Jupiterium creates a simulation of Jupiter and its Galilean satellites as viewed from Earth through a small telescope. On-screen dimensions are accurate to the nearest pixel, and positions of the moons are accurate to a minute or two of time. [In the present form of this program, actual eclipses of the moons (i.e., by Jupiter's shadow) are not shown, only approximated by occultations (by the planet's disk).] Transits are distinguished from occultations in that a moon is shown in contrast against Jupiter's disk when in transit and not shown when occulted.
"Jupiterium" is for Macs without a floating-point coprocessor (6888x chip) and "Jupiterium881" is for those with.
You'll first be prompted for information related to your time zone and to choose whether the view should be set to correspond to that produced by an inverting, a reversing, or a terrestrial (spotting) telescope.
You'll then be prompted to choose one of three display modes:
-The REAL-TIME mode displays the configuration of the satellites at the current time as read from your Mac's internal clock; you'll choose whether this mode updates in real time at intervals of 5 seconds or in accelerated time in increments of 30 minutes at intervals of 5 seconds. Use this mode to check the moons' configuration and identification at the beginning of an evening's observing and to anticipate interesting events later in the evening, such as transits, occultations/eclipses, and juxtapositions.
-The OPTIONAL-TIME mode displays a static configuration corresponding to a time and date specified by you.
-The ORRERY (look it up!) mode is an animation that starts at the current time and advances in 30-minute increments as fast as the code is executed; equivalent speed will depend on the particulars of your machine's hardware. [I'd appreciate feedback on how it looks on a 33-Mhz 030/882 machine. I imagine it *cranks*!] Use this mode to appreciate the relative sizes of the four orbits and the relative periods and speeds of the moons. Because the time display updates with the positions of the moons, this mode may also be used to explore the near future to note the time and date of interesting configurations to facilitate observing them with your telescope.
To end the current display you must hold down the mouse button until you're returned to the top of the prompt sequence, where you'll be given the choice of re-running or quitting. Since this will happen only at the start of an update cycle (except in optional-time mode) you may have to wait up to 10 seconds until quit occurs (see next paragraph)
Jupiterium was written with the Macintosh Pascal 2.0 interpreter and compiled as a standalone application with Lightspeed Pascal 2.0. Jupiterium881 was compiled with the compiler instructed to produce 6888x code. The computational methods in this program are those given in Jean Meeus, "Astronomical Formulae for Calculators", 4/e, Willmann-Bell, Richmond, VA, 1988. Aside from that inspiration, the program is of my own design, written as the first project in my effort to teach myself programming. It is, in fact, my first program beyond the textbook exercises and their variations. In this primitive form, the program is conspicuously un-Mac-like in its interface, aside from the Quickdraw-generated graphic display. As I learn more about the specifics of Mac programming--grafPorts, menus, dialog boxes, and the like--I will release more sophisticated versions. But as an amateur astronomer as well as a novice recreational programmer, I am pleased with this interim accomplishment, so I am uploading it for your enjoyment. It may be distributed freely.
If you'd like to have a commented listing of the source code, which executes under both Macintosh Pascal 2.0 and Lightspeed Pascal 2.0, send me a formatted disk (first class, not book rate, as my address will change in May) and a POSTPAID RETURN MAILER.
