> The display shows a free-running simulation of Jupiter and 63 of its moons. For convenience, I just plot the X/Y coordinates of each moon in the ecliptic plane. The ephemerides come from the HORIZONS server that NASA operates, at a specified date and time. The J90 just dumps a new frame whenever the Teensy has pulled the previous one, so with a teensy (ha!) bit of calibration on the micro controller side, it would be pretty easy to have the frames dumped in ‘real time’, which, knowing the starting time and date, would allow you to not-at-all-easily infer the current time by looking at the positions of Jupiter’s moons.
Someone finally came up with a time system more difficult for people to use than Star Trek's stardates.