Overview

This program computes the locations of the Galilean satellites of Jupiter for a user specified date and time.

Features

• You can specify a time and date to see how the moons appeared.
• You can specify an offset from UT so you can use your own local time.
• You can set a user defined "step time" in decimal hours and watch how the moons change their location. The step can be positive or negative!

Known Limitations

(shareware version)

• The program does not save the UTC or Step settings. These are reset each time the program starts.
• Displays "binocular" or normal view. West is to the left of the display.
• Jupiter is not to scale.
• When using the Step button, the displayed date and time does not update although the internal values for the date and time of the displayed configuration does.

Future Plans

(for the registered version only)

• Save State feature, to save user settings.
• East-West display flip for binocular (normal) and telescope view.
• Floating legend to identify the moons.
• Display Jupiter to scale.
• Update the displayed date and time when using the step option.
• Auto-step option to allow the program to step from a specified date through a range of days at a user specified interval showing the moons at each step point.

The Main Screen

Installation

This program only runs on the PalmOS version 2 or higher. It does not work on earlier versions of PalmOS.

J-Moons!(10k) requires the MathLib library (54k) and the CASLrt runtime (39k) to be installed before it can be used. This makes the total memory requirements for J-Moons! 103k. Although this is a significant amount of memory, MathLib and CASLrt can be shared by other programs. If you have programs that use MathLib (MathPad for example) or CASLrt you're minimizing the duplication of capabilities that takes place in alot of stand alone programs.

MathLib is a free shared library that can be used by any OS 2.0 Pilot program that needs IEEE 754 double precision math functions. It's distributed under the terms of the GNU General Public License, and is freely available with full source code and documentation at the MathLib Information web page at http://www.probe.net/~rhuebner/mathlib.html. It's not a part of the CASL runtime programs, and you're not paying anything for its use; a copy is simply included in this archive for your convenience.

WARNING! If you're currently using CASL version 1.0 programs, you should not download and install this program until CASL version 2 versions of your programs are available, unless of course, you no longer want those programs. CASL version 1 and version 2 programs CAN NOT co-exist.

To see which version of CASLrt you have, find the CASLrt Icon in your application display and select it. At the top of the screen, the version will be listed.

As the library of programs available that use MathLib and CASLrt grows, memory utilization on your pilot will be more efficient. The break even point for memory utilization with CASL programs that use MathLib is around 3 programs.

Before using the program, use the PalmPilot installation tool to install MathLib.prc, CASLrt_pro.prc and jmoons10.prc.

Operation

When you run the program, the current date and time for Greenwich will be used to show the positions of the moons around Jupiter.

To put in your correction to UT for local time, for example, Danville, VA is currently -5.0 hours from UT, select the field with UTC and put in the appropriate value for your location. Once you have the appropriate value in place, press the Go button to update the display.

You can change the date and time in the same manner as you change UTC. Enter the appropriate date and time and press the Go button.

To get the position of the Galilean moons at the current time (using the current setting of UTC) you can press the Now button.

Press the Step button to increment the selected time by the number of hours (in decimal) and draw a new representation of the moons. You can enter fractional hours in the field, for example, 1.5 represents 1 hour 30 minutes.

Other Screens

Computations Screen

The Computation Screen shows the various values of different variables computed to display the current positions of the moons. These values are named identically to the ones used by Jean Meeus in his book Astronomical Formulae for Calculators, 4th Edition.

• d - Number of days (including fractional days) since 1899 December 31 at 12h ET.
• V - Long period term in the motion of Jupiter.
• M - Mean anomaly of Earth.
• N - Mean anomaly of Jupiter.
• J - Difference between the mean heliocentric longitudes of Eart and Jupiter.
• A - Equation of Center of Earth.
• B - Equation of Center of Jupiter.
• K - J + A - B.
• u1 - u4 - Angle measured from the inferior conjunction with Jupiter.
• R - Radius vector of the Earth.
• r - Radius vector of Jupiter.
• x1,y1 - x4,y4 - Location of each moon with respect to Jupiter at the center (0,0) coordinates and measured in radii of Jupiter.

All angle values are degrees.

Help About Screen

Release History

• 28 November 1997 Initial release.

Registration

To register your copy of J-Moons! send $5.00 US to the address below.

Legal Notice

This software and documentation is copyrighted © 1997 by Marvin E. Wilborne III (mailto: wilborne@gamewood.net). This software is provided "as is" and without warranties. All liabilities expressed or implied are disclaimed. All rights reserved.

The registered J-Moons! software may not be distributed.

Contact Information

Address:

	Marvin E. Wilborne III
	124 Matthew Circle
	Danville, VA 24540

Web Address: http://www3.gamewood.net/mew3/pilot/

E-mail Address: wilborne@gamewood.net