1. You might be right concerning the fact that with current telescopes we can see planets rotate. I honestly wouldn't know but I am willing to take your word for it.
Please do not forget that we are talking about the 17th century, and I do not think that the telescopes then, which were no better than cheap binoculars, would be capable of such a feast. — Hachem
Vagabond Spectre wrote: Parallax and resolution are not the same thing, and parallax has little or nothing to do with this experiment. Parallax is the apparent motion of objects due to changing perspectives of observation, which unless you can correct me has nothing to do with visible light after the emergence of Jupiter's moon following an eclipse. Resolution is not an issue either, as we do not need to see Jupiter's moon with any high degree of detail whatsoever, we just need to see when the light from it becomes visible after it's emergence from behind Jupiter.
Concerning the first part of this quote, this is as far as I can see an argument in my favor. We are capable of seeing objects as they really are, therefore with no delay. You reaffirm the idea by stating "bigger telescopes mean more resolution" which seems to indicate that we see distant objects as they are. I am curious as to how you reconcile the idea that telescopes give an accurate image of reality with the principle that it takes time for light to reach us (on that we agree), and that therefore the images we see represent an image of a moment in the past. All I am saying is that we are not looking at the past but at the world as it is now, and that is the puzzle we have to solve. — Hachem
2: It means that there is a continuous flow of photons, and the "snap-shot" effect you're trying to describe is a mere consequence of us actually taking snap-shots. No such effect has been demonstrated to exist or to be the cause for the variations in eclipse duration of Jupiter's moon. — VagabondSpectre
That means in the case of eclipses or reappearance of moons from behind Jupiter that greater distances would make it more difficult for an observer to pinpoint the moment of disappearance or reappearance. — Hachem
The point of using Io was that the reappearance is obvious and effectively instantaneous. But anyhow, given that the relevant time difference between eclipses were in the order of minutes, a second or two would make no difference to the calculation. — Banno
I am afraid you are wrong. Romer's calculations were based on the average of observations made over 10 years! So it was a matter or seconds, or even less! — Hachem
In fact the maximum delay was sixteen and a half minutes later than would have been expected if the speed of light were infinite. — Banno
The question is whether the differences in the times of eclipse and reappearance of the moon cannot be interpreted differently, without involving the idea that it takes time for light to travel through space. We all know that when looking through the telescope at a planet like Jupiter, we do not see it rotating about its axis, or orbiting the sun. We get each time a snapshot of a frozen moment in time, and the changes to the images we receive occur in jumps without any intermediate states. This is understood as the effect of parallax, or more simply resolution. Because of the distance two points separated by relatively large distances will appear to our perception as one, and it takes time before we notice the difference between one position and another. — Hachem
Let us say you are looking at Jupiter and you see the moon disappearing or appearing. In this case, it would be like looking at a large object slowly being drawn behind a curtain, or from behind a curtain — Hachem
Again, differences of a second or two would have negligible impact on a demonstration involving minutes. Issues of resolution or parallax would not result in such large delays. — Banno
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