When Jupiter is undergoing retrograde motion as seen from the Earth, would you expect the eclipses of Jupiter’s moons to occur several minutes early, several minutes late, or neither?
Can someone please explain?

I am a novice in astronomy, and I read a couple of articles on the retrograde motion. I understand it is an illusion. But how would I expect the eclipses of Jupiter's moon?


1 Answer 1


The fact that eclipses are either "early", "on time" or "late" only depend on the distance between Jupiter and the Earth. Since the speed of light is not infinite, a longer distance means a longer delay between the actual eclipse and the time it is observed from Earth.

For superior planets, retrograde motion occurs around opposition, at a time when the distance between the planet and the Earth is minimal. So you should expect eclipses to appear early during retrograde motion. But note that the early eclipses are not a consequence of retrograde motion: they are both consequences of keplerian motion.


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