It uses the low precision algorithm found in the book "Astronomical Algorithms" by Jean Meeus, published by Willman-Bell Inc. 1991.
Operation
When JupiterViewer is started is shows the positions of the moons at the
moment of startup. The big "blob" in the middle represents Jupiter and the
smaller numbered dots represent the four Galilean moons in orbit around
Jupiter. 1 is Io, 2 is Europa, 3 is Ganymede and 4 is Callisto. The small black
dots sometimes seen on Jupiter represents the shadows of the moons. When a moon is
in Jupiters shadow or behind Jupiter as seen from earth it isn't visible. The red oval sometimes visible on Jupiter represents the famous "great red spot" (GRS).
To see the position of the moons and GRS at the current time (according to your computers system clock) press the Now button.
To see the positions at any other time change the date shown in the input fields and press the Calculate button. If you entered an illegal date an error message will be shown in the status bar.
To step the time forward or backward by approximately 15 minutes, press one of the arrow buttons.
To see an animation over time of the movements of the moons, press the Movie button. To halt the animation press Calculate.
View
Jupiter with satellites is by default shown as seen from the northern
hemisphere in a pair of ordinary binoculars. This can be changed however with the
different options under the view menu.
Flip L/R mirrors the view like it is shown in some telescope designs with odd numbers of mirrors.
Flip T/B flips the view upside down so that it is seen as in an inverting astronomical telescope.
Print preview shows the view exactly as it should look like when printed on paper.
Top view shows the view from "above" the ecliptic.
Show LT determines if local time is shown or not. Show LT is set by default.
Show UTC determines if universal time is shown or not.
Show JDE determines if the Julian Day Number is shown or not.
To zoom in and out in the view, use the slider below the view.
Spiral Diagram
To see a spiral diagram first set the date to when you wish the diagram
should start, press Calculate and choose Diagram under the
view menu.
A dialog window with the diagram should show up. By default 10 days is shown in the diagram. UT dates are shown on the left and Julian day numbers on the right scale. To change the numbers of days shown in the diagram choose Configure under the Window menu.
To print the diagram choose Print.
The diagram can be mirrored by choosing Flip L/R under the dialog windows View menu.
Printing
To print the Jupiter view choose Print under the File menu.
You might want to change the Print setup first. Choose
Many colors if you have a color printer and can waste a lot of
black ink.
If you have a color printer but dont want to waste ink, choose Less
colors. If you only have a B/W printer or dont like colors you might
choose Black & white. Print preview under View should
show you what the print will look like.
The spiral diagram is printed with the Window-Print menu in it's dialog window.
Configure
Under this menu you can configure the longitude of the GRS (default is 73.0 deg.)
and also set the date with a Julian day number. Only JD between year 1600 and 2500 is allowed.
Note that all dates are shown as Gregorian calendar dates. The shift from the Julian
calendar to the Gregorian calendar did not happen at the same time in every country,
which may lead to some confusion regarding historical dates.
Look & Feel
Look and feel can be chosen from the list under the Look&feel menu.
If you choose a look & feel that doesn't exist in your environment nothing
will happen. Just choose another one or be content with the one you got
already...
License
This program is copyrighted by Jan Lindblom, but may be freely copied, used and
distributed by anyone as long as no fee (except maybe for media) is involved.
Change log
Version 1.1.2: Bug fix release. Fixed the JD input dialog. Rewrote parts of the code.
Version 1.1.1: Bug fix release. The month number in the spiral diagram wasn't right.
Version 1.1: Added shadows for moons and Jupiter. Added great red spot.
Added a configuration menu for GRS and the possibility to use JD as input.
Fixed a bug in the handling of dayligth savings time.
Version 1.0: First release, July 2000.
Bugs and suggestions
E-mail bug reports and suggestions to jv_bug_report@yahoo.com. Please
include all available information in your bug reports.