Sidereal or Synodic period

[TobyOnGithub]

Me and students are using Stellarium to make screenshots (same FoV) of Jupiter and its moons. We then measure the pixel distance of a given moon (fx Io) relative to the center of Jupiter. Fitting a sine-curve to the data will provide a period of the moon. Question: is it the synodic or sidereal period of the moon we measure?

[gzotti]

"You and students..." If you are the tutor, shouldn't you know the answer? Given the history of discoveries, I just mention Ole Römer and what he had to say about the observed periods.

[TobyOnGithub]

Sorry, but I tried to look it up. No luck. Conflicting answers. I do not know the answer. That's why I am asking for help.