Talk:Galilean moons

Galilean moons
I hope noone minds that I've moved this to "Galilean moons", in the plural, because there is really no such thing as a Galilean moon and the four only have in common their discovery in a group. I know this is not the usual singular convention, but consider usage; Google gives 28x the number of hits for the plural.--Pharos 00:09, 11 Mar 2005 (UTC)

Is there any evidence that anyone has ever actually managed to see even Callisto as separate from Jupiter with the naked eye? I suspect not. RandomCritic 17:22, 10 February 2006 (UTC)


 * The hard part is not the separation, the system is enormous the hard part is their relative dimmness and by far telling them from background stars. I'm pretty certain that at least Gamymede is regularly seen, but is confused for a background star, as it is much farther than most people would expect. 88.100.176.55 (talk) 06:55, 8 October 2023 (UTC)

Somewhere in the last forty years of "Scientific American" (and yes, I realize that that's not a solid citation) there was an article about what constitutes a "scientific discovery". The thrust of the article was that to obtain proper scientific credit for a discovery, it was not enough to make the discovery per se, it was also essential to infer the importance of that discovery. It gave as one example that there exist "Indian" (as in Native Americans) drawings showing that they were able to observe the moons of Jupiter but attached no significance to them. I realize that this is all very vague. Old_Wombat (talk) 12:46, 28 June 2011 (UTC)

Shouldn't the history behind the discovery of the moons come later in the article? Probably, the list of moons should come earlier.

I have an issue with this part of the article - 'whether this was actually achieved by the Chaldeans remains a matter of speculation'. Since the word 'Chaldeans' leads to a disambiguation page, it could do with clarifying. Unfortunately I know nothing about the subject, and many of the potential meanings could be the correct one. Hopefully one of you knowledgable people will be abl;e to clear this up.

Hi Rayyan Melazhikam (talk) 16:55, 5 November 2019 (UTC)
 * As far as order, Discovery usually comes first, its honestly just preference though, no right or wrong answers, would have to do a talk page poll, or an rfc to get a real idea of consensus, but who knows maybe its in a manual of style. I'll check into it. I'm actually curious to know now. MaximusEditor (talk) 06:27, 2 October 2020 (UTC)

Pre-Galilean observations
While the Gan De connection, dubious as it is, at least has a real astronomical observation behind it, the "Horus" and "Marduk" conjectures do not appear to refer to astronomy at all - the citation given is totally inadequate - and don't belong in this article. So I'm deleting them. RandomCritic 20:14, 30 October 2006 (UTC)

There are some interesting notes on the possibility of naked eye observations of the Galilean moons in an archived Sky & Telescope article. Spaceman13 21:56, 9 May 2007 (UTC)

Hodierna names
I'm having some trouble with these. For one thing it's not clear where they actually appear -- I assume the Ephemerides, but I can't find this securely stated anywhere. For another, it's claimed that the names are for the "four Medici brothers" -- but which brothers? The names given are Principharus, Victipharus, Cosmipharus and Ferdinandipharus. But Cosimo II's brothers were Francesco, Carlo, and Lorenzo -- no Ferdinand among them; and his sons were Ferdinando II, Giancarlo, Matteo and Leopoldo -- without a Cosimo. Ferdinando II had a son Cosimo (III) who would have been a child at the time of the publication of the Ephemerides. And who do Principharus and Victipharus refer to? My best guess at this time is that Principharus stands for the late Medici ruler at the time Hodierna was writing, Cosimo II; Ferdinandipharus for his son, Ferdinando II; Cosmipharus for Ferdinando's son, Cosimo III; and Victipharus (some web sources have Victripharus, I'm not sure which is correct) for Ferdinando's wife, Vittoria della Rovere. But that's all guesswork. If anyone has access to Hodierna's Ephemerides, perhaps they could see if it contains an explanation? RandomCritic 10:51, 31 October 2006 (UTC)

Visible with the naked eye?
The following sentences seem to be contradictory: "All four Galilean moons can, in principle, be sighted without a telescope." "Other than the Moon, Ganymede is the only planetary satellite that can be seen by the naked eye, but still can only be seen in good conditions." So which is it? Colin M. 11:55, 23 May 2007 (UTC)

Merge Medician stars
Support:


 * Of course, Medician stars should be merged into this article, as proposed in August 2007. Wikipedia cannot have 2 articles on the identical topic. Finell (Talk) 18:10, 28 October 2007 (UTC)
 * OK, the merge is done.--Pharos 17:23, 31 October 2007 (UTC)

Further work needed
Good work, and fast! To complete the merger, however, the subsection "Galileo" "Dedication" and the "Name" section s should be harmonized (there are fact conflicts) and duplication eliminated consolidated. Also, the facts and references should be harmonized with the relevant parts of Moons of Jupiter. Finell (Talk) 20:27, 31 October 2007 (UTC)
 * Yeah, and we should also explain the difference in dates of the discovery between the pre-merge version, "January 7, 1610", and the version from Medician stars, "December of 1609 or January of 1610", (which I went with because that version was obviously researched more carefully). If I recall correctly Jan. 7 may be one of a couple of exact dates that it could have been.  This requires further reading to clarify.--Pharos 23:11, 31 October 2007 (UTC)
 * I did some editing and reorganizing, but did not consolidate the two sections. I don't have the book at hand, but any citations that are to Helden's introduction to Sidereus Nuncius should specifically cite the introduction in the footnotes to correctly attribute authorship. Finell (Talk) 01:21, 1 November 2007 (UTC)

Galileo Discovery Dates
Callisto (only one with discovery date reference), Io, and Europa are listed as discovered on January 7, 1610. But Ganymede is listed as discovered on January 11, 1610? Should all four Galilean moons be listed as discovered on the same date? Do we have a reference that shows Ganymede was truly discovered last, even though Callisto orbits further out and Io switched sides every day further confusing Galileo? -- Kheider 19:02, 8 November 2007 (UTC)
 * All four are visible to the unaided eye and were probably seen and mistaken for stars for thousands of years. Much the same happened to Uranus. — Preceding unsigned comment added by 196.203.109.25 (talk) 11:42, 26 March 2015 (UTC)

Longitude: Jupiter's moons help calculate GMT, not local time
The article states that "The times of the eclipses of the moons could be precisely calculated in advance, and compared with local observations on land or on ship to determine the local time and hence longitude." I think this sentence can be understood multiple ways. I initially thought it meant that the moons of Jupiter could help determine local time. However, I doubt that is what it should mean. More likely, comparing the observed moons of Jupiter to pre-calculated tables would provide universal time (GMT) and other observations (such as Sun's Zenith, moon rise, etc) would determine local solar time. The differences between these times then provides longitude. If my understanding is correct, I think the sentence should be expanded and clarified. Else if my understanding is incorrect, it should be clarified anyway. :) Alexgenaud (talk) 14:45, 7 September 2018 (UTC)

Interior structure
There are some images in the article which show the interior sturcture of the moons. However, these are rather speculative. There is also no data on the different densities/compositions of the data which makes the images meaningless. There is no evidence to prove these structures are correct? How were they obtained? Polyamorph (talk) 10:57, 14 January 2008 (UTC)


 * Ok, more detail is provided on the interior structure in the individual articles relating to each moon. However, the images are meaningless on this page since the layers aren't labelled or explained.  Considering this is already done in the individual moon pages, the interior structure images are superflous on this page and I will therefore remove them.  Polyamorph (talk) 12:56, 14 January 2008 (UTC)


 * The models of the interiors are provided by CalTec's Jet Propulsion Laboratory. All the background information is directly accessible by clicking the images. All models of the interior of planets, including our own planet, are speculative - that is implied in the word 'model'. These are the latest authoritative models. The value of showing them in a comparative table is that it is possible to see how the interiors may vary with distance from the tidal heating effects of Jupiter. Io, in the centre, has no ice and a hot interior. The ice proportion increases as you move out. Only Callisto, the outermost one, remained so cold and solid that internal differentiation did not occur. This could all be left to individual articles - but then so could everything else about these four moons. We could, by such logic, delete the entire article. —Preceding unsigned comment added by 82.71.43.37 (talk) 20:35, 24 May 2010 (UTC)


 * The models are not explained in this specific article, which was my point. I disagree that the word 'model' implies speculation, one must strive to make the most accurate models possible based not on speculation but on verifiable and unambiguous experimental information. But that is for another discussion. If you feel that the models are useful to show how the interiors vary due to tidal heating etc then I agree that this is a very useful comparison. However, this really should be mentioned in the article prose with reference to the images, otherwise the reader doesn't know what comparison they are making. Which was my main point all along, without proper explanation the images are meaningless to the reader. Polyamorph (talk) 13:00, 28 June 2011 (UTC)

Ganymede
There was a reference by the late Patrick Moore

"Ganymede, Prince of Troy".AT Kunene (talk) 10:09, 22 May 2013 (UTC)
 * Is this notable? Do you have reliable sources to cite? if so add it in and be bold. MaximusEditor (talk) 06:28, 2 October 2020 (UTC)

Contradiction
The sections "Dedication to the Medicis" and "Name" contradict each other. Tad Lincoln (talk) 02:16, 2 April 2014 (UTC)
 * One says Cosimo made the suggestion. One says that Cosimo's secretary made the suggestion. — Preceding unsigned comment added by 92.26.0.234 (talk) 14:47, 22 September 2014 (UTC)

Archaic data
Our articles use refs that in turn cite Voyager and even pre-Voyager data. Especially for the physical parameters, we should be using Galileo data, shouldn't we? — kwami (talk) 23:46, 11 April 2014 (UTC)

Arcmin vs. arcsec
I changed something that said minutes of arc to read as seconds of arc and it was reverted. If it is indeed minutes then the citation on reference 44 should be changed to read arc min as well. TeigeRyan (talk) 23:42, 6 October 2014 (UTC)
 * Maybe I'm missing something, but the footnote says "631 arcsec = 10 arcmin". --JorisvS (talk) 08:16, 7 October 2014 (UTC)
 * I do not know if it was changed or if I was unclear, but it certainly seems clear now, so I am good. Thank you.TeigeRyan (talk) 03:30, 22 October 2014 (UTC)
 * It was already that way when you changed it and, looking through the edit history, it has been so for years. --JorisvS (talk) 10:33, 22 October 2014 (UTC)

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Self-contradiction
The second paragraph contradicts the paragraph entitled "Visibility".
 * The first paragraph does the same thing. — Preceding unsigned comment added by 77.93.16.228 (talk) 12:36, 3 September 2018 (UTC)
 * There are more contradictions in the article, along the same lines. — Preceding unsigned comment added by 77.93.16.228 (talk) 12:41, 3 September 2018 (UTC)
 * As the four brightest moons are visible to the unaided eye, they were probably seen in pre-historic times and in early historical times, before the Chinese observation of one of them. — Preceding unsigned comment added by 161.142.105.64 (talk) 13:39, 4 September 2018 (UTC)
 * that is highly unlikely Thony C. (talk) 05:11, 5 September 2018 (UTC)

first seen when? first and second paragraphs contradict
1st para: They were first seen by Galileo Galilei in January 1610. 2nd paragraph: The Galilean moons were observed in either 1609 or 1610 when Galileo made improvements to his telescope. I suggest merging them to fit the 2nd paragraph. As an aside, the article should not mention the discovery in 2 separate place in the lead. I intend to rearrange the lead to have one paragraph on their properties, one on their discovery, and one on their names. Adpete (talk) 00:31, 25 March 2019 (UTC)


 * Also something about Simon Marius' (probable) independent discovery should be in the "Discovery" section. Adpete (talk) 00:33, 25 March 2019 (UTC)

Orbit animation
In "Latest revision as of 12:46, 11 July 2019", Drwonmug put some discussion into the main article. It looks like it belongs here in Talk, so I reverted that change. This was the text:

"This has been widely cited -- cf eg

https://www.explainxkcd.com/wiki/index.php/1300:_Galilean_Moons

but I believe it is an oversimplification and is in fact false; at least, it deserves a reference:

According to J\"urgen Moser, Stable and random motions in dynamical systems, [Hermann Weyl lectures (1973), the Institute for Advanced Study Annals of Mathematics studies 77 Ch I p 7]:

"Between three of the Galilean moons of Jupiter one has a relation  \omega_I - 3\omega_II + 2\omega_III \sim 0 to a high degree of accuracy..."

(where \omega denotes the orbital frequency). The current wikipedia article asserts something like \omega_I \sim 2\omega_II \sim 4\omega_III (though I'm not sure of the indexing, ie of which moon is labelled I,II,III etc). This is incompatible with Moser's assertion, which is {\bf extremely} authoritative."

He later added in this talk page,

"added by drw later on 12 July in an attempt to clarify things: apologies for not being more familiar with Wikipedia practice:

Thanks for moving this here! I don't try to edit things very often and didn't intend to step on the article itself, I apologize; I meant to put my comment on the talk page but couldn't find it; or, more precisely, thought that was what I was doing.

I have a copy of Moser's book and would be happy to scan a couple of pages to .pdf if that would help. I'm afraid that actually

(1 - 3/2 + 4/2) = 1 + 1/2 = 3/2 is NOT equal to zero.

BTW I like xkcd a lot and think he would be interested in this discussion but don't want to muddy the waters.

Thanks for taking this seriously! signed as best I know how by DRWONMUG

— Preceding unsigned comment added by Drwonmug (talk • contribs) 13:44, 12 July 2019 (UTC)"

That book is in JSTOR, but I can't get to it myself. I can find another source in a lot of places: Peale, Stanton & Hoi Lee, Man. (2002). A Primordial Origin of the Laplace Relation Among the Galilean Satellites. Science (New York, N.Y.). 298. 593-7. 10.1126/science.1076557. One source is https://www.researchgate.net/publication/11075719_A_Primordial_Origin_of_the_Laplace_Relation_Among_the_Galilean_Satellites

It gives the same equation as Moser but using different notation, stating "numbered consecutively for Io, Europa, and Ganymede, respectively .... leading to n1 − 3n2 + 2n3 = 0, where ni = {λ dot}i are the mean angular velocities with the dot indicating time differentiation."

"Orbital frequency" and "angular speed" are synonyms. Lowercase omega is the usual character used for angular speed.

But mean angular velocity / mean angular speed is not the same as orbital period. For a circular orbit, orbital_velocity = 2*pi / orbital_period. (I don't know how to do the fancy-pants math markup, and I'm not inclined to look it up in this simple case.) I think that, because it's MEAN angular velocity, we can consider the orbits as if they were circular. So

2*pi / period_Io - 3*2*pi / period_Europa + 2*2*pi / period_Ganymede = 0

The proposed orbital-period resonance would have the periods 1:2:4. To make the formula shorter, call period_Io = T, so if the proposed orbital-period resonance holds, 2 * T = period_Europa and 4 * T = period_Ganymede. Does that satisfy the equation?

2*pi / T - 3*2*pi / (2*T) + 2*2*pi / (4*T) = 0

Divide both sides by 2 * pi.

1 / T - 3 / (2*T) + 2 / (4*T) = 0

Multiply both sides by T.

1 - 3/2 + 2/4 = 0

So the stated resonance orbital periods do fit the equations from Moser and Peale + Hoi Lee. (Edit note: thanks to DRWONMUG for pointing out that my original version was incorrect. I had typoed 4/2 instead of 2/4.  While I'm here, I've also uncompressed the steps to make it clearer.)  So the equation from Moser, or from Peale + Hoi Lee, for mean orbital velocity implies the 4:2:1 orbital period resonance.

Tim McDaniel (talk) 23:29, 11 July 2019 (UTC)

Thanks from Drwonmug! I'm sorry about the confusion. I should maybe say that what really concerned me about this (and still does) is that one linear relation

\omega_I - 3\omega_II + 2\omega_III \sim 0

is not the same as two linear relations

2 * period_Io = period_Europa, 4 * period_Io = period_Ganymede

so I suspect there is some further physical fact lurking somewhere behind all this; but that is not something for Wikipedia to explain and I will shut up now.

But BTW Wikipedia has a very nice https://en.wikipedia.org/wiki/Orbital_resonance page which probably deserves to be linked somewhere in this article.

Thanks again! — Preceding unsigned comment added by Drwonmug (talk • contribs) 14:57, 14 July 2019 (UTC)

One scale for mass
Why not to use one scale for mass? Why two are 10^22 and two are 10^23? Why not to use single scale 10^21, 10^22 or 10^24 for all 4 entries in the table? Or better use SI prefixes - Yg (yottagrams). Elk Salmon (talk) 16:14, 12 December 2021 (UTC)

rape victims or lovers?
This article describes the namesakes of the Galilean moons as both "rape victims" of Zeus and as "lovers" of Zeus but these are contradictory terms. I am not a classical scholar, so which is the case? Nicole Sharp (talk) 18:32, 30 April 2023 (UTC)


 * Both are in fact true in the context of fables that are thousands of years old, but the two are not true in the context of the 21st century. I feel that very few people now would see "lovers of Zeus" and expect that this was rape. The reference in this article is a work in progress by me, and I'm trying to be accurate according to classicists. I also feel this really matters because the Galilaen moons are bubbling up in popular awareness due to increased scientific activity.
 * I wrote in the Talk page for the list of mythological rape victims:
 * All four moons are named after "lovers of Zeus" according to that article, but in fact these mythological humans (three female and one male) were all abducted and raped by Zeus. I will eventually change the Galilean moons article to more correctly describe the origin of the names, assuming my additions are factually accurate according to classicists.
 * There is some supporting information in the article Rape in Greek mythology, and plenty has been written by classicists on the topic of Western mythology and rape/coercion/unwanted pursuit/etc. For myself, I don't want to master this tricky topic, just to highlight a basic fact for modern people hearing the term "Galilean moons." There isn't any glossing over it, these are moons we are visiting in the 21st century and they are all named after rape victims. However it is also true that these moons got their names in a perfectly legitimate manner, and there are unpleasant sides to most of the myths associated with named astronomical objects.
 * Can you think of a better way to address this? If so, great.
 * Dan Shearer (talk) 22:46, 2 May 2023 (UTC)
 * Dan Shearer (talk) 22:46, 2 May 2023 (UTC)