Astronomy: Eclipse of Jovian satellites/speed of light

Mar 2017
I'm attempting to replicate the Ole Roemer method of determining the speed of light using the eclipse of Europa as a cosmological clock. This requires that I sum the period of Europa to predict the time of the eclipse.

When I note the predicted time of the eclipse, I see there is a 4 minute deviation of this time from the orbital period of europa.

I do not see how the eccentricity or the inclination of the satellites can effect when the satellite enters the shadow. The rotation of the shadow of Jupiter does not seem to be significant enough to cause the delay. Does anyone have any suggestions for what might be causing the additional delay?


PHF Helper
Jun 2010
Morristown, NJ USA
Without seeing your work, its impossible to know what your source of error is. I assume what you are saying is that you expect Europa to be early or late by plus or minus 8 minutes over the course of a year, and are getting 4 minutes instead?