Star maps with xplns and xephem
For Linux astronomy, programs are available en masse. However, most programs are only used for research because Linux is very common in that arena.But hobby astronomy also has some useful Linux tools. Two programs are introduced shortly:
Maybe the best-known program to generate star maps is xephem. It is already available in version
3.2.2. and it has been constantly improved. But this program is able to do much more than just
drawing star maps as views of different planets of our solar system are included.
Very impressive is our moon which is overlaid with high res textures.If you wanted to investigate planets you would be able to see where the planets are in zenith. Now you could see if a planet was visible or behind the horizon.
With Xephem, star maps are generated easily. The program includes a big list of cities and everyone will find a place near them.
The positions of the stars are calculated with the included file, but if you wanted to use the actual data you would be able to download these automatically.
With a big option window, you are able to choose what you want to see. An additional filter makes it possible to reduce the shown stars by activating special criteria like brightness, the form of the galaxies, etc.
A very good printing output is also included (better than xplns). The prints can be either colored or black & white. Export to a postscript file is also supported.
Xephem is available as source code or as a pre-compiled binary file. The toolkit used is the
commercial library Motif. If you did not own this library you should download the
binary version. In it, the Motif libraries are statically linked and you do not need these
separately. But Xephem compiles with the GPL library lesstif, too, but lesstif has not been
100% compatible to Motif and sometimes display errors occur. This is not dangerous but can be disturbing. If you compiled Xephem with lesstif and linked the libraries dynamically the
program would be much smaller than the statically linked program.
Xplns
Xplns would be very useful if you wanted to generate actual star maps very fast.
The options for the different display modes are nearly all accessible using the button bar.
If you knew which function hides behind which button you would be able to generate star maps very fast.
The program has many weak points that cannot be corrected easily. Xplns has no GPL. The program
can be copied freely but is only available as a binary file.
The root of all this trouble is that the program owns parts of the "Stella Navigator"-code for M$ Win that is distributed commercially. To save this product, the source code of Xplns is not
available.
This is very bad because many important functions are missing in Xplns.
Other programmers could have implemented these without any problems if the source code had been free available.
The most missed option is the exportation of the star maps as a postscript file to print it.
If you do not had a laptop which you can take to you star observation you would have to use a
screenshot of Xplns to print the map.
The second missing option is the ability to add a new observation point to the existing list. This
default list is quite short and is mainly restricted to North America. If you wanted to add other
observation points you would have to edit the file "xplns.obs" by your own.
In the file xplns.obs you have to add an entry looking like:
Town-Description longitude latitude altitude Time zone(relative to GMT)For Hamburg we added:
Hamburg, Germany 9.800E 53.600N -1 +01.00Xplns takes care with the column sizes.
| Town-description | |
| longitude, 49th letter is an "E" for ea st or "W" for west | |
| latitude, 57th letter is an "N" for no rth or "S" for south | |
| altitude | |
| Time zone in hours, to the east with a "+", otherwise a "-" | |
| line-feed (\n) |
Also, it's nice that you can let the stars move on the sky and let them draw a line along the trajectory. It looks like the well-known picture of the star sky with a long shutter open time. You see that the polar star describes a small circle at the sky.
The display modes are the equator-, the horizontal- and the solar-system mode. With the last one you see the whole solar system and the stars behind in one overview.
You are able to choose the lowest magnitude used to display stars so beginners can start easily.
Galaxies and nebula are also displayed and, with a mouse click on the object, a window opens and presents additional information (Name, Magnitude, Angles, R.A., ...)
In particular, the easy handling of Xplns offers a better start for beginners than Xephem does. You see
your first star maps very fast and can easily play with the options.
Links:
Homepage Xephem:http://www.ClearSkyInstitute.com/xephem/xephem.html
Homepage xplns:http://www.astroarts.com/products/xplns/index.html
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