V-3. Help (.HLP) Files
Help files (qualifier .HLP) for the CLEA Windows exercises are simply text files, which can be created and modified with a text editor, including the MS-DOS editor provided with Versions 5.0 and above (access MS-DOS and type EDIT). Text files can also be created with a word processor. (If you use a word processor, be sure that you generate your final output in straight ASCII text, not in the word processor’s internal format or formatted for a printer. Most word processors have an option to generate ASCII text. You may also need to eliminate page breaks. It may be cumbersome or difficult to edit existing text files with some word processors.)
We have provided the User Help menu item to accommodate specific instructions, information, etc. that the instructor may wish to impart to the students. To create a user help file, simply create a text file (we recommend a maximum of 72 characters per line), copy it to the working directory, and enter its name in the User Help File field on the options dialog. You can also use a text editor to modify the existing help screens or create replacements. V-4. Data (.DAT) Files
This exercise uses no data (.DAT) files.
V-5. Logout “Reminder” File
This (optional) file provides a mechanism for the instructor to supply customized messages to the students when they have finished the exercise. The contents of the (text) file identified in the Reminder File field on the options dialog are displayed whenever Quit is selected from the main menu. This display always concludes with the line Select OK to Quit Exercise, Cancel to Continue, and provides pushbuttons affording the appropriate choices. A reminder file can be any text file (create with a text editor), with the following restrictions: 1. The total message may not exceed 1023 characters.
2. A “line” (see next) may not exceed 255 characters.
3. Carriage return-line feed (CRLF) characters in the file will result in new lines in the output. However, additional new lines may appear because the output will wrap itself automatically. This wrapping depends on the video mode, and employs variable length characters, so the resulting line length is nearly impossible to predict. It is recommended that CRLF be used only to terminate paragraphs, which then become long lines subject to the length restriction above. Some experimentation may be required to achieve a message that displays as intended. We have provided a default reminder file REMINDER.JUP, which may be used as is, modified with a text editor, replaced, or simply deleted, if desired. If no reminder file is provided to the program, a short message (Do You Really Want to Quit This Exercise?) is displayed when Quit is selected.
VI. Astronomical Data, Models and Algorithms
Calculations of the positions of the Jovian moons with respect to the planet for this exercise employ the “Low Accuracy” method described by Meeus (1991). Although possibly not accurate enough for precision timings of eclipse and transit phenomena, the method is more than adequate for its use here. (It is interesting and educational to compare the displays from this program with Galilei (1610) for the dates therein.)
The Jupiter image, scaled and used for the title screen and all the views, was taken by Voyager. We apologize for its nonauthentic clarity (256 color versions) and gibbous phase (compared to Earth-based telescopic views).