JSkyCalc -- A Convenient, Portable Observing Aid
John Thorstensen, Dartmouth College; 2008 July

Skycalc expedites the "time-and-the-sky" calculations needed by observational astronomers. The newest version, JSkyCalc, features:

System requirements are simple:

The Java Runtime Environment is automatically included in Mac OS-X, but if your OS is relatively old you may need to update to 1.5 or higher.

Click here to launch JSkyCalc with Java WebStart.

Alternatively, it is easy to install the program on your local system; this enables the reading of object lists and makes it possible to customize your site menu (with a little more work). Java provides a way of bundling up a bunch of files in an archive, called a "jar" file (much like Unix "tar"). Jar files can be executable:

Click here to download the executable jar file.

Jar files are independent of the CLASSPATH environment variable; if you stick it in a directory like /home/thorstensen/foo/bar, you can run it from wherever with the command

java -jar /home/thorstensen/foo/bar/JSkyCalc.jar
I'd recommend putting the JSkyCalc.jar file in an otherwise empty directory, in case you want to unpack it later.

Customizing the site menu.

If you want to customize your site menu, you'll need to unpack the jar file to get at the small data file that contains the site information. Go into the directory with the jar file -- which should otherwise be empty -- and type

    jar -xvf JSkyCalc.jar
That will pull all the files out of the archive (in place, which is why you want to do this in an otherwise empty directory!). Then edit the file skycalcsites.dat according to the instructions you'll find there. (If you happen to mess up the editing, copy the skycalcsites.orig file to skycalcsites.dat and start again. Don't edit skycalcsites.orig.)

You may be able to reconstruct the executable jar file by typing

jar -cvmf myManifest.mf JSkyCalc.jar .
-- don't forget the final "."! -- at least on a Unix-ish system. This might require the Java Developer's Kit, but it probably doesn't.

Alternatively, you can set your CLASSPATH environment variable to point at the directory you unpacked into (e.g., /home/thorstensen/java/JSkyCalc). Under the Linux bash shell, you set the CLASSPATH like this:

    export CLASSPATH
    echo $CLASSPATH    (this repeats it back so you can check it).
Environment variables are usually twiddled in your startup files somewhere -- something like .bash_profile, or .cshrc -- so you can make the change permanent by editing the appropriate file.

I don't "do" Windows, but I gather from the Windows documentation that environment variables can be edited using the System tool, under the Advanced tab.

Once the jar file has been unpacked and the CLASSPATH has been set, you can start the program by typing

    java JSkyCalc
Of course, most users will want to put it on a taskbar of some sort, depending on their system.

The jar file does not include the java source code -- this keeps the file small and reduces the startup overhead for webstart. If you do need the source code, please contact me.

Thanks to Susan Schwarz of Dartmouth's Peter Kiewit Computing Center for helping prepare JSkyCalc for distribution, and Jan Largent of the Department of Physics and Astronomy for posting it.

Release notes: