# Talk:Amalthea (moon)

Why is it so hard to get at the facts?

JPL (the one used here): 2.07±0.45 E+18 kg (private communication of constants used in the JUP230 ephemeris, 2003)
JPL/NASA: 7.2E21 kg (obviously wrong)
JPL/NASA Galileo: 7.17E18 kg (undated)
Results from the Galileo Energetic Particle Detector During the Amalthea Encounter of November 5th, 2002: 7.17E18 (dated December 9, 2003; possibly pre-encounter value)
USGS: 7.17E18 (last updated May 11, 2004)
Urhixidur 23:30, 2005 May 13 (UTC)

Not wanting to tread on the article editor's toes, I'll list a few issues here:

Per WP:MoS#Article_titles, bold face should only be used for the first appearance of the title (or synonyms). The presence of so many amalthea's in the text seems distracting to me. Could it be cleaned up?
"the porous water ice" doesn't need a "the".
"mean motion resonances" may be unfamiliar to most readers. A brief explanation would likely help.
Mixing "color" and "colour" on the same page. (C.f. WP:MoS#National_varieties_of_English.)
tidally locked should be linked.
Thanks. — RJH (talk) 19:53, 20 May 2007 (UTC)

I fixed the issues above. Thanks for comments. Ruslik 08:20, 21 May 2007 (UTC)

I'm placing this article on hold for now. It's well-written, nicely cited, and approachable to non-experts. The only thing which stops me from passing this article is the extremely short lead. WP:LEAD states the opening paragraph "should be capable of standing alone as a concise overview of the article, establishing context, summarizing the most important points, explaining why the subject is interesting or notable, and briefly describing its notable controversies, if there are any." and goes on to recommend up to four paragraphs in the lead. This article has just one paragraph, only 80 words long, which certainly does not summarize the contents of the entire article. Aside from this concern, the rest of the article seems to satisfy all the requirements. Firsfron of Ronchester 03:50, 25 May 2007 (UTC)

Thanks for a review. I rewrote the leading section. Please, read it with attention to find typos that I may have missed.Ruslik 08:40, 25 May 2007 (UTC)
Excellent work. I don't see any typos, and the lead is long enough. Everything seems in order. Good job! Firsfron of Ronchester 02:26, 26 May 2007 (UTC)
Thanks again! If you have time you can read Rings_of_Jupiter article which I listed for a peer review. Ruslik 13:05, 26 May 2007 (UTC)

A couple of details which would be good to sort out. In the article one finds the following statements:

These values of inclination and eccentricity are unusual for an inner satellite... — In what way?
In the way that they are not zeros. Ruslik 06:49, 24 July 2007 (UTC)
Amalthea is irregularly shaped, with dimensions of 250x146x128 km — are these the actual maximum dimensions, or the best ellipsoid approximation?
Ellipsolidal approximation, see Thomas et.al 1998. Ruslik 06:49, 24 July 2007 (UTC)
Deuar 13:28, 23 July 2007 (UTC)

The 'citations' for this section simply read "Calculated from known distances, magnitudes, etc.". A source is given for the distances and magnitudes, but the nature of the "calculation" is not explained. How do we know this information is accurate, and not based on bad mathematics by a random Wikipedian? This section is very interesting but please provide better sources, or at least explain the calculation so it can be verified. Rubble pile 18:37, 5 September 2007 (UTC)

I don't understand why you removed those two refereneces. If you thought that explanaition was not enough, you could simply put 'fact' tag without removing anything. By removing them you left a hanging ref in the reflist. As to calculations they are very simple. Angular size is geometrical size of the object divided by distance to it. The brightnesses scale as inverse square law. The difference in visual magnitudes is m1-m2=−log2.512(I1/I2), where I1 and I2 are brightnesses. The last number 8500 is 922. You wrote "How do we know this information is accurate, and not based on bad mathematics by a random Wikipedian?", however if find an internet link "How do we know this information is accurate, and not based on bad mathematics by a random internet blogger?". These numbers are difficult to find in reliable sources, because they don't have any scientific value and are calculated for illustative purposes only. If you think that the numbers are wrong, please, check them and insert correct ones. Ruslik 08:48, 6 September 2007 (UTC)
I wasn't saying they were wrong, I was saying you should describe the calculation within the citation so people can check it, rather than simply ask them to trust you. When doing so, you should provide a source for the statement "visual magnitudes is m1-m2=−log2.512(I1/I2), where I1 and I2 are brightnesses", because otherwise, how does the reader know this is accurate? Citing random internet bloggers is of course against policy, so that's not the issue. This is a very interesting section, but it needs to be properly verifiable. Rubble pile 14:42, 6 September 2007 (UTC)
I would think a wikilink to visual magnitude is all that is needed rather than a full-blown reference. I don't think this sort of note needs to belabour all the gory details such as which number was multiplied by which. Something like "calculated from geometry as given in the Amalthea and Jupiter articles, and using visual magnitude as m1-m2=−log2.512(I1/I2)" should be enough. As an aside, like Ruslik, I also find that it is almost impossible to find trustworthy references for many "popular interest" quantities because they are not usually scientifically notable, and one should just calculate them. I's not rocket science to multiply a couple of numbers on a calculator. Deuar 22:57, 6 September 2007 (UTC)
That would be OK, especially if we could link to the relevant section of visual magnitude, rather than the page as a whole (which is rather alarming for the layman). But what about the claim that Jupiter would look 46 degrees wide from Amalthea - how do we know that? (Currently the 'source' provided is a painting, which is very pretty, but provides no evidence for the given figure.) I'm sorry if I seem to be banging on about this, but it's important - I agree that it's OK to calculate these figures, but we should show how they were calculated. What seems obvious to some editors is not obvious to others. Rubble pile 02:12, 7 September 2007 (UTC)
I added a wikilink to the visual magnitude in the ref 16. As to 46 degrees ? But you know radius of Jupiter Rj=71,500 km and radius of the orbit Ro=181,400 km and the angle is 2*arcsin(Rj/Ro) ≈ 2*Rj/Ro. So I opened calculator and obtained 46.4 degrees. However if you don't agree with my arguments that such calculations are too trivial, you can expand the explanation given in the article youself. It will be you contribution to this article, especially taking into account that you have edited it before.  I reverted you edits primarely because you put too many (six!) 'fact' tags into two paragraphs even after 8500 number, which was obviously 92 squared. Ruslik 07:30, 7 September 2007 (UTC)
OK, I'm happy now! And yes, I will add the information in myself. I have nothing but respect for your skills, and I'm just trying to make the point that many people are knowledgeable about the solar system but not about mathematics so something like "2*arcsin(Rj/Ro) ≈ 2*Rj/Ro" is not trivial or obvious! I'm sorry if I came across as rude, but I just wanted to know where the information came from. Thanks for your help. Rubble pile 12:35, 7 September 2007 (UTC)
If in the process you get any questions I am ready to answer. Ruslik 13:22, 7 September 2007 (UTC)
Hi, I've added the harder calculations to the footnotes, and I'm content. However, I'd be grateful if you guys could proof-read them to ensure that I haven't misunderstood anything. Rubble pile 17:10, 7 September 2007 (UTC)
You know, upon second thought, I now think this calculation is not as trivial conceptually as it first seemed. In particular, the plot thickens because Jupiter's radius is comparable to the size of the orbit, Jupiter is not spherical, and because the full moon varies quite a lot in size.
(This point was based on a stupid error of mine, well pointed out by Ruslik0. please disregard the rest of this point!) Firstly, for the angle of Jupiter in Amalthea's sky one should use arctan rather than arcsin: as per 
  
    
      
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        a
        n
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          R
          
            J
          
        
        
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        =
        42.89
        
          

          
          
            o
          
        
      
    
    {\displaystyle 2arctan(R_{J}/R_{o})=42.89{}^{o}}
  
 for Jupiter equatorial width.
The angular size of Jupiter is twice the angle between direction to the center of the planet and the tangent to to the visible surface. If you draw simple graph, you will see that this is 
  
    
      
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    {\displaystyle arcsin}
  
 not 
  
    
      
        a
        r
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    {\displaystyle arctan}
  
. So the visible size of Jupiter is 46.2°.Ruslik 18:38, 10 September 2007 (UTC)
Sure, we can do it with arcsin but the length of the ray that makes a tangent with the visible surface is 
  
    
      
        
          
            
              R
              
                o
              
              
                2
              
            
            +
            
              R
              
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    {\displaystyle {\sqrt {R_{o}^{2}+R_{J}^{2}}}}
  
 not 
  
    
      
        
          R
          
            o
          
        
      
    
    {\displaystyle R_{o}}
  
, so if we want arcsin it should be the more complicated 
  
    
      
        2
        
          
            a
            r
            c
            s
            i
            n
          
        
        (
        
          R
          
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              R
              
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        =
        42.89
        
          

          
          
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    {\displaystyle 2{\rm {arcsin}}(R_{J}/{\sqrt {R_{o}^{2}+R_{J}^{2}}})=42.89{}^{o}}
  
. Deuar 09:43, 11 September 2007 (UTC)
The length of the ray is 
  
    
      
        
          
            
              R
              
                o
              
              
                2
              
            
            −
            
              R
              
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    {\displaystyle {\sqrt {R_{o}^{2}-R_{J}^{2}}}}
  
. The formular with arctan is wrong also by a different reason. What is the angular size of Earth when you standing on its surface, i.e. when Ro=Rj? I am sure it is 180°. However you formular will give 90°. The formular with arcsin gives the right answer. Ruslik 11:40, 11 September 2007 (UTC). See also figure.Ruslik 12:09, 11 September 2007 (UTC)
You're absolutely right. Duh. Sorry for all the mix up! Deuar 20:41, 11 September 2007 (UTC)
Why bullets? Aminabzz (talk) 22:13, 12 December 2023 (UTC)
Regarding comparisons with the full moon going beyond the 1st significant digit, the full moon's size varies quite a bit because its orbit is eccentric (0.491°–0.558° across, 0.524° on "average", at least based on my geometry). Furthermore, Jupiter is not round (from Amalthea, it's only 40.34° 43.1° across in the polar direction, as opposed to 46.3° equatorially using the same calculation as in the previous point arcsin calculation, above). This all makes it anywhere from  87.4-76.9 (81.9 average)  83-94  times wider equatorially than the full moon. As for area, Jupiter would be 1730 1570 square degrees, making it  5556-7176 times larger (6300 on average)  6410-8280 times larger.
These calculations have been never supposed to be so precise. Ruslik 18:38, 10 September 2007 (UTC)
Amalthea's orbit is also eccentric, varying by about 0.5% from the mean value used above. This gives a further variation of order 0.2° in Jupiter's dimensions, and about 1% in its angular area.
Conclusion: Jupiter is actually 43° across, and the moon comparison should be "about  80  90 times larger" and "an area about  6000  7000 times greater", without going into too much gory detail. Deuar 22:52, 8 September 2007 (UTC)
Note: to avoid future confusion, I have corrected my calculations after my error was pointed out by Ruslik. Deuar 20:56, 11 September 2007 (UTC)
Brilliant work. This also illustrates well why this section needs proper referencing and cannot be dismissed as too "obvious" to require verification.  I believe that it is acceptable to provide figures based on calculations by editors. However, I think we need links to independent websites or books that provide the formulae for making these calculations. Put simply, if you know how to calculate these figures, that's great, but you need to show how you know. It would be really useful if somebody could provide sources for (a) how one calculates the apparent angular size of one body from another body, and (b) how one calculates the apparent magnitude of one body from another. I realise we already have the formulae in the footnotes, but we need a reference to a reliable source that provides these formulae. Rubble pile 19:21, 9 September 2007 (UTC)
Well, thanks, but you know, as was mentioned above, there are no real references for this kind of stuff. Should we cite our favourite 8th grade geometry textbook? If we really want to have it described  in detail, a solution would be to say something like "see Talk#appropriate section name", or "see [[Amalthea/calc1]]" etc. and write up the argument on the wiki.
A geometry textbook would be better than nothing. Surely there is something, somewhere that explains how how one calculates the apparent angular size of one body from another body, for example? I can't believe no-one has ever written down such a thing ever. But I must admit, I don't know where to look... —Preceding unsigned comment added by Rubble pile (talk • contribs) 12:13, 12 September 2007 (UTC)

What is this?  I clicked on it, which gave me an explaination of what a radius is.  I know that already.  Is this how far away it is from Jupiter?  Jokem (talk) 21:18, 3 January 2009 (UTC)

As part of the WikiProject Good Articles, we're doing sweeps to go over all of the current GAs and see if they still meet the GA criteria. I'm specifically going over all of the "Planets and Moons" articles. I believe the article currently meets the criteria and should remain listed as a Good article. I have made several minor corrections throughout the article. Altogether the article is well-written and is still in great shape after its passing in 2007. Continue to improve the article making sure all new information is properly sourced and neutral. I would also recommend going through all of the citations and updating the access dates and fixing any dead links. If you have any questions, let me know on my talk page and I'll get back to you as soon as I can. I have updated the article history to reflect this review. Happy editing! --Nehrams2020 (talk) 10:07, 20 February 2009 (UTC)

Flammarion suggested the name Amalthée in L'Astronomie, Vol. 12, p. 94 (cite: Jürgen Blunck, Solar System Moons: Discovery and Mythology (2009), p. 10). The trouble is, the ADS record for this is wrong, combining Flammarion's article "Le nouveau satellite de Jupiter" with the following article "Saturne en 1892" by J. Guillaume, and attributes the whole thing to Guillaume. At any rate the code is 1893LAstr..12...91G. It would be cool to add these references at the appropriate spot but I don't know how to handle the ADS error here. --Cam (talk) 04:05, 28 June 2011 (UTC)

Corrected after a request (though some excess pages remained): Bibcode:1893LAstr..12...91F. Stas (talk) 14:06, 18 November 2014 (UTC)

Edward Barnard was well known for opposing use of mythology for naming moons, and called this one Jupiter V only.  Did not use or approve of the name Amalthea, so the article is wrong on the naming.

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Is there any information on what amounts are experienced by the surface of this moon? 50.111.29.1 (talk) 09:33, 9 September 2022 (UTC)

Hi. I think it's also good to mention that Amalthea can cause total solar eclipse on Jupiter. Aminabzz (talk) 22:12, 12 December 2023 (UTC)