The history of amateur astronomy in the last century can be told in terms of star atlases available to the amateur. Until 1950, the interest was in stars, and that was primarily what atlases depicted. My old 1954 Norton’s has a full page of double stars listed for each of 8 double-page charts, close to 400 in all, but a grand total of only 76 "nebulae and clusters." Many more deep sky objects are plotted on the charts, including all the Messier objects and a large number of Herschels, but the latter are designated using Herschel’s original eight fold classification, based on telescopic appearance rather than the objects’ real nature. NGC numbers appear only in the tables of suggested objects, and all the deep sky objects are represented by a single generic symbol: an asterisk-like grouping of seven dots.
In the late ‘40s. Walter Scott Houston started writing his column "Deep Sky Wonders" in Sky & Telescope, encouraging amateurs to seek out objects beyond our local stellar neighbourhood. About the same time, Antonin Becvar in Czechoslovakia produced a new atlas, named Skalnate Pleso after his observatory. The charts were larger, more numerous, and on a larger scale, showed much fainter stars, but, best of all, used different symbols in varying sizes to distinguish between open and globular clusters, planetary, diffuse, and dark nebulae, and galaxies. More deep sky objects were shown, many now labelled with their NGC and IC numbers, though fainter ones remained annoyingly anonymous. Wil Tirion’s popular Sky Atlas 2000.0, which first appeared in 1981, is a fine continuation of this tradition.
The arrival of large inexpensive Dobsonian reflectors in the early ‘80s brought another revolution. Observers were soon penetrating way beyond the "easy" objects in the atlases of the day, and the time was ripe for new atlases that went deeper. The pioneer in 1987 was Uranometria, fusing the cartography of Wil Tirion, the computer skills of Barry Rappaport, and the historical perspective of George Lovi. It offered more stars, more deep sky objects, and much larger scaled charts, and soon became the deep sky observer’s standard reference. Its main defect was a very confusing arrangement of the chart sequence, involving many page turns while starhopping across the sky.
Uranometria was joined in 1994 by the Herald-Bobroff Astroatlas, not as well known as the others because of its Australian origin, which carried the idea of symbols for deep sky objects to an almost ridiculous extreme, and added the useful concept of larger scaled charts for complex areas of the sky. Finally, in 1997 the European Space Agency and Sky Publishing produced the massive Millennium Atlas, by far the largest and most expensive to date. Millennium improved the accuracy, scale, and included a larger number of fainter stars made possible by the Tycho/Hipparchus project. All three atlases are distinguished by a move from a relatively small number of very large charts, to a large number of charts bound into one or more volumes.
Rather than repeat their 1987 efforts, the editors of the new 2001 edition of Uranometria (which I’ll call "Uranometria2") have absorbed the best ideas of their competitors and responded by producing something almost entirely new. Instead of a single set of 473 one-page charts, all the same scale and arranged counterintuitively by increasing right ascension, they have gone to a smaller number of 220 two-page charts, arranged by decreasing right ascension, so that the sky continues from the right side of one chart onto the left side of the next. They have supplemented these 220 basic charts with a 22-page mini-atlas at the front of each volume, plus 26 larger scale charts for areas where objects are too dense to plot on the scale of the main charts. This is a compromise between the 1548 uniform scale charts of Millennium and the six different scales found in Herald-Bobroff. Finally, they have beaten every other atlas out in the "faint fuzzy" sweepstakes, by including three times as many deep sky objects as any previous atlas.
Let’s look at a typical 2 degree square area centered on the Leo Triplet: M65, M66 and NGC3628. Norton’s shows just three galaxies in this area. Skalnate Pleso shows these three plus two more, but only labels three of them. Most later atlases, including Uranometria and Millennium show six or seven galaxies. Herald-Bobroff shows 13, and the Uranometria2 20!
What are the down sides to the new edition? The switch from 473 single-page charts to 220 double-page charts, while it greatly simplifies navigation, makes the new chart numbers completely incompatible with the old, which are widely quoted in many reference books. And it isn’t just a matter of converting chart numbers: the actual boundaries of the charts in the two editions are quite different. I’ve become used to the large chart scale of Millennium; Uranometria2’s smaller scale charts seem cramped. The star dots themselves are smaller than in any of the three earlier atlases, making them harder to see under dim red light. The large number of newly added faint galaxies may be a boon to the owners of gigantic Dobs, but really clutter up the charts for us more modestly equipped deep sky explorers.
The newly added objects go far beyond the lists generally available to amateurs. To provide reference material on these faint objects, Uranometria2 has expanded the Field Guide, available as a separate volume from the two volumes of charts. For each of the 220 charts, the Field Guide lists all the deep sky objects plotted within the (non-overlapping) boundaries of that chart, so that each object appears under only one chart heading. For any one chart, there are separate lists for each category of object giving newly measured coordinates, dimensions, classification, and notes. These are all cross-indexed in the back for a total of 25,895 galaxies, 671 galaxy clusters, 1,617 open clusters, 170 globular clusters, 14 star clouds, 377 bright nebulae, 367 dark nebulae, and 1,144 planetary nebulae; 30,255 objects in all! Having this material in paper form is useful, but I hope that it will be made available digitally as well.
So, is this now the star atlas of choice? For the very serious and well-equipped
deep sky observer and imager, the answer is definitely yes. It will serve
as a prime reference for some time to come. It is outstandingly well done.
For the rest of us, I’m not so sure. I’ve been hard pressed to find most
of the objects plotted in Sky Atlas 2000.0 in my Ontario skies.
But then, atlases, whether of Earth or sky, have never been tied to day-to-day
reality for me...they are the stuff of dreams! Maybe when I retire to Arizona...
Geoff Gaherty has been a star atlas junkie since he bought his first Norton’s in 1957. Until now, his favourite has been the Millennium, with whose help he recently completed his Finest NGC Certificate.