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Roche limit

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This article really takes an abstract concept and makes it concrete with some mind-bending examples and thought-experiments. Hats off to User:Bryan Derksen --Doradus 13:57, 18 Aug 2004 (UTC)

The commentary on this article fails to note that when Weisstein's equation is quoted, the negative sign before the second term in the numerator has become positive at Wikipedia. Probably it is best to do it all over or consult Chandrasekhar's "Ellipsoidal Figures of Equilibrium." User:pdn


  • Support - wow, I should go away for a week more often! -- ALoan (Talk) 14:09, 31 Aug 2004 (UTC) Object - it is good, and I have had a further tweak myself, but it seems a bit short for a featured article. At the very least, it needs a diagram or two. -- ALoan (Talk) 15:16, 18 Aug 2004 (UTC)
  • Object - not very clear discussion, especially in the intro. It took me reading the whole article to decipher which clauses in the first sentance go with which concepts. An inline explanation of tidal forces is needed, or else the concept doesn't make any sense. Also too short, there's got to be more to say about it. - Taxman 15:23, Aug 18, 2004 (UTC)
  • Ok. I don't exactly understand the "decipering" objection, since the first sentence seems clear enough to me, but perhaps it is confusing to the lay person. Anyway, I agree the article could use a diagram, and perhaps some sections. --Doradus 18:14, 19 Aug 2004 (UTC)
    • Don't worry, the added dashes make what I noted more clear. But the explanation of tidal forces needs to be worked in more cohesively now. The one sentance notes the term tidal forces, then the next notes what appears to be the definition (but maybe not exactly, as it is not made explicit) of the term tidal forces. Needs to be combined for clarity. I didn't want to add incorrect physics by reworking it myself. - Taxman 18:34, Aug 19, 2004 (UTC)
  • Object, primarily on the basis of length. It will be the Roche limit which, a few million years hence, may make Earth a ringed planet. I'm also concerned that the Roche formula appears so early in the article. This is quite enough to scare away the casual reader who has no mathematics or physics background. Denni☯ 01:56, 2004 Aug 20 (UTC) Support enthusiastically. I applaud the effort which has gone into creating this first-rate physics article. Wonderful illustrations, Theresa!! Denni☯ 18:15, 2004 Aug 27 (UTC)
    • I agree. The formula appears early on as if from nowhere. I would like to see an explanation of where the formula comes from. (Presumably the gravitational forces and tidels forces are equated plus a bit of algebra) As an aside I am happy to draw a diagram if someone cares to explain what they want drawn. [[User:Theresa knott|]] 12:44, 20 Aug 2004 (UTC)
    • I've moved the formula down the page into the second section. The article is now split into two halfs, with the first half being sutable for the casual reader and the second half with the "scary" equations. Theresa Knott 01:46, 23 Aug 2004 (UTC)
      • If you need suggestions for a diagram: Google is your friend ;-) -- Chris 73 Talk 14:08, 20 Aug 2004 (UTC)
        • OK well I could draw something similar to some of those. [[User:Theresa knott|]] 15:26, 20 Aug 2004 (UTC)
      • Also see [1], [2], [3] and [4] for some ideas in context. The text of these is also quite good - perhaps worth checking whether the article covers the same points. -- ALoan (Talk) 16:31, 20 Aug 2004 (UTC)
        • OK I've uploaded Image:Roche limit (two spheres).PNG which is basically an adaptation of the diagram found here I haven't actually put it in the article yet because it needs an explanation and it's late (When I'm tired I make even more mistakes than usual) Feel free to add it in for me, otherwise I'll do it myself later. [[User:Theresa knott|]] 23:03, 20 Aug 2004 (UTC) Done Theresa Knott 20:00, 22 Aug 2004 (UTC)
          • That image explains the theory very well, but do I ask too much if I want an image of satellite approaching, stretched by tidal forces until it disintegrates, like this or this. [[User:Sverdrup|❝Sverdrup❞]] 10:52, 22 Aug 2004 (UTC)
            • Yep I spotted that image too and intend to add another similar one to the article as well. In fact that whole web page is fascinating and it's well worth incoorporating some of the ideas from it into our article. I'll try and do some work on it this evening, if I get time :-( Theresa Knott 14:29, 22 Aug 2004 (UTC)
              • Ive done the additional images. Theresa Knott 01:02, 23 Aug 2004 (UTC)
                • Great. Thank you. -- Chris 73 Talk 01:23, Aug 23, 2004 (UTC)

Holy smokes. Linking the article from here was the best thing that ever happened to it! --Doradus 15:51, 24 Aug 2004 (UTC)

There seem to have been 3 objections, at least two of which have been properly answered. I assume that that will get it approved, with the time limit being up within the next 24 hours. It's a worthy article, and I'm not going to kill it this late, so—

  • Neutral. The derivation at the end is a fine idea, but is much too sketchy to be held up as an example. See the talk page. Dandrake 18:00, Aug 24, 2004 (UTC) Support. It's fixed, so far as I can see, and there was still time to change my vote. Great article. Dandrake 07:40, Aug 25, 2004 (UTC)
    • Wuzzeb and I independently fixed the equations. It is now a more detailed step by step explanation based on the gravitational and the tidal force. I also removed the image that went with the old equations, since the new equations need an updated image. I could do it, but Theresa's images have a nicer feel. -- Chris 73 Talk 02:56, Aug 25, 2004 (UTC)
      • I fixed the image and reuploaded it. Wuzzeb 03:44, 25 Aug 2004 (UTC)

Can we hold off on this article for a few more days until we get the problems with the derivation sorted out? We shouldn't feature an article with incorrect mathematics, yet I don't think it'll take too long to sort it. (I'll get it right eventually) Theresa Knott 00:50, 25 Aug 2004 (UTC) <sauf London accent>sorted</accent>. As far as I can see - all objections have now been addressed. Theresa Knott 08:41, 25 Aug 2004 (UTC)

  • I've done a few final tweaks and checks: looks good to me. -- The Anome 20:20, 25 Aug 2004 (UTC)
  • (not a vote) Two more points: According to the external link, the formula we have is the easy one, and there is a second, more rigorous approach. Could we work this in, too (not necessarily the full derivation, just the different asumptions and the equation)? Second: A list of examples would be nice, e.. what is the roche limit of the moon to the earth, earth to the sun, etc. -- Chris 73 Talk 23:04, Aug 25, 2004 (UTC) Support -- Chris 73 Talk 17:08, Aug 30, 2004 (UTC)
    • The Earth-Moon d apporx. 9,500 km which is only around 3,122 km above the surface. The Sun-Earth d approx. 556, 689 km, which is actually less than the radius of the sun! A better comparison would be the roche limit for different comets, as seen on this page [5]. Wuzzeb 00:39, 26 Aug 2004 (UTC)
      • I just added a significant chunk of text, second approach with different assumptions (although not completely derived), and a table with example results. Please check my text for accuracy. Chris 73 Talk 01:23, Aug 26, 2004 (UTC)
        • Also added an animation. Not sure to where exactly the satellite disintegrates, though. Chris 73 Talk 03:35, Aug 26, 2004 (UTC)
          • Ironically, I have to object now. The animations are a nice idea, but I think they detract from the article. First, the rigid body version is incorrect. The analysis computes where a rigid object would be lifted from the surface of a rigid body, not where the rigid body itself would disintegrate. Second, animations don't work on printouts. Third--and this is just a personal opinion--they are about as visually appealing as the <BLINK> tag. --Doradus 15:31, 26 Aug 2004 (UTC)
            • I agree as well. The pictures in the top section give the idea, and the animation doesn't really add anything. As well, the animation shows the body crashing into the planet, when sometimes the body will still orbit the planet, just not in one lump. As soon as you see the animation, it is pretty jaring since the style is different, blue sun instead of yellow, etc. Wuzzeb 21:25, 26 Aug 2004 (UTC)
  • Still and all, Wikipedia (though being drive space) is not paper. We should not constrain ourselves to still images when it comes to demonstrating a point. While the animated graphics may leave something to be desired in some eyes, I find far more positive than negative to say about them. Denni☯ 18:15, 2004 Aug 27 (UTC)
    • Ok, then what remains objectively is that the rigid body one is incorrect, and that both of them show the body colliding with the planet instead of orbiting it. But I see nothing unclear, that the animations make clear. --Doradus 19:25, 27 Aug 2004 (UTC)
  • Object - both still and animated pictures show an incorrect distortion away from a prolate spheroid shape. As is, they are deceptive. With the new version of the still pictures some other changes I can now support the nomination. Noren 06:49, 28 Aug 2004 (UTC)
    • Hi Noren - you can sign your name by typing four tildes ~~~~. I've changed the still image, and adapted you explanation from the talk page as a caption. Let me know what you think. Theresa Knott (The token star) 23:09, 27 Aug 2004 (UTC)
      • I finally went ahead and axed the animation. It didn't really contain any information not already in the other diagrams. That plus the other problems listed above makes me think the article is better without it. --Doradus 03:22, 28 Aug 2004 (UTC)

This article has undergone a lot of growing pains recently. I don't know the normal procedure for this kind of thing, but it seems reasonable to remove it as a featured article candidate for the time being, and possibly re-nominate it some time in the future. Does anyone feel that it should be accepted at this time? --Doradus 17:00, 28 Aug 2004 (UTC)

Growing pains? The growth was in response to the objections. The whole point of doing all the extra work was to get the article in shape for featured status. I believe that the article is now in good shape, the objections have largely been addressed, and so it should not be removed from this page. I am happy to support the nomination for featured status. Theresa Knott (The token star) 20:38, 28 Aug 2004 (UTC)
Yes, but the article has increased in size by a factor of four since this hurricane of editing started. There is more new text than old. That's growing pains. I think we all need some perpective on the article before we're qualified to decide if it's in good shape. I'd like to have some time to forget about it a bit and then re-read it in a week or two before we find our freshly-mined gem on display for the world to see. However, this is not an objection. I'll abstain. --Doradus 18:29, 30 Aug 2004 (UTC)

I support. Great article. Good topic, good info, well-explained. The kind of thing we need more of. Alteripse 22:48, 28 Aug 2004 (UTC)

Support. The collaboration and content shine. Congratulations. Ancheta Wis 15:42, 1 Sep 2004 (UTC)

Object, until somewhere in the non-technical section there's some explaination of the magic phrase "tidal force" the lay user won't understand. -- Kop 00:28, 3 Sep 2004 (UTC)

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