Sky Atlas 2000.0 Second Edition

by Tom Polakis

Veteran sky watchers may remember the introduction of Wil Tirion's "Sky Atlas 2000.0" in 1981. At the time it was revolutionary, being the first star atlas to use Equinox 2000 coordinates. Inside a bound package measuring 11" by 16" were 26 charts covering the sky at a scale of 7.8mm per degree. The only suitable competition was Antonin Becvar's "Atlas of the Heavens," which over the years had revealed problems in need of repair. With its sweeping improvements, Tirion's work became the replacement for its predecessor, and took over as the standard intermediate-scale star atlas. 17 years later, the Second Edition of "Sky Atlas 2000.0" has been released. Its improvements on a classic are no less impressive than those we witnessed in 1981.

The second edition also employs 26 charts, but at a slightly increased scale of 8.2mm per degree. The dimensions of the atlas thus increase by 1 1/2" in width and 3/4" in height to provide identical sky coverage on each chart. As with the first edition, the atlas is available in the Deluxe Version, in which objects are plotted in color on a white background, and the less expensive black-and-white Desk and Field editions. The Desk and Field editions represent the sky a smaller scale of 7.1mm per degree.

At first glance the most desirable change in the second edition is its depiction of stars. The first edition plotted roughly 43,000 stars down to magnitude 8.0. This quantity is nearly doubled with the new edition's magnitude limit of 8.5. Much has happened in the star cataloguing business since 1981, and this is used to advantage by authors Wil Tirion and Roger Sinnott. Most significantly, the second edition employs the Hipparcos/Tycho star catalogues, which results in improved accuracy in stellar positions and brightnesses. Star symbols are plotted in a continuous range of sizes -- a big improvement on the whole-magnitude steps of the first edition. The increases in both depth and resolution should prove helpful to the observer intent on locating faint galaxies in sparse star fields.

For the deep-sky enthusiast, the second edition is vastly improved. The number of objects is only modestly increased from 2500 to 2700, but the selection criteria are more consistent. Fans of dull open clusters may be disappointed to learn that many of these objects were dropped from the database if they didn't meet the strict criteria for inclusion in the atlas. Galaxies are plotted as ellipses in their correct position angles. Dark nebulae from the catalogues of Barnard and Lynds are included, and large ones are plotted to scale. Milky Way contours are plotted in four levels rather than two. The transparent coordinate overlay presents a finer grid, and even includes the bullseye pattern of the popular 1-power Telrad finder.

It was irresistible to lay the first and second editions side by side. I found Chart #22 to be a suitable page for comparing the two editions. Centered on Sagittarius and Scorpius, this particular region of the sky can be prone to clutter. Less worthy cartographers than Wil Tirion have often met their demise in attempting to render this rich section of the sky. Inclusion of prominent dark nebulae in the second edition means that the Pipe Nebula so familiar to modern observers is shown in all its glory. Bright nebulae such as NGC 6334 that were simply "green boxes" in the first edition are outlined in correct shapes. The number of open clusters is glaringly reduced; for example the Stinger of Scorpius now contains 7, instead of 12, plotted open clusters. All planetary nebulae are labeled with NGC/IC or Perek-Kohoutek (PK) designations. Gone are planetary nebula designations such as Sp 1. While I didn't set out hunting for corrections from the first edition, they too been cleaned up. M24 correctly points to the small Sagittarius star cloud rather than a small open cluster in the vicinity. On another chart, the Vela Supernova Remnant is labeled as such, and not mistaken for the nearby Gum Nebula.

We find another good comparison by opening the two atlases to Chart #2. In the bowl of the Big Dipper, the multitude of faint galaxies will certainly be more easy to locate knowing their correct orientations on the sky and hopping from 8.5-magnitude finding stars. Over 200 star names are now included in the second edition. How many people would have known that Lambda and Mu Ursae Majoris are also known as Tania Borealis and Tania Australis? The double star catalogued as M40 has been plotted for those who feel compelled to complete the Messier list. All deep-sky objects are now labeled; the giant planetary nebula PK 164+31.1 in Lynx is an example.

General improvements in appearance are also laudable. The many lines and curves of celestial coordinates have a cleaner feel. The garish constellation boundaries of the first edition no longer get in your way and legends are more readable. Chart numbers are now accessible without folding out the page. And the confusing practice of the first edition of using a star-like dot to delimit different designations of the same object has been abandoned. All of these changes help when viewing chart under dim, red light.

Two brand new additions that appear in the second edition are Charts A and B, which feature selected areas as 2 1/2 times the scale of the other charts, and plot stars down to magnitude 10.5. The selected areas are great choices, featuring the fields of both celestial poles, the Virgo galaxy cluster, Orion, the Pleiades, and two high-proper motion stars. Again, these charts are a joy to peruse by day, somewhat like scanning over an inset map of your city in a road atlas of the country.

It is difficult to have any gripes with the second edition of "Sky Atlas 2000.0," but I do have one big one. I consider the backs of the charts to be a vast expanse of untapped space. I wished the authors would have taken a lead from Tirion's excellent, smaller-scale "Bright Star Atlas," and used the facing pages to provide catalogue data for all of the plotted objects. Perhaps it would have bumped the price up by another ten bucks, but it could have made this the end-all atlas of its scale. It would be a nice gesture for Tirion and Sinnott's to make their database available as a diskette or on-line, even if only as an ASCII text file.

Will I use the second edition of "Sky Atlas 2000.0" in the field? Well, no. I've discovered the joys of using a laptop computer and charting software at the telescope, and the advantages outweigh anything that a paper atlas could ever accomplish. Still, "Sky Atlas 2000.0" is a great enough piece of work to be enjoyed at the desk. For fifty bucks, there is enough in these charts to keep most observers occupied for a lifetime.