As Hans Lipperperhey had made a decent telescope albeit worse telescope before Galileo, source, would he have been able to theoretically view the moons of Jupiter before Galileo if he had looked?
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$\begingroup$ What does it mean ? It seems hat Hans Lipperperhey has no interest in astronomy. So the issue is purely "alternative history". $\endgroup$– Mauro ALLEGRANZAAug 22, 2018 at 16:21
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1$\begingroup$ @MauroALLEGRANZA I think his question is simply whether existing technology may have allowed other "non-published" researchers to see the moons. $\endgroup$– Carl WitthoftAug 22, 2018 at 18:16
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$\begingroup$ There is this anecdote I heard once. (Sorry, I remember very little of it.) A sheep herder in the remote steppes of Russia told that "one star swallowed the other star". The larger star was then identified as Jupiter. Had he seen one of the moons with his naked eye? $\endgroup$– Gerald EdgarMay 15, 2020 at 10:38
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Given that it's reasonably easy to see the 4 major moons with a 6 to 8- power binoculars, (you can find hundreds of discussions of planet-gazing with binocs online) it is quite reasonable to suppose that a patient, skilled observer with a 3 or 4 X telescope could have observed these moons.
Keep in mind that Lipperperhey, or users of his 'scope, would have had not only to see the moons, but make enough observations to recognize that they are orbiting Jupiter rather than being other (perhaps even stellar) sky objects.
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1$\begingroup$ 1. Modern binoculars are by far superior to 17 century telescopes of the same magnification. 2. Magnification is not the main parameter which allows you to see the things in the sky. $\endgroup$ Aug 22, 2018 at 13:38
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$\begingroup$ @AlexandreEremenko true, but so far as I've been able to determine, those early scopes had excellent, if spherical, figures, so aberration was not a concern. Ditto for things like AR coatings, which aren't a serious concern for astronomical viewing in a nice dark environment. Similarly, the entrance aperture for H.L.'s scope is compatible with consumer binocs, so light collection is sufficient. $\endgroup$ Aug 22, 2018 at 13:46
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$\begingroup$ Doubtful. With Lippershey's 3x spyglass, Ganymede would be at most just 15' from the much brighter Jupiter. That is considered to be the limit of human acuity. So it might just about be technically possible but not with 1600s lenses. Even with Galilean telescopes, Saturn's massive rings were seen as blobs on each side. $\endgroup$ Sep 11, 2019 at 7:57