Survey, both Northern and Southern Hemisphere, and more than half were made by a small group of astrophotographers: Akira Fujii, Preston Scott Justis, Martin Germano, Luke Dodd, Kim Zussman, and Sean Walker. One superb photo of the Rosette Nebula may be recognized as Hans Vehrenberg's. All the photos are in black and white, because O'Meara does not wish to give amateur observers the impression they will see more in the eyepiece than is possible. As always, O'Meara's drawings are painstaking, surprising in their detail, and clearly the product of long sessions of patient watching. Pains have been taken to make the book as observer-friendly as possible, and O'Meara has learned from a few features in Deep-Sky Companions: The Messier Objects that were irritating. Thus, for example, the finder charts (by Roger Sinnott), the photos, and O'Meara's drawings are all oriented with north upward in this book, and the photos and drawings usually have comparable scales. Careful star-hopping directions take us to the objects, often from several possible directions. NASA and the Hubble Heritage Team photos provide a few striking images when O'Meara wants to discuss interesting or recently-discovered features in the objects. Thus there are Hubble close-ups of the cometlike knots or globules in the Helix Nebula as well as of the ring of starburst clusters around the nucleus of the Sculptor Galaxy. O'Meara even goes so far, in the entry on the Hyades, to include a Magic Eye illustrationa stereoscopic image so that we can look at the cluster in three dimensions. For Hubble's Variable Nebula (Caldwell 46), he not only provides a solid, five-page essay, but also sequential photos to show the variability. O'Meara discusses all of the objects with an engaging style that makes us share his interest.
Because most observers will be more familiar with common names, NGC numbers, or IC numbers for the Caldwell objects, the appendix that gives these and specifications for the Caldwell list might better have been used as a table of contents for the main section of the book, but there is a convenient quick guide to the objects, without common names, inside the back cover. O'Meara provides his own list of twenty additional objects for observation as well as a convincing explanation why Messier did not include the Double Cluster in his catalogue. Also included is an informative essay by Larry Mitchell on the indefatigable observer William Herschel. The book is handsomely printed on heavy, clay-coated pages, weighing in at about twice the Messier book's heft.
What most observers discover, I believe, when they turn their attention to the Caldwell list, is that they have already seen the spectacular objects on it such as the Veil Nebula, Omega Centauri, the Helix Nebula, the Ghost of Jupiter, the Ringtail Galaxies, the Owl Cluster, the Eskimo Nebula, the North America Nebula, the Sculptor Galaxy, and a few others. Southern observers would certainly add the Eta Carinae Nebula, the Coalsack, the Tarantula Nebula, the Jewel Box, and one or two more. But when they look for the other objects in the list, they may find that the difficulty of observing them in small scopes may not be compensated by either beauty or interest. Some of us have always wondered, for example, why Walter Scott Houston seemed so fond of the globular cluster NGC 2419, the "Intergalactic Wanderer"; here it shows up again as Caldwell 25, and, as O'Meara says, it's not a "knock-your-glasses-off spectacle." But if anyone can convince you of the interest of the more difficult objects here while encouraging you to keep trying to find them, it's Stephen James O'Meara.
