When reading this discussion I think it's important to bear in mind wp:TECH-CONTENT

May you explain why exactly you think this comet's orbit doesn't have a semi-major axis? RE your reversion titled "There is no (useful) semi-major axis at that epoch" 84.12.140.139 (talk) 02:12, 27 September 2015 (UTC) [reply]

With an eccentricity greater than 1, C/1980 E1 is on an ejection trajectory and no longer orbits the Sun. You can not just list a negative semi-major axis without misleading readers. You will need to give a very detailed explanation as to why it is not the objects average distance from the Sun. -- Kheider (talk) 13:18, 26 September 2015 (UTC)[reply]

The comet is on a hyperbolic trajectory. Hyperbolas certainly have a semi-major axis. If you do not believe this to be a case, you should contact the jpl and ask them to remove the semi-major axis field of this (and many other) comet's orbital elements table: http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=1980%20E1 ! Please revert your reversion, and correct any other pages you may have vandalized. I suggest you brush up on your orbital mechanics, here might be a good place to start: https://simple.wikipedia.org/wiki/Orbital_mechanics — Preceding unsigned comment added by 84.12.140.139 (talk) 14:23, 26 September 2015 (UTC)[reply]

Please read Hyperbolic trajectory. -- Kheider (talk) 14:28, 26 September 2015 (UTC)[reply]

Which part? The bit where it says "a is the negative semi-major axis of orbit's hyperbola." perhaps?

It is misleading to show a semi-major axis for an object on an ejection trajectory. Notice how the JPL SBDB does NOT list aphelion? -- Kheider (talk) 16:05, 26 September 2015 (UTC)[reply]

I'm not going to accept that assertion without any evidence. The semi-major axis is one of the defining parameters of a hyperbolic orbit and you're suggesting that people would be misled by including this important information. Please state what exactly you believe the presence of this useful information will lead them to believe. The SBDB doesn't list the apoapsis because this object is on an escape trajectory, so at no point will it reach it farthest away point; I don't see what this has to do with including information on the semi-major axis though... Perhaps you are confused with the difference between the apoapsis and the semi-major axis of an orbit? 84.12.140.139 (talk) 17:09, 26 September 2015 (UTC)[reply]

For the average reader it is about a useful as showing the solution to the square root of "-4". -- Kheider (talk) 17:27, 26 September 2015 (UTC)[reply]

Firstly, I don't think that the "average reader" will be reading an article about an obscure comet, in the same way that articles about complex numbers aren't read by average readers. Secondly, just because the correct information might be confusing is absolutely no reason to censor it. I found it far more confusing to see that the semi-major axis field was "Not Applicable" (I see that this has now been revised). 84.12.140.139 (talk) 19:02, 26 September 2015 (UTC)[reply]

(talk page stalker) Anon, listing either perihelion, semi-major axis, or aphelion (which in this case does not exist) alongside eccentricity (and four other parameters not relevant to this discussion) is sufficient to uniquely determine an orbit. Perihelion is listed, hence its orbit is uniquely determined by those values. Semi-major axis does not serve that purpose and listing a negative value, though technically correct, does not normally mean much to a reader, and hence is not useful. --JorisvS (talk) 17:54, 26 September 2015 (UTC)[reply]

In this effort to eliminate redundancy do you also propose to remove this parameter from the table on this page. I think that nearly every maths article has derived values and equations which could also be culled too! If you're so concerned that readers aren't going to be able to understand this then perhaps the negative value could link to the article on hyperbolic orbits, or have a note attached explaining this mathematical quirk. It seems arbitrary to decline including this information just because it's negative, thank goodness that the inclination is greater than zero or this might not be included too! I dispute that this value is not useful, I came to this page specifically for this information (expecting a negative value I should add). 84.12.140.139 (talk) 19:02, 26 September 2015 (UTC)[reply]

That's apples and oranges. A positive semi-major axis is very meaningful to most if not all readers. And inclination is positive—it's a value between 0 and 180°. A negative inclination is the same as a positive one with the ascending node 180° different. What did you want to do with its semi-major axis value? --JorisvS (talk) 19:10, 26 September 2015 (UTC)[reply]

Obviously the comparison to derived equations in mathematics articles was for effect, but I believe that it's inconsistent to remove the semi-major axis field here and not for every other orbit for which the periapsis or apoapsis is given. I was being flippant about the inclination. I imagine that the set of readers for whom the term "semi-major axis" is meaningful but whose brains explode on seeing a negative value there is very small indeed. Any reader who thinks that the semi-major axis for a conic section must be positive is misinformed. The page for semi-major axis doesn't say anywhere that the value must be positive, in fact in the third paragraph it specifies that the value may lie either side of zero. Every other equationfor hyperbolic orbits on Wikipedia is in terms of the (negative) semi-major axis, and not in terms of the periapsis, in fact the only equation I can find elsewhere which is written in terms of the periapsis is one to find the semi-major axis! 84.12.140.139 (talk) 19:45, 26 September 2015 (UTC)[reply]

A negative semi-major axis for hyperbolic trajectories is mathematically sound. For elliptical orbits the interpretation of the semi-major axis is straightforward: the average distance. However, this interpretation makes no sense for a negative semi-major axis. That's the big difference. --JorisvS (talk) 23:11, 26 September 2015 (UTC)[reply]

I'll ask the question more directly: what is it that you think will happen if a reader encounters a negative value for a semi-major axis when she is not expecting it; the most likely outcome I can think of is that she ends up learning something new, a worthy outcome indeed. It's worth noting that the average distance is only valid when one takes the average over the eccentric anomaly. If you consider this the sole reason for inclusion of the semi-major axis on all the elliptic orbits listed on Wikipedia I'd ask you why the semi-minor axis isn't listed as it too has every right to be the "average distance" of the orbiting body; I'd posit that the semi-major axis is included elsewhere because it's far more useful in its own right! The interpretation for the semi-major axis for elliptic orbits and hyperbolic orbits is exactly the same as the interpretation of the semi-major axis for ellipses and hyperbolas, i.e. half the distance between the intercepts of the line passing through both foci. If the little minus sign causes you so much grief, feel free to use a positive value and fly in the face of convention elsewhere... 84.12.140.139 (talk) 23:52, 26 September 2015 (UTC)[reply]

C/1980 E1 is being ejected from the Solar System. To suggest to the reader that it has an average distance of 58AU from the Sun is horribly misleading. Numerical integration shows that after 2013-Dec-24, it will *never* again be 58.268AU from the Sun. Why do you want to mislead the readers? -- Kheider (talk) 00:45, 27 September 2015 (UTC)[reply]

I think you misunderstand what the semi-major axis is used for, it has a significance far beyond the average distance of an elliptic orbit. My intention in putting this information into the article was clearly not to mislead; I decided to put it in because I myself had come looking for this information and hoped I could improve the experience of others coming after me. 84.12.140.139 (talk) 01:19, 27 September 2015 (UTC)[reply]

@84.12.140.139 and JorisvS: You may want to consider (a) moving the discussion to the article talk page, (b) look into a WP:Request for comment, (c) if the issue is not resolved after extensive discussion on the article talk page, file the case at WP:DRN, although that should not be necessary if the WP:Request for comment goes as intended. --JustBerry (talk) 01:30, 27 September 2015 (UTC)[reply]

Wikipedia talk:WikiProject Solar System or Wikipedia_talk:WikiProject_Astronomy might be better places to get an informed opinion. -- Kheider (talk) 01:40, 27 September 2015 (UTC)[reply]

Your average reader will not know what a negative semi-major axis is. Without explaining "in detail" what a negative semi-major axis means, I can not see how listing an unexplained negative semi-major axis is going to help the layperson. Wikipedia readers have a hard enough time understanding that different epochs generate different orbits. -- Kheider (talk) 01:33, 27 September 2015 (UTC)[reply]

That argument could be made about innumerable topics on this website, and is no reason by itself to not include information. My suggestion earlier was to attach a note to the value either linking to Hyperbolic trajectory or Semi-major axis or even just to say "The semi-major axis of hyperbolic orbits is negative by convention" 84.12.140.139 (talk) 01:40, 27 September 2015 (UTC)[reply]

I see more of a wp:TECHNICAL issue than adding something useful to the reader. You would need to write a paragraph or more to explain why listing a semi-major axis for an object being ejected from the Solar System is useful to the infobox. I think it creates more of a problem than it solves. The article is already technical compared to most comet articles. -- Kheider (talk) 01:54, 27 September 2015 (UTC)[reply]

I disagree that that paragraph would be necessary, one doesn't see the equivalent paragraph next to the semi-major axis value on any other page. The article Semi-major axis states in the opening paragraphs that the value may be negative. A quote from wp:TECH-CONTENT sums up this discussion pretty well I think: "Wikipedia strives to be a serious reference resource, and highly technical subject matter still belongs in some Wikipedia articles. Increasing the understandability of technical content is intended to be an improvement to the article for the benefit of the less knowledgeable readers, but this should be done without reducing the value to readers with more technical background .... Making articles more understandable does not necessarily mean that detailed technical content should be removed. For instance, an encyclopedia article about a chemical compound is expected to include properties of the compound, even if some of those properties are obscure to a general reader". 84.12.140.139 (talk) 02:08, 27 September 2015 (UTC)[reply]

Again, *suggesting* to the average reader that this comet has an average distance from the Sun of 58AU is horribly misleading. It would require a detailed explanation to prevent creating more problems than it solves. -- Kheider (talk) 02:13, 27 September 2015 (UTC)[reply]

That's like saying "Listing Chlorine's atomic weight as 35.5 will bamboozle readers into thinking it has a non-integer number of baryons so we should leave it out of the article". I think if a reader doesn't understand that then they are generally savvy enough to follow the link to "Atomic Weight" or "Semi-major axis" and work it out if they're interested rather than "causing problems". It's immediately clear that a body can't have a negative distance to another. Please also read my reply to your other message containing "horribly misleading". I think that what I'm saying isn't getting through, so I'll try to leave the discussion here and wait for further comments 84.12.140.139 (talk) 02:38, 27 September 2015 (UTC)[reply]

It is as misleading as suggesting C/2012 S4 (PANSTARRS) has a semi-major axis of 250,000 AU (4.0 ly) from the Sun. — Preceding unsigned comment added by Kheider (talk • contribs)

We could write a note explaining what a negative semi-major axis means. --JorisvS (talk) 09:33, 27 September 2015 (UTC)[reply]

I'd be happy to compromise with that. Perhaps something like "Hyperbolic trajectories use the negative semi-major axis" 84.12.140.139 (talk) 10:01, 27 September 2015 (UTC)[reply]

I was thinking something more elaborate. "C/1980 E1 is on an escape trajectory out of the Solar System, i.e. it has a hyperbolic orbit. For a hyperbolic orbit the semi-major axis is still defined, but is negative. Therefore, this value cannot be interpreted as average distance, but mathematically [something on the mathematic definition]." I don't know to where on semi-major axis you want to refer the reader, though, because says nothing about negative semi-major axes. --JorisvS (talk) 10:59, 27 September 2015 (UTC)[reply]

I had in mind the reader seeing "...plus or minus one half of the distance between the two branches" on Semi-major axis. I think that the article on hyperbolic trajectories could be improved in this respect. How about the following "For a hyperbolic trajectory the semi-major axis is defined and the negative value is used by convention as it enables many of the same orbital parameters to be calculated using the same formulas as for elliptic orbits. Please note that the semi-major axis for a hyperbolic trajectory doesn't represent any kind of average distance.". To be honest, I think this information would be better placed in a section in Hyperbolic trajectory or even Semi-major axis to prevent it from having to be copied to any other articles featuring hyperbolic orbits; it's not specific to this article. Is there a way to share footnotes between articles? 84.12.140.139 (talk) 11:30, 27 September 2015 (UTC)[reply]

Being on an escape trajectory doesn't imply a hyperbolic orbit (It could be parabolic or non-keplerian (influenced by multiple bodies)), perhaps instead of being prefixed with "i.e." that clause would be better being enclosed in parentheses. 84.12.140.139 (talk) 11:33, 27 September 2015 (UTC)[reply]

These quantities are also related by the equation q equals a(1-e), so when e>1, a goes negative. I am still not convinced the average backyard astronomer will get any added value from listing a negative semi-major axis. But I have added the comment, "The orbital energy is inversely proportional to negative semi-major axis. Objects in hyperbolic orbits have negative semi major axis, giving them a positive orbital energy." to the footnote. -- Kheider (talk) 18:01, 27 September 2015 (UTC)[reply]

The note aboute the negative semi-major axis meaning a positive orbital energy is very helpful. --JorisvS (talk) 18:24, 27 September 2015 (UTC)[reply]

I'm not convinced that a chef or a pianist will get any added value from listing the eccentricity in this article; it's important to remember that Wikipedia has a broad user-base and that not everybody shares your exact interests. 84.12.140.139 (talk) 21:09, 27 September 2015 (UTC)[reply]

It has been listed with an explanatory note. I thought that was the point. What else do you want from us here? --JorisvS (talk) 07:52, 28 September 2015 (UTC)[reply]

I was merely replying to the comment: "I am still not convinced the average backyard astronomer will get any added value from listing a negative semi-major axis." 84.12.140.139 (talk) 09:06, 28 September 2015 (UTC)[reply]

• I have been summoned to this RfC, but I see no explanation of what the point of contention is. So I will make a couple of comments.

1. The tautological phrase "apoapsis distance" could be replaced by the standard term "aphelion".
2. I found the article itself easy to understand. (I am not an astronomer, but I have a science degree. I know what elliptical and hyperbolic orbits are.) The footnote "a" was harder work, but I managed to understand it. It contributed nothing to my understanding of the subject. The article would be better without the footnote.

Maproom (talk) 08:15, 11 October 2015 (UTC)[reply]

• Largly agree with Maproom. For one thing the footnote as it stands contribute nothing special. Its content would be of more value if incorporated coherently into the text.
  As for the idea of omitting relevant details because some readers might not understand them, I strongly oppose it. Where practicable the details should be explained comprehensibly; where not the relevant material should be incorporated either in a separate section that non-technical readers could skip easily, or in some convenient manner that is easy to skip anyway.
  The footnote no doubt was intended as such, but the effect was not satisfactory. Bad luck, but it does not invalidate the principle.
  In this case, the fact that the semi-axes are defined is sufficient justification for their inclusion, possibly with suitable links to articles dealing with hyperbolas or hyperbolic orbits. Readers who don't understand probably will not know what semi-axes are and will ignore the material anyway. Readers who wonder how a hyperbola can have a semi-major axis then can follow a link if they are sufficiently interested; it is not for us to dictate what they should want to read or skip. Readers who DO understand, then will not be caught short by having to look up the value elsewhere instead of having it conveniently to hand. JonRichfield (talk) 12:17, 15 October 2015 (UTC)[reply]

• I also have been summoned to the RfC. If there are references to support two different explanations or descriptions of the the comet and its trajectories, then include them both. I barely understand the article even though I am acquainted with the topic of astronomy. I am better versed in biological and chemistry topics. From what I can see of the discussion, there is some contentiousness and harsh, personal attacks. With this kind of exchange it is difficult for me to see what the solution could be that would be acceptable to each editor. Even though no one has asked, this article is too technical for the average reader. I typically recommend that we write for an audience of 8th graders. Best Regards,

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