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New Chart for Keener Eyes.

Sky Atlas 2000.0, Second Edition

Wil Tirion and Roger W. Sinnott (Sky Publishing and Cambridge University Press, 1998), 31 pages. Deluxe Version, ISBN 0-933346-87-5; $49.95. Field Version, ISBN 0-933346-89-1; $29.95. Desk Version, ISBN 0-933346-88-3; $29.95. Laminated Field Version, ISBN 0-933346-92-1; $69.95. Laminated Desk Version, ISBN 0-933346-91-3; $69.95.

Celestial cartography has come a long way since Sky Atlas 2000.0 appeared almost 20 years ago. In my review of the Deluxe Edition in the April 1982 issue of this magazine, I remarked that it was "more than adequate for the night-to-night requirements of the keenest observer." Today those keeners have moved on. Their computer-smart Schmidt- Cassegrain telescopes and monster Dobsonians are fed by large-scale charts not dreamed of two decades ago. But what about average enthusiasts with modest equipment? The second edition of Sky Atlas 2000.0 has come to their rescue.

Renowned star mapper Wil Tirion, in collaboration with Sky & Telescope associate editor Roger Sinnott, has produced an affordable atlas that is both elegant and rugged. The Deluxe Edition's heavy, dew-resistant cover protects 26 spiralbound, color star charts. The foldout pages are now numbered on the backs so that you no longer have to open a chart to identify it - an annoyance I noted in my 1982 review. The atlas also includes three helpful indexes listing constellations, Messier objects, and nearly 200 named stars.

Long-time Sky Atlas users will feel right at home with this edition. Featuring a scale of 8.2 millimeters per degree, the maps are slightly larger than in the original but cover the same swaths of sky. Tirion and Sinnott label 2,700 deep-sky objects (an increase of 200) and again provide a wide variety of double and variable stars. However, by extending the stellar limit by a half magnitude to 8.5, they have plotted more than 81,000 stars - nearly double the number in the first edition. Their positions and brightnesses were established using data from the recent Hipparcos astrometry mission.

And there's more. With the aid of computer graphics, the authors have graded the star dot sizes continuously instead of binning them in whole-magnitude steps. For example, the stars of the Big Dipper on chart 2 are denoted by six subtly different dot sizes that cover a range of only 0.65 magnitude (dimmer Megrez excepted). I agree with the authors that this ranking of brightness "should correspond even more closely to what the human eye sees."

The margin of each chart contains a row of reference dots in half- magnitude steps. I've always had trouble estimating magnitudes by comparing dots. However, the transparent coordinate-grid overlay provided with the atlas includes the same reference dots, allowing us to gauge stars directly by placing the plastic sheet atop a chart. The overlay also contains a handy Telrad finder bull's-eye.

The chart key again confirms that the map boundaries do not break up well-trampled hunting grounds. In fact, several interesting sectors, treated as insets in the first edition, have been relocated to the back of the atlas and magnified 211/42 times. These extras include the Alpha and Beta Centauri region, the area around Barnard's Star, and the Pleiades star cluster. Additional charts highlight both celestial poles, the central part of Orion, and the famous Virgo Galaxy Cluster.

The half-page spread on the Virgo Cluster caught my eye right away. This wonderful treatment of the "realm of the galaxies" boasts a slightly larger scale than the same area in Uranometria 2000.0, Tirion's landmark follow-up atlas. Moreover, the stellar limit extends to magnitude 10.5, which allows easier star-hopping for those of us who still do it! However, despite the extra room, the Virgo spread doesn't provide as many galaxies as are in Uranometria - a lost opportunity, in my opinion.

I liked Tirion's use of color in the first Deluxe Version and I find it even more helpful in this edition. The varying density of the Milky Way is delineated by four shades of blue - five, if we count the darkest patch marking the Sagittarius Starcloud. Yellow clusters, green nebulae, and red galaxies leap off the page. If you scan your charts with a dim red light, the red fill inside the galaxies' oval outlines disappears, but even the smallest ovals distinguish themselves from the star dots.

Deep-sky aficionados will also appreciate that the shapes and orientations of galaxies are depicted. This takes some of the guesswork out of identifying faint fuzzies - especially in that congested Virgo Galaxy Cluster. The custom symbols help sort out small galaxy groups, too. For example, "The Trio in Leo" is presented on chart 13 as two side-by-side vertical ellipses (the spirals M65 and M66) lying south of a nearly horizontal, narrow ellipse (the edge-on NGC 3628).

Inevitably, not every target survived the authors' selection criteria. For example, chart 9 plots the 11th-magnitude galaxy NGC 7332 in Pegasus but omits its 12th-magnitude neighbor, NGC 7339. The edge-on galaxies make a distinctive pair at high power in medium-size reflectors.

Nitpicking aside, Sky Atlas 2000.0 is a welcome addition to my collection of charts. I highly recommend it to the many amateurs who own the original and are considering a modest upgrade. It would also make a user-friendly companion to those upscale atlases favored by the keenest observers today.

Ken Hewitt-White observes from dark-sky sites in southern British Columbia. His introduction to stargazing for children, The Holographic Night Sky Book & Kit, will be published by Somerville House this year.
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Title Annotation:Review
Author:Hewitt-White, Ken
Publication:Sky & Telescope
Article Type:Book Review
Date:Jul 1, 1999
Words:914
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