review: The Firefly Planisphere Deluxe

I mentioned ordering this thing before the holidays. Now I've got it;
here's my review...

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 weight it yet). (For those of you who find this package
too bulky, Firefly is slated to produce a 10-inch version in February
2004.)

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 planisphe 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, space permitting, 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. [1] 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."

Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

[1] 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