Despite the proliferation of computerized go-to telescopes and planetarium software for notebook computers and PDAs, printed star atlases remain extremely useful. Many astronomers, for example, use star atlases to plan their observing sessions because they prefer the "big picture" of a printed atlas to the constraints of a relatively small notebook or PDA screen. Many also use printed charts during observing sessions, preferring their familiarity and reliability. (You'll never have to cut short an observing session because the battery in your printed atlas dies.)
There are numerous star atlases to choose from, and those atlases vary greatly in level of detail, scale, physical size, price, and other important considerations. Which atlas or atlases are best for your needs depends on numerous factors, including:
For example, a star atlas that is ideal for someone who observes bright star clusters from an urban location with a 3.5" refractor is poorly suited for someone who observes dim galaxies from a dark rural site with a 20" Dobsonian reflector, and vice versa.
Like many astronomers, we have both large and small instruments and observe from both urban and rural sites, so one star atlas is insufficient for our needs. The following sections describe the atlases we use, and our reasons for choosing them.
Mag 6 atlases, also called "naked-eye" star atlases, chart stars down to magnitude 6.5 or so. No amateur astronomer should be without a Mag 6 atlas. They're useful for impromptu naked-eye or binocular observing sessions, and for times when you simply don't feel like hauling out the "serious" charts.
Mag 6 atlases show only a few hundred of the brightest deep-sky objects, including (usually) all of the Messier Objects and the brightest non-Messier NGC objects, such as the Double Cluster, as well as prominent double stars. Mag 6 atlases use a small image scale, typically mapping the entire night sky on a dozen or so small charts. This small scale limits the number of objects that can be shown and the amount of label detail for each.
For example, Figure 1 shows the cluttered belt and sword region of the constellation Orion as shown on the Mag 6 Orion DeepMap 600 chart. Only the brightest stars and DSOs appear on this chart, and the small scale means that it can be difficult to determine which label refers to which object. This is not a slam on the Orion DeepMap 600; in fact, it's one of the better Mag 6 charts.
When you want just an overview of bright stars and objects rather than a detailed (and cluttered) view, a Mag 6 atlas is just what you need. We always have a Mag 6 atlas handy for that reason.
Figure 1. The belt and sword of Orion, as shown by the Orion DeepMap 600 (click on the thumbnails to view full-size images)
Here are the Mag 6 star atlases we use and recommend:
The next step up from a Mag 6 star atlas is Sky Atlas 2000.0 (Sky Publishing, 1999), which is considered by many amateur astronomers to be the gold standard among "serious" star atlases. Sky Atlas 2000.0, or SA2K, covers the entire sky with 26 charts drawn by, you guessed it, Wil Tirion. SA2K charts 81,312 single, multiple, and variable stars of magnitude 8.5 and brighter--which is to say, about nine times as many stars as a Mag 6 atlas--and about 2,700 deep-sky objects, including most of the Herschel 2,500 list. SA2K also includes supplemental detailed charts for the celestial poles, the Coma-Virgo galaxy cluster, and other cluttered areas. It also includes a transparent coordinate grid overlay that provides fields of view for finders, a Telrad, and eyepieces.
SA2K provides much more detail than a Mag 6 atlas. For example, Figure 2 shows the same region around Orion's belt and sword that is shown in Figure 1. Comparing the two figures, it's obvious that the SA2K chart is not only much larger scale, but includes many more objects and more detail about each object.
Figure 2. The belt and sword of Orion, as shown by Sky Atlas 2000.0 Deluxe (click to enlarge)
Many of the objects charted by SA2K are beyond the reach of a binocular or small telescope, even from a dark site. We have heard it said that a skilled observer with a 4" scope at a very dark site can observe all of the objects charted by SA2K. That may be true, but our regular observing sites aren't that dark (and, perhaps, we're not that skilled). We think SA2K is a perfect match for a typical intermediate to advanced amateur astronomer who uses a 6" to 10" telescope from what passes nowadays for a dark site.
If SA2K sounds good to you, the next decision is which version to buy. SA2K is available in six versions:
Both Field Versions use white stars on a black sky, mimicking the appearance of the night sky. The rationale of using these mostly black charts in the field is that they minimize glare and make it easier to remain dark-adapted. In reality, if you use a proper red LED flashlight for viewing charts, your dark adaptation is unaffected, no matter how bright the red light. The downside to the Field Version is that the black background makes it impossible to annotate the charts or to draw in constellation lines, which are not printed on the charts. The two Desk Versions are identical to the Field Versions, except the Desk Versions use black stars on a white background, which we greatly prefer.
The Field and Desk Versions are available either as loose paper charts, at $30 list price, or as laminated, spiral-bound books, at $70 list price. Despite the higher price, many amateur astronomers buy the laminated versions because they are immune to dew, which can quickly wreck unprotected paper charts. We dislike the stiffness of the laminated versions, and prefer to use a standard version and take steps to protect it from dew. The easiest way to do that is simply to cover the charts when they're not actually being used. Covering them with a towel will protect them adequately under all but the worst dewing conditions. Alternatively, Sky & Telescope sells a $28 chart carrier that is specifically designed to carry and protect any version of the SA2K. The chart carrier includes a protective plastic sheet that allows you to view any particular chart while keeping it dry.
Unlike the Field and Desk versions, which use monochrome 13.5" by 18.5" charts, the Deluxe versions use full-color 16" by 21" charts. In addition to making them prettier, we think the use of color adds significantly to the usability of the charts. (The charts are equally readable under white or red light.) The $50 Deluxe Version is spiral-bound into a 12" by 16" book, with each chart folded once. The $120 Laminated Deluxe Version is also spiral-bound, but without folding, yielding an oversize 16" by 21" book that we consider too awkward for use in the field.
On balance, we think the unlaminated Deluxe Version is the best choice for most people. Despite extensive use in the field, our copy remains in good condition, without any dew damage.
The only missing piece in Sky Atlas 2000.0 is an index of the objects it includes. That lack is remedied by the Sky Atlas 2000.0 Companion ($30; Sky Publishing, 2000; ISBN 0933346956) by Robert A. Strong and Roger W. Sinnott. Its nearly 300 pages list and describe each of the 2,700 DSOs charted by SA2K, and cross-reference each object by chart number. We don't use this book, because we generally work with standard catalogs such as the Herschel 400, which list objects by declination and right ascension, making it easy to locate the object in the SA2K charts. But if you want to locate objects in SA2K using only their NGC or other standard designations, the SA2K Companion is essential as an index to the charts.
If Sky Atlas 2000.0 is the gold standard in serious star charts, then Uranometria 2000.0 (U2K) must be the platinum standard. As useful as SA2K is, it doesn't go deep enough for many serious astronomers, particularly those who observe with larger instruments from very dark sites. If your scope is at least 8" to 10" and you observe from a reasonably dark site, you'll see many prominent objects that don't appear in SA2K. Welcome to the world of serious DSO observing.
Dedicated DSO observers consider Uranometria 2000.0 their bible. Uranometria 2000.0 charts 280,000+ stars down to magnitude 9.75 and 30,000+ deep-sky objects. That's more than three times as many stars as SA2K and more than ten times as many DSOs. In a region where SA2K charts two or three galaxies, for example, U2K may chart 20 or 30. U2K also includes 26 even more detailed charts of cluttered regions, with a limiting stellar magnitude of about 11.0.
With the exception of the Millennium Star Atlas, now out of print and selling for $500 used, U2K is by far the deepest mainstream printed star atlas available. And, although MSA goes deeper than U2K for stars, U2K goes much deeper than MSA for DSOs. The only close competition for U2K is the Herald-Bobroff AstroAtlas. Some observers like the HBA, but we consider it too cluttered for use in the field.
Figure 3 shows the same region around Orion's belt and sword in U2K shown in Figure 2 for SA2K. At first glance, the level of detail may seem similar, but closer examination shows that U2K provides significantly more detail than SA2K. Look, for example, at the region between Alnitak and Alnilam, where many more stars are visible on the U2K chart. Also examine the region of the Great Orion Nebula, where U2K again provides immensely more detail.
Figure 3. The belt and sword of Orion, as shown by Uranometria 2000.0 (click to enlarge)
Uranometria 2000.0, by Wil Tirion, Barry Rappaport, and Will Remaklus, is packaged as a three-volume set of hardback books. Uranometria 2000.0 Deep Sky Atlas Volume 1 ($50; Willmann-Bell, 2001; ISBN 0943396719) covers the northern hemisphere from declination +90° to -6°. Uranometria 2000.0 Deep Sky Atlas Volume 2 ($50; Willmann-Bell, 2001; ISBN 0943396727) covers the southern hemisphere from declination -90° to +6°. Both of these volumes are necessary for complete coverage of the night sky. Uranometria 2000.0 Deep Sky Field Guide Volume 3 ($60; Willmann-Bell, 2001; ISBN 0943396735), by Murray Cragin and Emil Bonanno, lists and indexes every DSO charted by the two atlas volumes. Each of the 220 double-page charts in the atlases has a corresponding table in the Field Guide that lists co-ordinates, dimensions, classification, and notes for every object plotted on that chart. The Field Guide also includes a full index that lists every object and is cross-referenced to the appropriate chart number. All volumes are printed on high-quality paper. Although they are not dew-resistant, taking minimal precautions such as closing them when not in use will keep U2K in good shape through years of field use.
The real decision in choosing printed charts is where to stop. Even the deepest printed charts cannot plot every object visible in large scopes from dark sites, so at some point most dedicated DSO observers find themselves abandoning printed charts for planetarium software, which has no such limits.
For most observers, we think Sky Atlas 2000.0 is the ideal compromise in terms of depth, cost, and usability. We observe primarily with a 10" scope from reasonably dark sites, and find that SA2K is a good fit in terms of objects plotted versus objects visible with our equipment. When we observe from a darker site or with a larger instrument, we use our notebook computer running Xephem or Cartes du Ciel to chart the truly faint fuzzies or beg a few minutes with an observing buddy's copy of Uranometria 2000.0.
If you observe mostly faint DSOs from a dark location with an 8" or larger scope, and particularly if you don't have a notebook computer you're willing to risk in the field, don't bother buying SA2K. You'll be much happier with Uranometria 2000.0.
Robert Bruce Thompson and Barbara Fritchman Thompson are experienced amateur astronomers, co-founders of the Winston-Salem Astronomical League astronomy club, and the co-authors of several O'Reilly books, including Astronomy Hacks, Building the Perfect PC, PC Hardware Buyer's Guide, and PC Hardware in a Nutshell.
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