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Sky & Telescope's new Pocket Sky Atlas

Posted by Warren Bitters   04/29/2006 12:00AM

Sky & Telescope recently published a new sky atlas called Pocket Sky Atlas (PSA), with a list price of $19.95. PSA is designed to be extremely portable while including enough stars and deep sky objects to be useful. It succeeds in achieving these goals. I have been a regular Sky Atlas 2000 (SA) user for many years, but I decided to purchase PSA after skimming a copy of it at our astronomy club’s most recent meeting.

The atlas measures 9 inches tall by 6 1/2 inches wide. It contains 80 maps, arranged as eight strips of ten maps. Each strip covers three hours of right ascension. The first and last maps of each strip cover the north and south polar regions, respectively. The middle eight maps of each strip display the region in progressively lower declination. The breakdown is as follows: first polar map displays declinations north of +60 degrees; first pair of maps covers declinations between +30 and +60; second pair of maps covers declinations between 0 and +30; third pair of maps covers declinations between 0 and -30; fourth pair of maps covers declinations between -30 and -60; second polar map displays declinations south of -60 degrees. Despite having 80 maps, navigation is easy, thanks to the fact that each strip contains ten maps. Each strip begins on map #1, #11, #21, etc. You simply divide the RA you want by 3 to know where to start, i.e. RA 12 (12 divided by 3 equals 4) starts on map #41. As an additional navigational aid, the edges of each map indicate the map number where that section of the sky continues. This is a nice feature. Despite the small size of the atlas, each map also contains a reasonable amount of overlap, which aids in usability.

The atlas plots about 30,000 stars to visual magnitude 7.6. The selection criteria for nonstellar objects depends on the visual magnitude and type. For instance, the atlas plots galaxies to magnitude 11.5, globular clusters to magnitude 10.5 and planetary nebulae to magnitude 12. The atlas plots all objects in the Herschel 400 list even if they would have been rejected by the standard selection criteria. The atlas also includes symbols and labels for double, variable and carbon stars.

Since I am familiar with Sky Atlas 2000.0 and since many readers who would consider purchasing PSA may also use or be considering SA, I have compared and constrasted these two atlases below.

PSA features constellation outlines in a nice light green color, while SA does not. In the past, I have spent hours with pencil and ruler neatly drawing constellation outlines into my SA, so I appreciate this feature very much.

Despite showing fewer deep sky objects overall than SA, PSA shows many objects that SA does not. For instance, map #1 includes the Cassiopeia open clusters NGC 136, NGC 381 and NGC 436 not shown in SA. While far from a comprehensive list, other fine deep sky objects shown in PSA but not in SA are planetary nebula NGC 1360 in Fornax and open cluster NGC 6791 in Lyra.

PSA includes limited double star labels. For instance, map #1 includes Struve 3062, Struve 163 and Struve 460. As a double star observer (and moderator of the Astromart Double and Variable Star Observing forum), I appreciate the addition of these labels. SA does not include double star labels. Hard core double star observers will undoubtedly find the number of labeled double stars to be insufficient but, in my opinion, for a sky atlas of this scope the editors appear to have done a good job.

On the subject of object labeling, PSA is very generous. Some might argue it is too generous. The maps contain so many labels that they appear somewhat cluttered. In some cases, the extra labeling is helpful. For instance, map #13 informs the reader that NGC 869/884 is the Double Cluster and the sequence of stars northwest of NGC 1502 is Kemble’s Cascade. However, in a case of overkill, it shows that Stock 23 is also known as Pazmino’s Cluster. That label starts in Camelopardalis, cuts across a corner of Cassiopeia and ends at the Double Cluster in Perseus. Let me be clear, however. The generous selection of stars and deep sky objects plotted and the comprehensive and informative labeling is very well done. Only occasionally does too much of a good thing become not a good thing.

PSA contains a comprehensive index that includes star names, all plotted deep sky objects sorted by type and separate listings of Caldwell and Messier objects. Of these items, SA’s index only includes star names and Messier objects. However, SA’s index includes the constellations. Strangely, PSA’s index omits constellations. Beginners who are less familiar with the locations of the constellations may find this omission problematic but intermediate and advanced users will have no trouble navigating the atlas.

PSA uses fairly thick stock glossy paper for the maps. Unfortunately, and this is a big problem, it uses flimsy paper stock for the cover. It seems likely that PSA will not fare well with heavy usage in the field. In contrast, SA uses a thick plastic cover. PSA would have benefited from similar attention to sturdiness.

In conclusion, PSA is a well executed sky atlas. For myself, PSA will be more useful as a planning tool than as an observing aid in the field, especially since the atlas’s potential durability is suspect. However, part of that assessment is due to the fact that I am an ardent Sky Atlas 2000 user and it is hard for old dogs to learn new tricks. I expect there are plenty of amateur astronomers who would find PSA to be a perfectly sufficient sky atlas for both planning and field use.