Title: The Firefly Planisphere Deluxe, by Storm Dunlop and Wil Tirion
List price: about $40 U.S.
Published 2003 by Firefly Press
ISBN 1-55297-786-2, with 24-page booklet
I've written previously in praise of the planisphere. It is a quick and lightweight way to find out what is up in the sky at any time of night, it never needs batteries (other than perhaps a light source to read it by), and it also can help you to learn how the night sky moves from hour to hour and month to month. It gives you a tactile connection to the night sky that computer programs cannot. I don't think any amateur astronomer should be without one.
To be sure, not all planispheres are created equal. Some are paper, some are plastic, some are a bit of both. There are planispheres that show light-colored stars and constellations on a dark sky; there are planispheres that show them the other way around. There are planispheres that show not only how the sky looks now, but how it will look thousands of years from now as the Earth's axis precesses.
One of my favorite planispheres is the Chandler planisphere, which makes good use of the fact that a planisphere is flat. All planispheres are adversely affected by the distortion created when the sphere of the sky is projected onto a flat piece of paper or plastic, but the Chandler planisphere is the only one I know of which takes advantage of both sides of a flat planisphere. The further away a constellation is from the celestial pole, the more distorted it is. Since a typical planisphere shows some constellations down to perhaps –45 degrees declination (three-quarters of the way to the opposite pole), the constellations on the outer edge of the wheel are significantly distorted.
The Chandler planisphere gets around that by printing constellations on both sides: the northern ones on one side, and the southern ones on the other side. (There's a small amount of overlap, so that equatorial constellations such as Orion don't get sliced in half on both sides.) To see what's in the sky toward the north, you look on the northern side; to see what's up in the south, you flip the planisphere over. The dials are carefully set so that you don't have to adjust the planisphere at all—you just turn it over. It takes a bit of getting used to, but once you do, it works very well indeed.
As nice as it is, the Chandler planisphere has a few drawbacks that keep it from being the ideal specimen—for me, at least. The map disc is made of paper, rather than plastic (the sleeve is plastic, though); also, the thing is a bit too small. (Even the large edition is only 9 inches across.) Probably in large part for that reason, there are just too few stars on it for me to do much with it beyond getting my general bearing.
Now, a new planisphere has stepped into the fray. Designed and executed by Wil Tirion, the leading light of stellar cartography, the Firefly planisphere is a work of art. The moment you pick it up, you can tell it's substantial. The map disc is thick and large: 15 inches across, and about a millimeter thick. The planisphere as a whole weighs several ounces (I haven't weighed it yet).
The printing is also quite fine. The large size of the planisphere allows it to be marked to substantial precision. The outer edge of the map disc has not only the date dial (against which the hour dial on the planisphere's mask is matched), but also a right ascension dial. This is marked to the nearest minute of right ascension: 1,440 marks going around the outer edge of the planisphere. Constellation labels on the map itself are small—about as tall as the disc is thick—yet clearly readable. Also included are the classical stick figures and the modern constellation boundaries.
That leads into another main draw of this planisphere: the wealth of information readily available on it. The large stellar database is only the beginning of the story: all stars down to magnitude 5.5 and north of declination –50 degrees. (That gets you down to just past omega Centauri!) It's the other objects shown that are the real forte of this item: all of the Messier objects, plus quite a few NGC objects outside the Messier catalogue. All galaxies are shown with their proper orientation and, where their size permits, their proper sizes and aspects as well.
Stars are color-coded according to spectral class, with the colors exaggerated to make it easier to distinguish them. All stars with Bayer (Greek letter) designations are labelled as appropriate, as are a great many with Flamsteed numbers. If you didn't know which star was 61 Cygni (Bessel's star), the Firefly planisphere will show you. Also marked on the map are the celestial equator and the ecliptic, as well as the basic outline of the Milky Way. (The sky of the planisphere is a medium light sky blue, with the Milky Way shown in lighter blue.)
The mask, whose purpose is to obscure the stars except those up in the sky, is also a work of ingenuity. The planisphere is designed for latitudes between 40 and 60 degrees north, a wide range, but unlike the Levy planisphere, which is a bit larger and covers a similarly wide range of latitudes, the mask is not simply set for a latitude in the middle of the range. To make it more precise, the mask has three separate horizon lines—one for 60 degrees, one for 50 degrees, and one for 40 degrees. This makes it easier for those living at intermediate latitudes to figure out which stars are just rising or setting at any given time.  The mask even has two hour dials: one for standard time, and another for daylight savings or summer time.
In addition to these two standard components of the planisphere, the Firefly planisphere has a third component: a pointer, calibrated with a declination line (marked to the nearest degree) and the analemma, too. The declination line can be rotated freely from the map and mask, allowing you to measure the declination of any star. The analemma can be used to find out more precisely the time of sunrise and sunset. The procedure for doing so is a bit complex, but is described in detail in the accompanying 24-page booklet, written by noted author Storm Dunlop.
Of course, the booklet covers all the other functions of the planisphere. It also has a section describing the various types of objects plotted on the planisphere. For those objects that cannot be plotted—the planets—the booklet gives the celestial coordinates for each planet at any time from 2003 through 2006. By using the right ascension dial on the map disc, and the declination markings on the pointer, one can easily pinpoint the location of any of the planets—except Pluto, which cannot be located without a much more detailed map—plus the asteroids Ceres and Vesta, to within perhaps half a degree. (The booklet does have a few minor typos that might confuse the beginner. For example, when describing the calibration of the stellar magnitude system, the authors write "Vega, or Lyrae." What they really mean is "Vega, or alpha Lyrae," but the Greek letter was accidentally omitted.)
In short, the Firefly planisphere has just about everything one could hope for in a planisphere, except it doesn't employ the clever trick of the Chandler planisphere to reduce distortion. It does use a slightly non-standard projection to strike a balance between maintaining recognizable constellation shapes on one hand, and commensurable constellation sizes on the other. But why not use the Chandler trick of using both sides of the planisphere?
It's because, as it happens, the other side of the Firefly planisphere is already used up—with a second star map, this one to a slightly larger scale, not in full color, and showing all stars to magnitude 6.0 above –50 degrees declination. It's just about a fully functional unaided-eye star map! Because it only employs blue and black ink on a white sky, this map is easier to use under a red flashlight than the front map, which in particular has purple constellation lines and orange galaxies. (Both the lines and the galaxies are, however, still visible in the dark under my red flashlight.) One can use the front side to see at a glance what objects are above the horizon and visible, and then proceed to the reverse side to star-hop or fine-tune the pointing of a telescope. The printing on this side is not quite as nice as the front side, with the constellation and declination lines especially showing some aliasing effects, but they don't noticeably affect the use of this map, only its aesthetics. They are an artifact of the printing process; the inside cover of the booklet shows a sample of the map that doesn't exhibit the aliasing.
It's impressive to me that all this functionality (a) can be squeezed onto a 15-inch disc, and (b) costs so little, relatively speaking. Yes, it is expensive as planispheres go, but only because so much work went into its making, and because you can get correspondingly much information out of it. The list price is $40 U.S., but the street price is closer to $30. I've seen planispheres that go as deep in stellar catalogue, but without nearly as many DSOs or features, go for twice as much. And if, like me, you enjoy star maps on the face of it, you'll definitely want to get this one, because like John Keats's thing of beauty, it's "a joy for ever."
 At 40 to 60 degrees north, the latitude range is a bit on the high side. It comes about because the planisphere was designed not for North America, but Europe as well. (The planisphere is printed in Germany by Franckh-Kosmos Verlags.) Much of the U.S. is, of course, between those latitudes.
Nonetheless, if you live outside of that range, as I do (at 34 degrees north latitude), you have a slight problem. In that case, the 40 degree horizon is close, but not quite right: the northern horizon will be shown too low on the planisphere, and the southern horizon shown too high. The former is not a difficult issue—one can simply draw a new horizon in that region of the sky—but the latter is more problematic, since the map disc simply doesn't have stars on it between -50 and -56 degrees declination. What to do?
There is a trick one can employ. Instead of showing all stars that are up at any given time, one can design a new mask that shows all stars that are at least 5 degrees above the horizon at any time, seen from a latitude of 35 degrees north. The exact shape of this horizon is not exactly an ellipse, because of the projection used to create the map, but an ellipse that is 7-5/8 inches by 9-13/16 inches is a convenient approximation. If you print or draw such an ellipse on a sheet of transparency, and overlay it on the planisphere such that (a) the minor or short axis of the ellipse coincides with the north-south meridian line of the planisphere, and (b) the northern edge of the ellipse is at a declination of +60 degrees, then your mask should just about show all the stars 5 degrees or more above the horizon from 35 degrees north.
It won't be exactly right—the eastern and western lines, in particular, will be too high off the horizon—but it will be close, and you'll be able to make better use of the planisphere, I believe.
Copyright (c) 2004 Brian Tung