The Map_BSC program plots maps using a modified The Bright
Star Catalogue [8], which I offer as a package
with files of *.dbf
type. (Since 1999, it can use large Hipparcos or huge Tycho star catalogue
instead [9].) Apart from B5_cd.dbf (or hip_main.dat or
tyc_main.dat) file it can use another database files,
which I offer as Sol_Syst and Litt_Atl packages. Maps
produced using the Bright Star Catalogue are sufficient for observation
without a telescope, and
they can serve even for finding bright comets with binoculars. An example,
not much edited from the automated output, is
Malý hvìzdný atlas
(A Little Star Atlas)
in the Czech book
Bájeèný svìt hvìzd
(A Wonderful World of Stars).
The program is able to produce very diverse outputs, depending on a number of parameters. It may take some time to tune the output to your needs. Especially complicated it may be in the case of cometary heads and tails.
Several configuration files *.cnf and batch files mb*.bat,
shipped together with the source code, could be a good starting point for
you. To understand them, you may use the overview of the parameters of
Map_BSC, which you obtain running the programme with a h
and then with a $h option (or simply by running mb_hfile.bat)
-- file map_bsc.hlp is produced this way.
Using Hipparcos data [9] instead of the Bright Star Catalogue
enables to print ten times more stars and to get true stereoscopic charts
(parallaxes in the ground-based Bright Star Catalogue are often
much in error) [17]. With huge Tycho catalogue, maps
containing all stars visible with small binoculars can be made,
including precise photometric information.
The program can be considered a graphic batch viewer of these two large
catalogues, which displaying any infomation from them. In case of Tycho,
a subset of data (e.g., one third in size, as those made by tyc_sel
programme) can be used for input as well.
``Rotating charts'' or planispheres are common as planar circular structures; however, the programme enables to make conical maps (which become really conical, when their ends are glued together) and straight belts as well. Their purpose is always the same: to show, which stars are over horizon, and to demonstrate, how they rise, move and set. The following explanation is meant for those people, who really print the maps and masks using the prepared batch files.
It may seem obsolete to make paper toys like that, when computer can show you the sky at any moment and any place on the Earth. However, the computer is not so easy to hold in front of you under the open sky. And the resolution of the screen is far inferior to the resolution of advanced printers.
To make a pair of plain turnable charts for a latitude of, say, 55
degrees, run mb_ns_ch f55. It will prepare and print (if you are
using GhostScript)
four sheets: north-pole-centered map (equidistant in
declination), south-pole-centered map (stereographic) and zenithal grids
for these maps. Cutting, folding and gluing will provide you then with a
turnable star chart with one face for an all-sky view, but much distorted
near to south, and another face for looking at the southern horizon
without much distortion. See further section for detailed instructions
regarding the assembly.
To make a conical map with a turnable mask, use mb_c_ch.bat. It
will produce two sheets to be cut in an obvious way and glued to make real
cones (just bottom part, in case of a mask). A pair of a conical mask and
achart has an advantage, than no special folding is necessary to center
the mask properly: the conical shape does it itself.
To get a map with no bias toward one or the other celestial pole, run
mb_e_ch.bat. It will produce four sheets. Three of them are maps;
they should be cut along the lines corresponding to celestial poles and
then glued together to form a single long map with stars repeated two
times. The remaining sheet should not be cut but folded along these lines
of declination plus and minus 90 degrees, to fit around the prepared long
map. Then its face part should be cut (preferably by a razor on a
cardboard) along the horizon line and then along the marginal lines above
the horizon, till the upper fold. It becomes the mask then. Insert then
the long map belt there and shift it to match the sky at the wanted
moment.
If you happen to live near the latitude 49.2°, you can use the
prepared maps in the astro\map_bsc\maps directory. Otherwise, you
should run the batch mb_ns_ch with appropriate latitude parameter.
Take the four resulting sheets and view
them. To save you experimenting with proper cuts, folds and gluing, I
recommend you the following procedure.
First, your printer may distort the picture, what is bad especially in the case of the border circle. To correct or check it, take a compasses and make a circle centered at the pole; the circle should be just slightly smaller than the printed one.
The hole you have made in the pole will then help you to align the two maps back to back properly. Properly, it means with the stars to opposite directions. Stack the maps on the window and match the poles; the rims of paper should remain parallel. Press the left half of stacked sheets firmly against the window, bend the right half ot the top sheet left and put some glue sparsely on the the bottom sheet, just a band some one centimeter wide along the border circle. Press the top sheet quickly there, so that the bottom sheet gets no more wet than the top one. When it holds after some five or ten seconds, repeat the procedure with the other half of the sheets. Then you may cut it along the border circle.
The two masks should be handled differently. The southern one (stereographic, with all curves being circular arcs) should be cut along the straight lines, and then along the horizon (or very slightly outwards). The ``clock face'' will remain on the resulting part.
The northern mask should be not cut but folded around these straight lines. Cutting the northern mask is a bit more complicated. Cut it along the other straight lines, prolong cutting along the border circle, and continue along the curve of an angular height of -30 degrees. Then the inside part of the mask is to be cut away: along the horizon, of course, so that the ``clock face'' will be discarded; you may wish to cut a bit more inside, to leave azimuth marks intact.
The two masks are then to be glued together in an obvious way: put the southern one inside the folded northern one, center it properly (to compensate for possible printer distortions), and glue the folded part of the northern mask onto the southern one.
Then you can insert the two-sided map into the pocket formed by the masks (northern map should be under the northern mask), align the month (or its proper part) on the map with the time (local, not ``summertime'') on the mask, and you will see which stars are over horizon.
If you prefer to join the pair of maps with their masks permanently, print the four sheets once more, and cut the northern mask along four tangents * of the marginal dashed circle. Cut it in the cusps till that circle, and fold the halved cusps over the inserted pair of maps. Gluing the halves of cusps together will make the charts permanently masked.
Of course, hard paper will do a better job than an ordinary one; laser printers are adapted in seconds to print without bending the paper, and can tolerate quite thick sheets (consult the manual) -- they should just have smooth surface to accept the paint.
Parameters s and sc or sm enable generating
pairs of maps, which can produce an illusion of a 3-dimensional
scene: just one map, showing the various objects in various
distances. However, if you are not experienced in viewing stereo
images, you may find it difficult to reach such view at all,
not to speak about viewing the 3-D image comfortably.
The impression of the depth is attained in such a way, that the stars in maps for the left and right eye are shifted in various extent with respect to each other, according to their distance from the Earth. The lines connecting the stars with the appropriate eyes are to be more convergent for the near stars. This convergence is called parallax. 'Astronomical parallax' concerns the case, that the 'eyes' are one 'astronomic unit' apart, or some 150 Gm. Astronomical parallaxes of fixed stars are smaller than one arcsecond. For the stereomap to work, the plotted parallaxes are to reach some tenths of a degree for your true eyes.
A comfortable view can be attained in such a case, that the convergence of the eyes corresponds to their focusation (accomodation). A perfect match can hold just for the only apparent distance, preferably for distant stars with almost zero astronomical parallaxes. Stars with a larger parallax seem to be closer, but the eye accomodation is unchanged, as in reality all stars are plotted in the same plane. This is the reason why no stereogramme reaches the quality of a hologramme, and why viewing means always some eyestrain.
The match of convergence and accomodation for distant stars can be reached by using suitable glasses. For example, if the distant stars are plotted in the same distance from each other as the mutual distance of your eye pupils is (say, 65 mm) and your face is some half meter from the screen, you need to strengthen the dioptric power of your eyesight by two diopters. You should use glasses with convex lenses of this power, or with the focal length of fifty centimeters. Such glasses are common, quite a lot of elderly people use them for reading. If you would have just glasses having four diopters, you should watch the maps from a distance of a quarter meter. Majority of stars would appear in a large distance and just the closest stars would emerge as near to you.
If you take glasses having two diopters (or, as myopists, you put off your glasses of -2 D) and you want to watch the map from a distance less then 50 cm, you have to use another base shift of star pairs. For a viewing distance of 25 cm the shift should be just half of your eye baseline (just some 32.5 mm), otherwise the view would be painful. In such a situation you have no impression of a distant universe, but you see most stars as if being in a plane half a meter from you, and just some dots are perceived nearer. These are more difficult to see, due to the non-matching convergence and focusation. You can see them better, if you get close, but then the view of the more distant stars becomes less pleasant.
Anything outside the map disturbs the view, so it is preferable hide everything else from your sight. If you are watching black-and-white maps, it is nice to separate the maps by a black (in case of a computer screen) or white (for printed maps) cardboard going till your face, so that each eye sees just one map. If the maps are to match each other, their width is to smaller then the mutual shift of the distant stars. (75 mm at most).
An alternative of glasses is a mirror, which replaces also the
piece of cardboard in separating the maps. In this case one of
the maps is to be mirror-reversed (my programme can do it for
the left map). The advantage is that the 75 mm width limit is
overcome this way, as the maps can stretch far away from the
mirror. (To make the map wider, you can set the second item
in the stereo geometry parameter somewhere near to two hundred,
e.g., as s30:190). (This mirror option is an idea I saw
in the examples published in November 1999 on the Hipparcos
pages [9].)
If using red and green (or blue) colour (parameter sc),
the maps can overlap each other. The necessary aid are colour
glasses, filtering perfectly both colours (if the filtration is
not perfect, there remain unpleasant ghosts). They can be
bought, e.g., from [18]. The dioptric glasses can be
made obsolete in this case, if you choose the base shift as zero
or very small (e.g., by giving s20:2).
