Calculate the "current" date and time at Greenwich (for the time the satellite positions are wanted). Look up the corresponding Julian Date (see Appendix 11 in the text), and add the decimal fraction of a day, as necessary. Subtract the date for which the data above are correct (JD 2445700.0). This gives D, the number of days (and fractional days) since the starting date.
     For each satellite, divide D by the synodic period, to get the number of times that the satellite has gone around Jupiter since the starting date, then multiply the FRACTIONAL part of the result by 360 degrees, and add the starting angle. This gives the current angular position, relative to Jupiter. (You only use the fractional part of the result because any whole number of revolutions simply returns it to the starting angle.)
     For each satellite, plot the position on a polar coordinate graph, and project the position to the line of the night sky, OR take the sine of the current angle and multiply by the semi-major axis of its orbit, to find its position relative to Jupiter (the +/- result corresponds to E/W positions, relative to Jupiter's position; whether + is E and - is W, or vice-versa, was left off the original version of this page; the answer to this question will be posted in a later revision).