Talk:Ceres (dwarf planet)

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Revisiting Flattening[edit]

Since the definition of Dwarf Planet includes hydrostatic equilibrium (and thus an ellipsoid shape), I believe we should add flattening to Ceres's statistics. The last time I brought this up I was asked to show how I arrived at my numbers, step by step, so I shall do so here. I am not a math whiz, so please, feel free to correct me if you see a mistake! (Heck, I probably slaughtered the problem, but hey, gotta learn somehow, right?)

I am using the flattening formula, f = (a-b)/a. Ceres's polar and equatorial radii are listen in its article as: Equatorial radius 487.3±1.8 km Polar radius 454.7±1.6 km.

Using the values: a = 487.3 km and b = 454.7 km, I arrive at f = 0.066899.

I based the uncertainty in the flattening on the uncertainty in the radii, so I calculated the full range of possible flattening by adding and subtracting the max and min radii uncertainties and plugging the new values in to the flattening formula: a = 487.3 + 1.8 = 489.1 and b = 454.7 - 1.6 = 453.1, and thus f(upper value) = 0.073605 and a = 487.3 - 1.8 = 485.5 and b = 454.7 + 1.6 = 456.3, and thus f(lower value) = 0.060144

Then I found the mean value for f from the upper and lower values above (I'm assuming the uncertainty should balance): f = 0.073605 + 0.060144 / 2 = 0.0668745

Then I check to make sure of my balance and get my uncertainty number: 0.073605 - 0.0668745 = 0.0067305 (uncertainty +) and 0.0668745 - 0.060144 = 0.0067305 (uncertainty -)

Therefore I would list flattening for Ceres as 0.0668745 ± 0.0067305

I don't remember if that's exactly what I came up with last time, but my old number was removed (rightly so) pending review and arrival at the correct number. Am I at least boarded on the right train here? --Turboguppy (talk) 23:23, 29 April 2014 (UTC)

Much easier if you calculate the errors directly, once you know the way to do it. Check out here[1] and here.[2] (I'm not claiming those are great sources, but they're the first things that popped up when I searched, and they seemed okay.)
Basically, if you add a and b, you add the absolute errors. When you multiply a and b, you add the relative (%) errors. For a to the b power, you multiply the errors, etc. That's for things like calibration errors, not statistical errors. When dealing with standard deviations like we have here, you want to add the squares of the errors and then take the square root, like finding the hypotenuse of a triangle. Anyway, once you get the hang of it, and can derive a formula for the error for any given formula, you don't have to crank it out by hand and worry if you did it right.
This one[3] is a bit more rigorous, which might make it easier to use, depending on how you process this stuff. — kwami (talk) 01:17, 30 April 2014 (UTC)
Note that flattening alone is not enough for determining hydrostatic equilibrium, since it also depends upon spin, material composition, and internal differentiation models. E.g., see Saturn. So I don't think it's very relevant; however, the planets' articles seem to have it, so why not Ceres?
Anyway, I think the number should be f = 0.066899 +(0.073605-0.066899) - (0.066899-0.060144), which is 0.066899 +0.006706 -0.006755. (assumuming you did the calcs correct above) I.e., nominal +(max-nominal) -(nominal-min). But I don't know how these things are done, either, so check kwami's refs. And if you do some reasonable significant digits, it's just 0.067 ± 0.007 whichever way you do it.
Note that we'll have accurate info in a year or so, and the error bars should be small enough to ignore, so I think this is mostly an educational exercise, and hopefully fun. Tbayboy (talk) 04:05, 30 April 2014 (UTC)
If it depends on composition, then the object is not in HE and so not a DP. Since icy moons 50% larger than Ceres have turned out to not be in HE after all, I do wonder about Ceres. It might be difficult to tell, since its spin might not have changed much over its history.
BTW, the flattening comes out as ±7.4%, or 0.067±0.005. — kwami (talk) 07:01, 30 April 2014 (UTC)
The composition thing is true of any body. It's not so much the raw material as it is the distribution of different materials (the differentiation), which change the gravity slope. Heavy-core with light-mantle gives a different flattening than an evenly dense body, and the relative densities of the layers affects the degree of flattening (assuming a spin, of course). That's why it was so hard to figure out Iapetus for certain, since the error bars for some internal models went within HE until more accurate measurements pushed them all outside. Tbayboy (talk) 12:39, 30 April 2014 (UTC)
You're right, of course. — kwami (talk) 21:04, 30 April 2014 (UTC)
I am not sure that you can calculate the errors for flattening in such a simple way—by treating polar and equatorial radii as two statistically independent variables. They are not because they are model dependent and were obtained by fitting some shape model to the available observations. Calculating errors in this way would be original research. Unless some reliable sources are found, flatting can be only claimed to be around 7% but not more than that. Ruslik_Zero 13:19, 1 May 2014 (UTC)
Well, that throws a wrench in things. I doubt merely rounding would help. The axes are both given to ±0.36%, but if the flattening comes from the model, we can't infer precision from them at all. Wouldn't we need to say "0.067 (assumed by model)" or something? — kwami (talk) 17:19, 1 May 2014 (UTC)
How about forget the ± and use the approx: "~0.07"? Tbayboy (talk) 12:40, 2 May 2014 (UTC)
That might mislead readers into thinking that it is a measured value, or directly derived from measured values, rather than being generated by the model used to predict the shape of Ceres. If someone uses the flattening and spin rate to gain some insight into the structure of the asteroid, they're only recovering the structure assumed in the model.
I agree that if we had a measured value, that would be useful to include, but this is not. I think we should either note that it's artificial or omit it entirely, like we do unknown albedos. — kwami (talk) 16:48, 2 May 2014 (UTC)
On further reflection and after reading all the great posts here, I think I agree most with just leaving it off until we have an actual measurement, to avoid confusion. I'm grateful to everyone who helped me understand the problem better. Thank you!Turboguppy (talk) 06:32, 4 May 2014 (UTC)
Not to mention the fact that equitorial and polar radii are listed and there's no reason - at least none given - to compute a value from them (ie. flattening) which hasn't been shown to be generally useful. Those who want it, can easily calculate it, can't they? (And of course the other readers, the 99.999%, could care less.)Abitslow (talk) 17:51, 21 January 2015 (UTC)

Escape velocity[edit]

We had the escape velocity as 0.51 m/s², "calculated based on the known parameters". NASA has 1.855. Either NASA screwed up or we did, and if we did, there may be (probably are) other articles w the same error. — kwami (talk) 22:40, 11 April 2014 (UTC)

If you're talking about this NASA page, it's in km/h, not m/s. Looking at List of gravitationally rounded objects of the Solar System, .51 is about right (comparing it to similarly sized moons). Tbayboy (talk) 23:00, 11 April 2014 (UTC)
For a Ceres-sized object to have an escape velocity of 1.885 km/s, it will need a density of more than 25g/cm3!. Ruslik_Zero 12:57, 1 May 2014 (UTC)


Look again, it says km/h. — Preceding unsigned comment added by 50.32.226.40 (talk) 13:36, 1 September 2014 (UTC)

King[edit]

I am not sure if the king mentioned was Ferdinand the First or Ferdinand the Third. — Preceding unsigned comment added by 217.42.237.209 (talk) 10:39, 1 January 2015 (UTC)

Which image for infobox?[edit]

So User:Tetra quark has reverted me a couple of times now on this, so I figured I should bring it to the Talk page. Should the image in the infobox be the animated GIF that is a composite of a few frames shot by Dawn on its approach to Ceres, or should it be a processed still image, with the animated GIF appearing further down in the article?

My reasoning behind preferring the latter approach is: 1) it comports better with articles about other Solar System bodies (we don't use an animation of Earth, Jupiter, or the Sun in their infoboxes, for instance); 2) the GIF requires a lengthier caption to explain what it depicts, which is better suited to a thumbnail image than an infobox, IMO; and 3) in a few weeks' time, Dawn will be returning much higher-quality still images of Ceres, and the animated GIF will likely end up relegated to a position further down in the article, as it was in my edit, if it is still used.

I'm open to hearing what other editors have to say about the issue. -Kudzu1 (talk) 08:09, 21 January 2015 (UTC)

@Kudzu1: Thanks for bringing this discussion here and sorry if I seemed rude or anything.
1) I understand your point, but the lead images of Earth, Sun, etc have very good definitions. It is better to use an animation when the quality is low (see Pluto, for example).
2)I agree. The thing is that the caption of that image is unnecessarily long. I would cut it by half if I could.
3)So, in a few weeks we'll change the image. Tetra quark (don't be shy) 08:20, 21 January 2015 (UTC)
FWIW - *entirely* agree with the comments made above by User:Tetra quark - yes, image caption could be trimmed a bit I would think - hope this helps in some way - Enjoy! :) Drbogdan (talk) 12:24, 21 January 2015 (UTC)

Yes check.svg Done - BRIEF Followup - image caption trimmed to the following => "Ceres viewed by Dawn, January 13, 2015.[1][2]
(A bright spot and possible craters seem to be key features of this composite animated video.)"
- seems better - *entirely* ok w/ me to rv/mv/ce of course - Enjoy! :) Drbogdan (talk) 12:45, 21 January 2015 (UTC)

  1. ^ Landau, Elizabeth (January 19, 2015). "Dawn Delivers New Image of Ceres". NASA. Retrieved January 19, 2015. 
  2. ^ Chang, Kenneth (19 January 2015). "NASA Spacecraft Get a Closer Look at Dwarf Planets Pluto and Ceres". New York Times. Retrieved 19 January 2015. 
If someone knows how to and is interrested, I have made a stabilized version of the animated GIF of Ceres to replace this jumpy one => https://drive.google.com/file/d/0B6TcblMsDQMWNi1iU3JrSjY2TGs/view?usp=sharing93.196.86.2 (talk) 16:22, 22 January 2015 (UTC)
Yes, the "stabilized" Gif animation *may* be better - however, removing the "flashing" white horizontal bottom border on the animated image may make the animation even better I would think (I'm unable to remove this border with my "Jasc Animation Shop" program for some reason) - in any case - Enjoy! :) Drbogdan (talk) 17:42, 22 January 2015 (UTC)

Image is virtually useless - remove.[edit]

A couple of things. First and most obvious is the photo supposedly showing Ceres from Mars is useless. Ceres is not marked on it! If I had to guess, I'd guess the extremely faint smudge directly to the left of the word "Ceres" is the intended subject. On my monitor it barely registers above background - and I don't think it adds IN ANY WAY to the article. It should be removed for lack of relevance. Second, the "Classification" section contains a mostly irrelevant and incorrect discussion of Pluto and the 2006 IAU vote. It is historically wrong. The debate wasn't "about" Pluto - it was about the impact of the discoveries of several of what may be dozens (or hundreds) of objects of that size in orbit around Sol. It was about historical prescedent and utility. Pluto, discovered in 1930, is never visible to the naked eye and so, other than a couple of decades of grade school text books, is a minimally significant casualty of the new definition. (At least, it could be argued that way.) But what has Pluto to do with Ceres? And is it really relevant to discuss (in an extremely superficial way, without providing the actual context) proposed definitions that DID NOT get approved? That is an extremely nasty can of worms. How is a NON-definition relevant to Ceres' classification? Most of that should be removed. Although how it sweeps out its orbit is probably worthy of discussion and could be linked to the 2006 definition. Third and lastly, the article takes far too many words to say that there is no generally accepted definition for the word "asteroid" and that NASA describes Ceres as an asteroid as well as a dwarf planet; the two terms need not be mutually exclusive, but some sources consider them so.Abitslow (talk) 18:16, 21 January 2015 (UTC)

@Abitslow: I disagree with removing the image. There are few images of Ceres and we should leave them. It's not like we have a better one to add in its place. Plus, the article isn't flooded with images or anything, so it's ok to leave it there.
Regarding the other things you mentioned, you can modify the content yourself if you don't like the way it's presented Tetra quark (don't be shy) 19:17, 22 January 2015 (UTC)
Wow, now that I checked, that image of Ceres from Mars is duplicated. We need to remove one of them from the article Tetra quark (don't be shy) 19:19, 22 January 2015 (UTC)

GIF issue?[edit]

The 25 January animation doesn't look as pretty on my screen as it could. I've tried 3 different web browsers, and the results are the same: extra noise is introduced in the animation when it is shown at a resolution lower than the native one, like it currently is. Is this a known bug/issue? --Njardarlogar (talk) 22:01, 27 January 2015 (UTC)

I see it too. It is annoying. ——Nikolas Ojala (talk) 22:54, 27 January 2015 (UTC)

A webm or apng would be nice. Starks (talk) 01:03, 28 January 2015 (UTC)

Hopefully we will have better images soon.--agr (talk) 01:36, 28 January 2015 (UTC)
Worst visual impression from any serious image I've experienced on Wikipedia in my time! It's like if anyone spreads perfectly gray butter on a glass window and we're observing it from the underside. A still like on http://www.nasa.gov/sites/default/files/thumbnails/image/pia19167_main.png should be preferred. Rursus dixit. (mbork3!) 08:09, 28 January 2015 (UTC)

Since so many had the issue and no fixes have been provided (yet, anyway), I switched to a single frame. The raw frames are having a bigger and bigger Ceres though; so soon we should be done with animations for the infobox. --Njardarlogar (talk) 10:03, 28 January 2015 (UTC)

Gallery[edit]

I don't think a gallery section is needed for this article because I think it does not belong to those articles for whom "a collection of images can illustrate aspects of a subject that cannot be easily or adequately described by text or individual images", per WP:Gallery. Hekerui (talk) 00:04, 28 January 2015 (UTC)

Hi Hekerui. The gallery currently shows the history of the gradually improving quality of the images taken of the dwarf planet. That's something that is not "easily or adequately described by text". Whether or not the article needs a gallery, is highly subjective but I appreciate your opinion. Maybe other editors should decide. Galleries have several advantages, for example they avoid articles to get too cramped with images; and I think Ceres_(dwarf_planet) is a potential candidate to suffer from this fate in the near future (take 4 Vesta for example, and imagine the article without the section "Observations from Dawn", which is basically just a gallery). BR, -- Rfassbind -talk 00:54, 28 January 2015 (UTC)
IMHO the gallery of images of improved observations of Vesta has nothing to do with Vesta per se, who managed fine in 4.6 billion years without observation. That gallery should rather be in Dawn (spacecraft) which was created by carbon based life forms, with whose history the spacecraft correlates. The observation history belongs to the space craft and the carbon based life forms. Rursus dixit. (mbork3!) 08:16, 28 January 2015 (UTC)
Not going to comment on any specific gallery at this point, but images of explorational history help give an idea of where the current understanding of an object comes from; once the understanding based on those images was current, too. Small traces of even what today is considered hopelessly outdated views could still be part of contemporary theory. --Njardarlogar (talk) 17:18, 28 January 2015 (UTC)