1. Eclipses of Jupiter’s moons
Earth Io
Sun
Light from eclipse #1 travels this far

2. Eclipses of Jupiter’s moons
Light from the next eclipse has
to travel this much farther vE
Jupiter
Earth Io
Sun
vEt
Measured time between eclipses is
longer than actual time by the time
it takes light to travel this distance

3. 6 months later Sun Light from eclipse #1 travels this far Jupiter Io
Earth
Light from eclipse #1 travels this far

4. 6 months + later Measured time between eclipses is
Jupiter Io
Sun
Jupiter
Earth vE
vEt
Light from the next eclipse travels
a distance that is this much shorter
Measured time between eclipses is
shorter than actual time by the time
it takes light to travel this distance