Talk:Halley's Comet

ref label b?

In "Structure and composition" is "^[b]" which seems to do nothing. Anyone know what this is for or how to fix it? Al Begamut (talk) 22:47, 6 April 2024 (UTC)

@Al Begamut: This has been the case since the article was vandalized on 8 March 2010, 14 years ago.[1] The edit was partially, but not completely, reverted 12 minutes later,[2] by what may well have been the same editor who originally vandalized it (both were made by unregistered IPs). The page syntax has been broken ever since. It should work again now.[3]

I have never seen a Featured Article that had such blatant vandalism stand for so long. Renerpho (talk) 06:35, 29 June 2024 (UTC)

I appreciate very much your detailed explanation; as an editor with limited range of experience, this insight is helpful to me. Al Begamut (talk) 13:12, 29 June 2024 (UTC)

@Al Begamut: This is now listed at Wikipedia:Wikipedia records#Vandalism, as the longest undetected vandalism on a featured article. Thanks again for bringing it to our attention! Renerpho (talk) 19:08, 29 June 2024 (UTC)

Wow, all right then. Pleased to have helped! Al Begamut (talk) 12:50, 1 July 2024 (UTC)

684 CE depiction?

The table of apparitions claims that the comet is depicted in the Nuremberg Chronicle, which for some time was thought to be the oldest depiction of a comet. This claim, which was popular since the 1960s, has been disproven in 1989. I don't know why it is in this Featured Article, and with a source from 1985! Renerpho (talk) 06:00, 29 June 2024 (UTC) Renerpho (talk) 06:00, 29 June 2024 (UTC)

I removed both mentions of it. Renerpho (talk) 19:09, 29 June 2024 (UTC)

References

Considering nomination for FAR

I am considering nominating this article for Featured Article Review. Looking at the article talk page, it is apparent that nobody is taking care of the maintenance of this level-4 vital article. There has been a case of blatant vandalism that was introduced two months after the article was promoted to FA status, in March 2010, which broke the page syntax. The issue was raised on the talk page three months ago, with no replies. I just corrected it now, after it stood in the article for 14 years.[4]

This was just after I had tagged a claim about a historical observation of the comet as dubious (what to do about it remains to be discussed, see Talk:Halley's Comet#684 CE depiction?). That particular claim was popular since the 1960s, but was disproven in 1989. It stands in the article twice -- first with a source from 1985, and then a second time without a source. It was first introduced in January 2009,[5] and has remained completely unreferenced for a long time (only to be eventually referenced with an outdated source, rather than be removed). While not as outrageous as the vandalism, it suggests to me that this article has not been thoroughly reviewed in December 2009, or when it became a FA in 2010.

I didn't look very hard... What else is there that to be found that could disqualify this article from FA status? Renerpho (talk) 07:03, 29 June 2024 (UTC)

If you are going to take this to FAR, I expect you to be here for the long haul. Your FAR of Sedna was a farce. You disappeared after 4 days and left me to carry the load for a clueless review team for eight solid months. And the article wasn't ultimately changed much at all. I fully expect this FAR to go exactly the same way. I hope you're willing to prove me wrong. Serendi^podous 13:08, 29 June 2024 (UTC)

@Serendipodous: Following that last FAR, I said I'd probably not nominate anything for FAR again. I've been discussing this question off-wiki today, and I decided I won't nominate Halley's Comet, because that's an experience I don't want to repeat (for myself, and others).

That doesn't mean that there aren't problems with the references for this article, beyond what I said before: Renerpho (talk) 20:34, 29 June 2024 (UTC)

Resolved issues

Fixed WP:MOS issues

•  Fixed The article uses both American and British English ("kilometres", but "colored"). Which one is it supposed to be? Renerpho (talk) 06:58, 6 July 2024 (UTC)

  I would argue that it should be British English. The original article was an excerpt from a 1911 encyclopedia;[6] most likely the Encyclopedia Brittanica.[7] It includes the word "sabre", which is the British English spelling. The fact that Edmond Halley was an English astronomer would further support that usage. Praemonitus (talk) 18:52, 6 July 2024 (UTC)

  I've converted the instances of AE I found to BE (except in direct quotes), and did the same for dates that weren't DMY. Renerpho (talk) 03:35, 7 July 2024 (UTC)

•  Fixed Quote: Evaporation of this dirty ice releases dust particles, which travel with the gas away from the nucleus. -- As we establish two sentences earlier, the release process is sublimation, not evaporation. There is no liquid on the comet that could evaporate. Renerpho (talk) 07:34, 6 July 2024 (UTC)

  I've changed this accordingly. There are instances in the article that still use the word "evaporate", like in the section about the 1835 apparition (observations of streams of vapour prompted Bessel to propose that the jet forces of evaporating material could be great enough to significantly alter a comet's orbit). Since this is a contemporary observation, not a scientific fact, I leave it as is. Renerpho (talk) 04:09, 7 July 2024 (UTC)

Fixed problems in lede section

•  Fixed There are a number of citations in the lede section that don't look controversial to me. The reference for the orbital period doesn't seem necessary, and the reference that the comet was named after Halley doesn't actually do much (it leads to an article published by Halley himself -- so what?). Surely we don't need a primary source for this claim anyway? Do you think we can get rid of those, and the others? Renerpho (talk) 22:35, 29 June 2024 (UTC)
•  Fixed As FlightTime alludes to in their edit summary here, we mention the designation 1P/Halley in the lede, so we should probably discuss it in the article, too. Outside of image captions and in the references, we don't bring it up ever again after the first paragraph!
  In the Apparitions section, the article says: For example, "1P/1982 U1, 1986 III, 1982i" indicates that for the perihelion in 1986, Halley was the first period comet known (designated 1P) and this apparition was the first seen in half-month U (the second half of October) in 1982 (giving 1P/1982 U1); it was the third comet past perihelion in 1986 (1986 III); and it was the ninth comet spotted in 1982 (provisional designation 1982i). That's quite complicated and clumsy, and it's bad English, too. I have no idea what a "period comet" is, and the meaning of the designation 1P doesn't actually depend on the perihelion in 1986. If we really need to explain the different designations, we should probably do so much earlier, maybe close to the Pronunciation section. Renerpho (talk) 11:45, 4 July 2024 (UTC)

  A minor, related issue: It can be called Comet Halley -- it can be called Larry, too. What matters is that it is often called Comet Halley. I'll go and change it accordingly. Renerpho (talk) 12:05, 4 July 2024 (UTC)

Fixed problems in Computation of orbit section

(None yet)

Fixed problems in Orbit and origin section

•  Fixed I have replaced one instance of the Keller (2005) reference with the original paper by Hughes (1985). Keller mentions Hughes' result in passing, but his version of it isn't quite what the original source said.[8] It may be worth checking all references for whether they are the original source, or are just citing someone else's work. The original is usually preferable, due to instances of Chinese whispers like this. Renerpho (talk) 00:34, 1 July 2024 (UTC)

  I have started doing so, beginning with the references to JPL (see below). Renerpho (talk) 02:11, 1 July 2024 (UTC)

•  Fixed Quote: The orbit is inclined by 18° to the ecliptic, much of it lying south of the ecliptic -- This immediately precedes the sentence in brackets about the retrograde orbit (see above), and the source there[9] doesn't support it. We are missing a reference for this -- particularly for the second part of the sentence, that much of it lies south of the ecliptic. Renerpho (talk) 06:19, 6 July 2024 (UTC)

Fixed problems in Structure and composition section

•  Fixed I have added an archived URL to the dead ref. 8 ("What Have We Learned About Halley's Comet?"), but I am not convinced that this is a reliable source for the kind of information it is used for in our article. It's not peer-reviewed, doesn't cite sources, and the authorship is unclear. Luckily, it looks like we're not using it for anything wild, so it should be possible to replace it. I'll start working on that right way. Renerpho (talk) 00:45, 1 July 2024 (UTC)

  Replaced with Reitsema, Keller1987 and Altwegg1993. The size of the coma given in the old reference disagrees with the size given in Altwegg1993, by a factor of about 5. Altwegg1993 actually shows the measurements done by the Giotto spacecraft, and appears much more reliable. Renerpho (talk) 01:31, 1 July 2024 (UTC)

•  Fixed Note b ("Jet Propulsion Laboratory lists its average diameter as only 11 km") is an editorial statement that may be undue. JPL doesn't say "average diameter", but most likely refer to its mean diameter (and that's how we use it in the infobox, too). Using the formula from mean diameter, the dimensions given before would result in a diameter of $(15\cdot 8\cdot 8)^{1/3}=9.9$ km, so the word "only" is not justified. I've rephrased it. Renerpho (talk) 00:55, 1 July 2024 (UTC)

  I have now moved the note into the main text, and have completely removed JPL as a source for the size. The primary source, as used by JPL, is Lamy (2004), who specify that they're talking about mean radius (diameter) on p.230, and who explain in more detail how they got from the three axes (per the snapshots taken by Giotto and the Vega spacecraft) to an effective size. The numbers, previously looking inconsistent (11 vs. 9.9), make sense with their adjustments. Renerpho (talk) 02:07, 1 July 2024 (UTC)

•  Fixed In the Structure and composition section, we are using two different sources for the comet's mass (M=2.2 × 10¹⁴ kg) and density (d=0.6 g/cm³). That's fine in principle, but the two are inconsistent with each other. They'd result in a volume of M/d=367 km³, or an effective radius of 4.4 km,[10] 20% too low. Can't we find a source that gives both mass and density, in a way that is more consistent with what we know about the comet's size? Renerpho (talk) 02:31, 1 July 2024 (UTC)

  Note that the density we give in the main text doesn't reflect what we say in the infobox, where we give a wide range of possible densities (0.2–1.5 g/cm³). With that, the problem of inconsistent mass/density goes away, as long as we don't rely on the value of 0.6 g/cm³ too much. Renerpho (talk) 02:33, 1 July 2024 (UTC)

  Reading ref. 17, on p.213, near the end of the right column it gives consistent mass, density and size estimates, together with sources for each. Maybe we should just switch to that. Renerpho (talk) 02:58, 1 July 2024 (UTC)

  The numbers given in ref. 17 are: M=1–3 × 10¹⁴ kg, V=365 km³, d=550±250 kg/m³. These also give a better indication of the uncertainties involved. The source given in ref. 17 for the mass is Rickmann H. (1989), Adv. Space Res., 9(3), 59–71, where the name is an apparent misspelling of Hans Rickman. His article is not only younger than our source (Cevolani, 1987), but also doesn't claim more than the data supports. The original numbers from Rickman are: M=1.3–3.1 × 10¹⁴ kg, d=0.28–0.65 g/cm³ (that density is based on an unspecified size estimate, so the density in ref. 17 is more reliable).

  Are there any objections against replacing ref. 9 and 10 by "ref. 17 plus Rickman"? Renerpho (talk) 03:14, 1 July 2024 (UTC)

  Go ahead. Serendi^podous 13:48, 1 July 2024 (UTC)

   Done Renerpho (talk) 11:20, 4 July 2024 (UTC)

•  Fixed The article states that Changes in the flow of the solar wind can cause disconnection events, in which the tail completely breaks off from the nucleus, where the wiki-link leads to Comet. That article says nothing more about what a disconnection event is than we're doing here. I don't know if the wiki-link should be replaced entirely, removed, or if we just need to do a better job explaining what it means. Note that disconnection event as a redirect is different from what we are doing. Renerpho (talk) 02:44, 1 July 2024 (UTC) We now have a better source for this. Renerpho (talk) 08:18, 4 July 2024 (UTC)
•  Fixed Quote from the article: Although only 25% of Halley's surface was imaged in detail during the flyby missions, the images revealed an extremely varied topography, with hills, mountains, ridges, depressions, and at least one crater. The reference at the end of that statement, ref. 17 supports the second half of it, but there's nothing about the proportion of the surface that was imaged, and the number 25% appears nowhere in that article. We need an additional source after "during the flyby missions". Renerpho (talk) 02:58, 1 July 2024 (UTC)
•  Fixed The source for the "peanut-shell" shape didn't actually support that claim. I've reworded that, added a better source, and have resolved a few minor c/e issues in the "Structure and composition" section. Renerpho (talk) 07:17, 6 July 2024 (UTC

Fixed problems in History section

General comments (fixed)

(None yet)

Before 1066 (fixed)

•  Fixed Ref.29 repeats the outrageous claim that Halley's comet was depicted in the 7th century, and it may actually be the original 1967 source for that idea. Galaxy Science Fiction is not a scientific publication, and has no place in this article. Renerpho (talk)
•  Fixed Ref.65 is a link to a Wikipedia article (Yanaikatchai Mantaran Cheral Irumporai) that is itself tagged as "needs additional citations for verification". That's doubly bad. Renerpho (talk) 19:07, 30 June 2024 (UTC)

  Compare the problem with what is now ref.145. Renerpho (talk) 08:40, 4 July 2024 (UTC)

•  Fixed The link in ref. 62 (BM 41462, London, British Museum) doesn't work, and I cannot find the correct page. This reference may need to be replaced. Renerpho (talk) 09:15, 4 July 2024 (UTC)

  The image appears all over the internet, but most of those obviously originate from the 2005 upload of the image to Wikipedia. The only version I can find in a scientific publication is in [11], p.4, from 2016, but I think that's also just a copy of the Wikipedia version. Renerpho (talk) 09:26, 4 July 2024 (UTC)

  I've found the original source (Walker, 1985). The British Museum website isn't needed. Renerpho (talk) 09:46, 4 July 2024 (UTC)

•  Fixed Quote: The 451 AD apparition was said to herald the defeat of Attila the Hun at the Battle of Chalons. -- It's so frustrating that we have to cite newspaper articles[12] for something like this, rather than a proper scholarly source. Not only because our citation wrongly calls this a New York Times article when it actually appeared in the Washington Post, but also because it's really hard to track down who said this, and exactly where. I thought for a moment that this was similar to the story about Genghis Khan in 1222, which turned out to be a legend, but there's more substance here. Our article Battle of the Catalaunian Plains mentions Comet Halley, but without a citation (why???). They say it was due to the entries of Hydatius' chronicle. The article does cite "Hydatius, Chronicon, 150" elsewhere. In The Battle of the Catalaunian Fields, 451 AD: Flavius Aetius, Attila the Hun, and the Transformation of Gaul, Evan Schultheis writes (§5, p.70): "When Attila arrived at Fontvannes on 18 June, early the following morning before dawn on 19 June was the first appearance of Halley’s Comet, an event recorded in both Chinese chroniclers and Hydatius which helps date the battle. The comet appeared in China on 9–10 June, while Hydatius states it appeared on the fourteenth Kalend of July (fourteen days before 2 July), and could be seen until early August. Thorismund officially succeeded Theodoric after its appearance, according to Hydatius." His source is "Hydatius, Continuatio Chronicorum, 151". That's enough to finally lead to Kronk's Cometography, Volume 4, p.82, which not only gives a really nice summary of the history of the computation of Halley's orbit, but also finally cites a complete source for the 451 AD sighting: "Hydatius, Continuatio Chronicorum Hieronymianorum (468), page 26 — Monumenta Germaniae Historica, Auctorum Antiquissimorum, volume 11, Theodorus Mommsen (ed.), Berlin, 1894." That's [13] p.26, v.151: "Stella cometes a XIIII. kal. Iulias apparere incipit, quae tertio kal. diluculo ab oriente visa post occasum solis ab occidua parte mox ecruitur. kal. Aug. a parte occidentis apparet." (A comet star begins to appear on the 14th kalend of July, which on the third kalend is seen in the early morning from the east, after the setting of the Sun on the west side it soon begins to fall. In kalend August it appears from the west side.) Why can none of the sources, not even Kronk, just give us the text, instead of their cryptically abbreviated references? Renerpho (talk) 19:04, 7 July 2024 (UTC)

  I will work on including this into the article later. I'll probably just cite Schultheis and Kronk, and remove the useless newspaper article. I cannot be bothered to resolve the citation issues in Battle of the Catalaunian Plains. Renerpho (talk) 19:04, 7 July 2024 (UTC)

  Done. Renerpho (talk) 21:16, 7 July 2024 (UTC)

1066 (fixed)

•  Fixed Ref.82 looks questionable to me. I am not sure if that source exists, or at least where to find it. A Google search for the title[14] gives two results: This Wikipedia article, and a deleted Reddit post. The Wikipedia article about the author, Lupus Protospatharius, doesn't list a work of that name. Renerpho (talk) 20:34, 29 June 2024 (UTC) Found it; the title given here was wrong. I'll replace the ref. Renerpho (talk) 20:46, 29 June 2024 (UTC)

1145–1378 (fixed)

•  Fixed There is now a ^[who?] tag in the 1145–1378 section. The source we have (a New York Times article) is insufficient. Renerpho (talk) 21:15, 30 June 2024 (UTC)

  Similarly to the BBC news article we had, the 1997 New York Times article is a case where something is claimed in a newspaper article, without indicating a source.

  The first mention of this that I can find is from 1985, D. J. Arneson's "Halley's Comet. A brief guide to comets"[15] whose author is neither a historian nor an astronomer. It spends a single sentence on Khan and the 1222 apparition.

  This is repeated with a little more detail in the 1986 Third World International, which mentions it in passing (this magazine is neither about astronomy, nor about history). It says that "Genghiz Khan is said to have halted his invasions of Eastern Asia on sighting Halley's comet in 1222 and change his course to unleash his fury on the Muslim world instead". This may be so (or not?), but who said it, and where?

  All the online sources about this are non-specific. There are mentions on the Science Museum website and on history.com, but both may relate back to our Wikipedia article. What we need is a scientific article from 1985 or earlier that references the primary source. Renerpho (talk) 21:36, 30 June 2024 (UTC)

  Cosmic Wonder: Halley's Comet and humankind appears to cite the original source but I'd have to buy it to find out. Serendi^podous 14:11, 1 July 2024 (UTC)

  @Serendipodous: I may be able to get my hands on that book, but I'd like to know what makes you believe that it leads to the original source before I try. This is a children's book, so finding any kind of references/citations would be unusual.[16] Renerpho (talk) 01:01, 5 July 2024 (UTC)

  I have a difficult time believing that a book with 40 pages, aimed at children 3-7 years old, says anything about the original source for why Genghis Khan didn't start a war in 1222... If it does then that's my kind of children's book, and the author can expect some fan mail from me. Renerpho (talk) 13:22, 5 July 2024 (UTC)

  Ah never mind. It doesn't seem any more informed than other sources. Basically, the story is, "Genghis khan saw a blue streak pointing west. He took it as his own personal star, and decided to turn his conquests westward." I have no idea where the original source is for this. Serendi^podous 17:04, 5 July 2024 (UTC)

  @Serendipodous: You've crushed my dreams. Thanks for going the extra mile and checking! Renerpho (talk) 17:52, 5 July 2024 (UTC)

  Move to "fixed" (thanks, Praemonitus!). Renerpho (talk) 15:04, 6 July 2024 (UTC)

•  Fixed This isn't so much about this article itself, but about a necessary update to another one. This does lead back to possible problems with the information we're citing here though: I have added some details about the 1301 apparition. One reason why that apparition is significant is because of the discovery by the art historian Roberta Olson of an image of the comet in a painting by Giotto, which is what inspired ESA to name their mission to the comet Giotto. The problem is that the Giotto Wikipedia article mentions the link to the painting, but it doesn't cite Olson's work; it doesn't mention that the discovery had just happened when the spacecraft was launched; and it doesn't explain how that discovery was announced in 1986, which is after the launch of Giotto. What was the spacecraft known as originally? There is no information at all about the timeline of the naming of the spacecraft. The article makes it sound as if it had been named around 1980, which would be anachronistic. Either that, or the timeline of the naming of the spacecraft, and/or the identification of the painting, were different than what Olson's 1986 publication, or the naming citation of asteroid (471301) Robertajmolson, suggest. Renerpho (talk) 14:34, 5 July 2024 (UTC)

  NASA Authorization for Fiscal Year 1982 establishes that the mission was called Giotto as early as 1981 or 1982. Renerpho (talk) 08:21, 7 July 2024 (UTC)

  I've found Olson's original publication, from 1979. Odd that it's apparently not referenced in the 1986 paper, but whatever. Renerpho (talk) 08:39, 7 July 2024 (UTC)

  Interestingly, Olson mentions the depiction of the comet of 684 AD, quote: "Three such 'portraits' of apparitions of Halley's Comet before Giotto's time have been identified. The earliest one represents the apparition of A.D. 684, although it was not executed until eight centuries after the fact, in the Liber Chronicorum, or Weltchronik, of Hartmann Schedel. known in English as the Nuremberg Chronicles because it was printed in Nuremberg." As mentioned above (Talk:Halley's Comet#684 CE depiction?), this idea was popular since the 1960s, but was disproven in 1989, ten years after Olson's paper. Renerpho (talk) 08:46, 7 July 2024 (UTC)

1835 (fixed)

•  Fixed Ref.101 is self-published, and the author is an expert in folklore, Fortean phenomena, and ufology, which doesn't make him more reliable for a claim about the history of astronomy. Surely there are better sources for the earliest photograph of the Moon than this? Renerpho (talk) 19:05, 29 June 2024 (UTC)

1910 (fixed)

•  Fixed I have replaced ref.105 by a more reliable source. Renerpho (talk) 21:00, 29 June 2024 (UTC)
•  Fixed Ref.106 came with very little information. I have expanded it as far as I can (and added a link to its Google Books page), but there is no page number, and I cannot find the thing that this is supposed to say in the book. This looks like a "failed verification" to me. Renerpho (talk) 21:09, 29 June 2024 (UTC)
•  Fixed Ref.107 just gives a link to an online library, which appears to be dead. The citation doesn't say anything about the actual source, just that it appears in the digital library of Paris Observatory; so digging up the original reference may be tricky. The URL has actually been archived,[17] but it includes nothing of interest, so this is another "failed verification". Renerpho (talk) 21:15, 29 June 2024 (UTC)
•  Fixed @Serendipodous: In this edit, you've removed the statement that Flammarion was misquoted, which had been tagged as needing a citation. The source[18] only says that the press reported him saying this. I don't think we can be sure that he actually did, or believed it. Or do you have another source, beyond "as far as I can tell, he did say this"? Renerpho (talk) 21:56, 29 June 2024 (UTC)

  See Camille_Flammarion#Halley's_Comet for Flammarion's actual statements about this. He didn't believe it, and was quite annoyed that the press reported that he did. Quote: "When astronomers announced that the Earth would pass through the tail of Halley's Comet in May 1910, Flammarion was widely reported, in numerous American newspapers, as believing that toxic gases in the tail might "snuff out all life on the planet". In fact, he said no such thing." Renerpho (talk) 22:06, 29 June 2024 (UTC)

  He definitely said such a thing. I have the quote from the book you cited (from audible, so no page number)

“Since comet tails range from 30 to 50 million km in length, it is clear that the tail might envelop us for several hours. What will be the result of this meeting, of such an immersion? There is no need to rehash the various ways a comet could snuff out life on Earth. What would be the point? From the mechanical, physical, chemical and thermodynamic viewpoint, we may at once acknowledge that we know nothing of the fate reserved for us next May. The poisoning of humanity by deleterious gases is improbable… Doubtless if the oxygen of the atmosphere combined with the hydrogen of the comet’s tail, it would mean universal death with short shrift. If on the contrary there resulted a diminution of the supply of nitrogen, the brain of every one of us would experience an unexpected sensation of physical activity, and the human race would come to a sudden end in a paroxysm of joy, universal delirium and madness. At bottom, probably overjoyed at its state. Carbonic oxide, on the contrary, on the contrary, would cause universal poisoning of the lungs.”

And in the conclusion: “Anxious minds have no reason to be tormented, uselessly too, by these prognostications. Comet it is true are immense, but they are so light, so rarified, that the terrestrial atmosphere is like lead in comparison.

So, was he misquoted, yes. But it was still a reckless and stupid thing for him to have said. Serendi^podous 21:04, 1 July 2024 (UTC)

•  Fixed I added the book by Goodrich, which already existed as a reference. The exact place in the source is on pages 64 and 83. I can't get it to display ^[103]p.64,83 or something of that sort. Renerpho (talk) 22:17, 29 June 2024 (UTC)

1986 (fixed)

•  Fixed Ref.126 appears to be a duplicate of Ref.125 (or a reprint of the same article in a different newspaper). Ref.126 leads to a dead URL, so I cannot check. Renerpho (talk)
•  Fixed Ref.127 is another reference to Galaxy Science Fiction. The information may be true, but since this is not a peer-reviewed source and the author appears to be a sci-fi author, not a scientist, it's probably not suitable as a source. Renerpho (talk)

After 1986 (fixed)

(None yet)

2061 (fixed)

(None yet)

Fixed problems in Apparitions section

•  Fixed In ref.14 (Odenwald, 1997), the author mentions "return cycles", giving the 1986 apparition the number 30.[19] I suppose that's counting the apparitions, starting with the 240 BC apparition as number 1, but is this common enough that we should adopt it? If not then it may be a good idea to at least explain it, because the source is confusing without that information. The table of apparitions lends itself nicely to a column that gives the number. Renerpho (talk) 12:24, 4 July 2024 (UTC)

  I have amended the table accordingly. Renerpho (talk) 12:32, 4 July 2024 (UTC)

  And when a reliable source is found mentioning an even earlier return, will we then renumber the "return cycles"? This sounds like a silly idea unless a better source can be found for this number -- a much more logical choice would be numbering predicted returns (1 = 1759, 2 = 1835, etc. and giving negative numbers to the earlier returns). AstroLynx (talk) 15:38, 4 July 2024 (UTC)

  @AstroLynx: I have no experience with this numbering system in astronomy, having never encountered it before, but I see no issue with using negative numbers if it became necessary. In genealogy, generations are commonly numbered this way, and the discovery of earlier ancestors is a common "problem" for genealogists. To quote from [20], which is just one example: "The standard notation in genealogical books to trace the descendants of a certain person is to assign a generation number 1 to him, generation number 2 to his children, 3 to his grandchildren, and so on. [...] their antecedents, generations −1, −2, −3,... , in ascending order. [...] In studying history we arbitrarily fix the birth of Christ as the origin and number the later centuries 100 A.D., 200 A.D., and so on, and the earlier centuries are 100 B.C., 200 B.C., and so on. The negative numbers of generations behave exactly like B.C. dates and are used in calculations the same way". So, I suppose a hypothetical earlier apparition around 315 BC would receive the number -1 by that logic. Note also that there is no year 0 in the common system (the year 1 BC was followed directly by 1 AD). Renerpho (talk) 00:24, 5 July 2024 (UTC)

  The only place in astronomy that comes to my mind that does something like this is with solar cycles. The problem of having to number earlier cycles doesn't arise there, because cycles prior to the official start of the count in 1755 are not well defined, due to the Maunder Minimum. Renerpho (talk) 00:31, 5 July 2024 (UTC)

  A survey of orbital studies on 1P/Halley in the ADS website suggests that only two numbering systems appear to have been used in the astronomical literature:

  Kamieński equated n = 0 with the 837 return.

  Kiang, Zhang, Broughton and Wang & Gong all equated n = 0 with the 1986 return.

  Perhaps it is best to use the latter system as it is adequately sourced. AstroLynx (talk) 14:43, 5 July 2024 (UTC)

  Thanks for surveying the literature! This does suggest that putting 0 at the 1986 apparition is the most common, and that 1910 should be -1, 1835 should be -2, etc. It is also the easiest to explain, even if the negative numbers may look a bit awkward. The table in Zhang, p.122, seems the most complete to me. Broughton's table only goes back to the apparition of 12 BC, while Wang&Gong's table leaves out the 1986 apparition, and looks like a less complete version of Zhang's. If nobody objects, I would edit the article accordingly, with Zhang as the source for the numbering. Renerpho (talk) 15:00, 5 July 2024 (UTC)

  @AstroLynx: Zhang also lists dates for the perihelion dates of each apparition, and they clearly note which calendar they're talking about and what the Julian day is supposed to be in each case. Sadly, their orbit computations appear to be older than, and inferior to, the ones we're citing in the apparitions table; otherwise this could have helped solve the problem noted above about the date of the 1607 perihelion (compare my comment from 23:04, 30 June 2024). Zhang gives it as 27 September 1607, Gregorian calendar. Renerpho (talk) 15:08, 5 July 2024 (UTC)

  I've changed the table of apparitions accordingly. Renerpho (talk) 15:40, 5 July 2024 (UTC)

•  Fixed Ref.145 is incomplete as well. This is most likely S. Milbrath's Star Gods of the Maya, which isn't in the bibliography. And a page number would be nice... Renerpho (talk) 20:19, 29 June 2024 (UTC)

  It still needs a page number. Renerpho (talk) 02:17, 1 July 2024 (UTC)

   Done, insofar as it is now tagged with . This is now ref. 146. Renerpho (talk) 08:40, 4 July 2024 (UTC)

  A page number has been added. Renerpho (talk) 15:04, 6 July 2024 (UTC)

•  Fixed Ref.144 is incomplete. This is just a claim that would need a [citation needed] tag if it appeared anywhere else in the article. Renerpho (talk)

  I'm not sure what you're asking me to do to ref 144 (now ref 140). The link in ref 107 works fine for me; the fact it states is corroborated. I'm just not sure how to cite it. Serendi^podous 21:21, 29 June 2024 (UTC)

  @Serendipodous: The ref.144 I mentioned is now ref.137 ("The poets Kurunkozhiyur Kizhaar and Koodaloor Kizhaar..."). If the link in ref.107 works for you then that's great. What does it lead to? Renerpho (talk) 21:30, 29 June 2024 (UTC)

  Yanaikatchai Mantaran Cheral Irumporai does cite it, but I don't understand the citation format used in that article. Renerpho (talk) 21:33, 29 June 2024 (UTC)

  Ref 107 is just a picture of an ad featuring Halley's comet, which is all the text says. Serendi^podous 21:35, 29 June 2024 (UTC)

  Thanks. The Sangam literature of Ancient Tamils needed for ref.137 isn't known to Google Books. Any other idea where to find it? Renerpho (talk) 21:38, 29 June 2024 (UTC)

  I don't think it's a book; I think the cite is directly quoting the Sangam literature of ancient Tamils. Serendi^podous 21:41, 29 June 2024 (UTC)

  Okay. Maybe the citation makes sense to someone who knows about that field, but to me, it is quite vague. Maybe Purananuru leads to the actual location? Renerpho (talk) 21:44, 29 June 2024 (UTC)

  I think [21] includes the quote needed. A Google Books search for an excerpt of the quote gives that book as the only result.[22] Sadly the search inside the book doesn't work. Renerpho (talk) 21:48, 29 June 2024 (UTC)

  The link in ref 107 works fine for me; the fact it states is corroborated. I'm just not sure how to cite it. I redid the citation, per the format that's suggested on the source page (which is now working for me). Renerpho (talk) 22:28, 29 June 2024 (UTC)

I have turned the reference to the part from Sangam literature into a note, and tagged it as . This has always been more of a note than a reference anyway. Renerpho (talk) 14:51, 5 July 2024 (UTC)

The story in the Purananuru can be read in full detail here -- however, the description clearly suggests a meteor, not a comet. Nor is the year 141 AD mentioned in this account. I suggest deleting it. AstroLynx (talk) 12:06, 7 July 2024 (UTC)

Oh dear... Agreed. Thanks, AstroLynx! How do such things end up in articles about comets? Renerpho (talk) 12:10, 7 July 2024 (UTC)

Images

•  Fixed Is it just me, or does the article look cluttered? There are a lot of images, and many look either unnecessary, or not well-placed. Renerpho (talk) 22:12, 29 June 2024 (UTC)

  Yes there is some image clutter in the History section. I'm not sure that some of those images add a lot of value. Praemonitus (talk) 18:42, 30 June 2024 (UTC)

  @Praemonitus: I've reworked the image placement and selection. What do you think? Renerpho (talk) 21:00, 30 June 2024 (UTC)

  @Renerpho: Okay I guess. The {{Multiple image}} template could be used for combining multiple images vertically. Praemonitus (talk) 03:39, 1 July 2024 (UTC)

  @Praemonitus: Good idea, thank you! I've done a bit of an editing marathon (70 edits and lots of reading over the last 8 hours), and I'm about to sign off. There were quite a few issues that I've been able to fix. I have started to go through the references one by one. Having looked at about a third of them already, there are some issues where a solution isn't straightforward, or where I'm not sure what to do; those are now marked as  Pending (or as  Fixed if they've since been solved). I have summarized some of the journal articles I've read that are not yet used as references, but which may become helpful. I'll see if I can pick up tomorrow from where ever the article stands then. Renerpho (talk) 03:46, 1 July 2024 (UTC)

  @Praemonitus: I have combined some of the images with the multi-image template, as you suggested. I'm not sure this is the best possible solution. Do you have an idea how to better arrange them? Renerpho (talk) 09:28, 4 July 2024 (UTC)

  @Renerpho: they seem fine to me. The "Illustrations of prior comet appearances in the January 1910 Popular Science Monthly magazine" gallery seems a little clunky; it might be better as a vertical "multiple image". Praemonitus (talk) 13:45, 4 July 2024 (UTC)

  Done. Renerpho (talk) 05:43, 5 July 2024 (UTC)

  @Praemonitus: I think this is better. I've also decided to rotate the images, so they fit better vertically. Renerpho (talk) 13:23, 5 July 2024 (UTC)

  @Renerpho: that works. Praemonitus (talk) 20:00, 5 July 2024 (UTC)

Shortened footnote template

The article is citing sources in the bibliography, but is doing so inconsistently. I'd like to convert those to use the {{sfn}} template. Does anybody object? Praemonitus (talk) 18:39, 30 June 2024 (UTC)

I don't object. There are a number of sources that can be moved from the references to the bibliography section. Goodrich is one example (maybe that gets rid of the problem I mentioned above, 22:17, 29 June 2024). Milbrath's book is also better handled that way, and maybe a few others that I'm missing. Renerpho (talk) 18:57, 30 June 2024 (UTC)

 Fixed Renerpho (talk) 07:03, 6 July 2024 (UTC)

To be done

I am moving the remaining issues down here, to keep the growing list a bit more manageable. Renerpho (talk) 12:00, 4 July 2024 (UTC)

I haved checked the following sections for problems: Renerpho (talk) 07:07, 7 July 2024 (UTC)

• Lede:  Done
• Computation of orbit:  Done
• Orbit and origin:  Done
• Structure and composition:  Done
• History:  Not done
• Apparitions:  Not done

WP:MOS issues

•  Pending Our references "kronk", "Kronk2009", and cometography.com can all be combined into one if we just keep "Kronk2009" (with appropriate page numbers), which then could be put into the bibliography. Renerpho (talk) 21:40, 7 July 2024 (UTC)

Problems in lede section

•  Pending Quote: During its 1986 visit to the inner Solar System, Halley's Comet became the first comet to be observed in detail by spacecraft, providing the first observational data on the structure of a comet nucleus and the mechanism of coma and tail formation. This currently has two citations. Is it really so controversial that we need to cite two sources in the lede? Do we need a citation at all? Renerpho (talk) 05:49, 7 July 2024 (UTC)
•  Pending Quote: appearing every 75–79 years I understand why we may need a citation for this, since it's factually wrong. If we have to cite something then do we really have to contradict ourselves within the citation ("1P/Halley Orbit". Minor Planet Center. Archived from the original on 4 July 2022. Retrieved 28 June 2022. (epoch 451 is 79.29 years)? Also, we make it sound as if epoch 451 was an exception. It is not: According to that reference, epoch 295 is 79.13 years, epoch 1066 is 79.26 years, epoch 1145 is 79.02 years, epoch 1222 is 79.12 years, and epoch 1301 is 79.14 years. Compare the same problem raised again in Problems in Orbit and origin section (with a different reference and slightly different numbers).
  Do we need the other citation, for is consistently visible to the naked eye from Earth? The only reason I can think of why this may be challenged is a misinterpretation of the word consistently, and if that's the issue then maybe we should rephrase it. Renerpho (talk) 05:49, 7 July 2024 (UTC)

  Thinking about the previous one, the source may not actually support what we're saying. The difference is subtle; to quote our source:[23] Among those comets that can be seen easily with the naked eye, Comet Halley, with an average period of 76 years, is the only one that returns in a single lifetime. Our version isn't quite the same. For example, comet 12P/Pons-Brooks reached +3 mag in 1884, +6 mag in 1954,[24] and was visible to the naked eye again this year, at +4 mag.[25] There is a difference between "easy" and "consistent". What the article is saying right now is better than the version that was featured on the Main Page in 2010 ("the only naked-eye comet that might appear twice in a human lifetime"), which may just be wrong, but I think it's still not great... Renerpho (talk) 08:21, 8 July 2024 (UTC)

Problems in Computation of orbit section

•  Pending Quote: Although he had suspected that two comets that had appeared in succession in 1680 and 1681 were the same comet before and after passing behind the Sun (he was later found to be correct; see Newton's Comet),^[23] he was unable to completely reconcile comets into his model. -- The source says that it was Flamsted who suspected them to be the same comet, and that the possibility hadn't occurred to Newton until Flamsted told him about it. We currently don't acknowledge Flamsted's contribution. The article we link to about Newton's Comet doesn't actually mention Newton until the final paragraph, where it has the following to say about it: Isaac Newton used the comet to test and verify Kepler's laws. John Flamsteed was the first to propose that the two bright comets of 1680–1681 were the same comet, one traveling inbound to the Sun and the other outbound, and Newton originally disputed this. Newton later changed his mind, and then, with Edmond Halley's help, purloined some of Flamsteed's data to verify this was the case without giving Flamsteed credit. Why should we follow his example? It's a pity that the article about that comet doesn't acknowledge that Newton was the last person on Earth who actually saw it with their own eyes (Lancaster-Brown, p.36), based on predictions he had made using his own model. Oh well, we have enough work to do with Halley's Comet!
  What is our source for the second part (that Newton was unable to reconcile comets into his model)? The source we use for the first part doesn't seem to say so. Renerpho (talk) 06:16, 7 July 2024 (UTC)
•  Pending Quote: a period that has since been found to vary between 74 and 79 years -- The problems with that statement are already discussed elsewhere, compare "Problems in lede section" and "Problems in Orbit and origin section" (the period often gets larger than 79 years). Renerpho (talk) 06:25, 7 July 2024 (UTC)
•  Pending Quote: The confirmation of the comet's return was the first time anything other than planets had been shown to orbit the Sun. There is no reference for this, and the reference for the following sentence (Hughes, The History of Halley's Comet) doesn't seem to say so. Renerpho (talk) 06:37, 7 July 2024 (UTC)
•  Pending Walker (1985), currently ref. 64, goes into a bit of detail about the description in the Chinese chronicle from 240 BC. Apparently, that discovery was first announced in a French journal in 1846, and Walker notes that the 1984 (re)discovery of the Babylonian tablets "represents the first significant addition to our knowledge of the past history of the comet since the French publication of Chinese observations in 1846". The problem is that the Wikipedia article Records of the Grand Historian doesn't mention that 1846 paper, or what Walker's reference is about. The Chinese work was known before 1846, so what is it that was discovered that year? I cannot find the source. Stephenson doesn't provide any details either. Something important was published about Halley's comet in 1846 (likely important enough that we have to mention it), but I have no idea what it is. Renerpho (talk) 11:15, 4 July 2024 (UTC)

  The 1846 catalogue is probably that of Édouard Biot, "Recherches faites dans la grande collection des Historiens de la Chine, sur les anciennes apparitions de la Comète de Halley", Connaissance des Temps ou des mouvements célestes a l'usage des astronomes et des navigateurs pour l'an 1846 (Paris: Bachelier, 1843), Additions, pp. 69--84. Note that the actual year of publication was 1843! AstroLynx (talk) 15:29, 5 July 2024 (UTC)

  Biot's catalogue was supplemented a few years later by Paul-Auguste-Ernest Laugier, "Mémoire sur quelques anciennes apparitions de la comète de Halley, inconnues jusqu’ici”, Comptes rendus hebdomadaires des séances de l’Académie des sciences, 23 (1846), 183-189. AstroLynx (talk) 15:56, 5 July 2024 (UTC)

  @AstroLynx: Nice finds! I think Walker&Stephenson may be referring to either of those, or (more likely) both of them together. Interestingly, the last two apparitions listed by Biot are from 12 AD and 64 BC, which don't actually belong to Halley's Comet (he misidentifies them), and the paper stops two orbits short of the 240 BC apparition that I was expecting. Walker&Stephenson never explicitly say that the 1846 publication was about that apparition, and looking at what appears to have been known in 1843/1846, it's clear why: They couldn't even tell which sighting from that era belonged to Comet Halley, and Biot acknowledges that. He isn't certain about many of the slightly more recent apparitions (from the 1st millennium AD), and he lists several possible identifications for each of them (apart from the apparition of -86 BC, he always actually includes what we now know was Halley). Both works together should probably be mentioned in the section about the Halley's_Comet#Computation_of_orbit. Renerpho (talk) 16:08, 5 July 2024 (UTC)

  The 87 BC & 240 BC returns of 1P/Halley were actually first linked with Chinese observations in Cowell & Crommelin (1908). AstroLynx (talk) 16:25, 5 July 2024 (UTC)

  This was the last paper in a series of important papers (Paper I, Paper II, Paper III, Paper IV, Paper V), not mentioned in the bibliography, on the evolution of the orbit of 1P/Halley accounting for the gravitational perturbations of the planets Venus to Neptune. AstroLynx (talk)

  Nice how that starts to form a coherent picture. And it's material for the article, 100%. There are a few questions:

  I'm curious if Walter&Stephenson were unaware of Cowell&Crommelin, or if they didn't consider their work interesting enough. It seems strange to call a link to an observation from 164 BC the most significant addition since 1846, when there's a 1908(!) paper that linked observations from 87 BC and 240 BC!

  Two quotes from Cowell&Crommelin: "Going back another round, the date B.C. 239 January was found; we think it not unlikely that the comet observed in the spring of B.C. 240 was Halley's." -- indeed. And: "It appears worth while to calculate the three revolutions B.C. 12 to B.C. 240 by more exact methods, and we hope to undertake this at a later date." -- Did they ever do so? If not, who did, and when was the link to the 240 BC observation made definitive? Surely, a much more accurate orbit could have been calculated once the comet was recovered a year later?

  There's this sentence in the article (at the end of the "Computation of orbit" section) that's very odd, in the context of the new information: Researchers in 1981 attempting to calculate the past orbits of Halley by numerical integration starting from accurate observations in the seventeenth and eighteenth centuries could not produce accurate results further back than 837 owing to a close approach to Earth in that year. It was necessary to use ancient Chinese comet observations to constrain their calculations. The source for this is Stephenson (1985). I mean, it's not wrong, but if the previous relevant paragraph ends with the situation in 1759, it's disingenuous, even misleading. Such calculations were successfully done in the mid-19th century, with the help of Chinese records. Advancements were made, both in the early 20th century and by Stephenson, but the approach wasn't original. Renerpho (talk) 17:02, 5 July 2024 (UTC)

  @AstroLynx: Paper I's introduction is insightful. It mentions an 1829 paper by Pontécoulant that established the orbital perturbations back to 1531; then one by John Russell Hind from 1850,[26] based on Chinese observations, which they say linked the orbit back to around 451. Laugier's work is mentioned, too, so Cowell&Crommelin were aware of his work (and, in turn, of Biot's), and used his approach for their study, especially when it came to the 451 and 760 apparitions (again with the use of Chinese records).
  Paper II starts by saying that they had linked the apparition of 1301 in Paper I, and were going to use Hind's approximation of the 1222 apparition to link that one.
  Paper III is spent on the time between 1066 and 1301, ultimately finding the date of the perihelion passage in 1066.
  Using that date, and Hind's approximation for the 989 apparition, they spent paper IV to compute the perturbations between 760 and 1066. Renerpho (talk) 20:38, 5 July 2024 (UTC)

  Pontécoulant's 1829 paper (actually from 1835) cited by C&C appears to be this one. A later paper is "Notice sur la comète de Halley et ses apparitions successives de 1531 à 1910", Comptes rendus hebdomadaires des séances de l’Académie des sciences, 58 (1864), 706-709. AstroLynx (talk) 21:48, 5 July 2024 (UTC)

  @AstroLynx: On p.71, Pontécoulant writes that "on verra au contraire dans ce mémoire que les résultats que j'ai rendus publics pour la première fois en 1829, n'ont subi depuis cette époque aucune altération importante" (On the contrary, this report shows that the results I first published in 1829 have not undergone any significant change since that time). The 1835 paper clearly isn't the one that Hind refers to. It doesn't talk about the 1531 apparition at all... Renerpho (talk) 22:14, 5 July 2024 (UTC)

  The 1835 book doesn't seem to give a source for this, but the 1864 book does. See the note on p.769: "Tous les détails du calcul sont rapportés dans le Mémoire de 1829 cité précédemment et qui a été inséré dans les Mémoires de l'Académie des Sciences, Recueil des Savants étrangers, t. VI, 2^e série. Les seuls changements qu'aient subis les résultats sont ceux qui proviennent des corrections qu'ont éprouvées depuis cette époque les masses planétaires et de quelques légères erreurs de détail que la révision de mes calculs m'a permis de faire disparaître." (All the details of the calculation are given in the Memoire of 1829 quoted above, which has been inserted in the Memoirs of the Academy of Sciences, Foreign Scholars, volume 6, number 2. The only changes to the results are those resulting from the corrections made to the planetary masses since that time, and from a few slight errors of detail which the revision of my calculations has enabled me to eliminate.) Renerpho (talk) 22:21, 5 July 2024 (UTC)

  Actually, the 1835 book gives a citation of sorts, on p.72, with some interesting background: "Je rappellerai ce qu'on lit sur ce sujet dans les Mémoires de l'Académie dcs Sciences, à la suite de l'annonce du prix proposé pour 1786, sur le calcul des perturbations de la comète de 1532. "On voit avecquelle suite l'Académie s'est occupée de cette grande question, jusqu'ici sans utilité bien apparente, mais dont la solution est du moins une des preuves les plus brillantes de la hardiesse et des forces de l'esprit humain. On permet aux compagnies savantes comme aux corps politiques, de songer quelquesois à la splendeur de l'empire, et avec d'autant plus de raison que dans les sciences cette splendeur ne s'achète jamais aux dépens du bien général, et que si les questions qu'on y propose ne sont souvent que curieuses, les méthodes inventées pour les résoudre, finissent presque toujours par avoir une utilité réelle." (Memoires de l'Académie des Sciences, Savans étrangers, tome X.)"
  (I would like to recall what we read on this subject in the Academy of Sciences, following the announcement of the prize proposed in 1786, on the calculation of the perturbations of the comet of 1532. "We see with what continuity the Academy has occupied itself with this great question, hitherto of no apparent use, but whose solution is at least one of the most brilliant proofs of the boldness and strength of the human mind. Learned societies, like political bodies, are allowed to think for a few moments of the splendor of the empire, and with all the more reason that in the sciences this splendor is never bought at the expense of the general good, and that if the questions proposed are often only curious, the methods invented to solve them almost always end up having a real utility." (Memoires de l'Académie des Sciences, Savans étrangers, volume 10.) Renerpho (talk) 22:40, 5 July 2024 (UTC)

  So... there was a prize since 1786, for the first one who calculates the perturbations for the 1531 apparition! And I guess Pontécoulant claimed that prize in 1829. What was that prize about, where was it announced, and did Pontécoulant actually "win"? Another mystery to solve. Renerpho (talk) 22:45, 5 July 2024 (UTC)

  The 1786 prize seems to refer to the Great Comet of 1532, not the return of Halley's Comet in 1531. AstroLynx (talk) 23:05, 5 July 2024 (UTC)

  @AstroLynx: Oh? Could that mean Cowell&Crommelin were wrong when they credited Pontécoulant with linking Halley's 1531 apparition? That seems like a real possibility. Renerpho (talk) 23:30, 5 July 2024 (UTC)

  Um, [27] says that the Great Comet of 1532 was, in fact, Halley's comet. This cannot be right though, compare [28]. Renerpho (talk) 23:32, 5 July 2024 (UTC)

  Pontécoulant's detailed 1829 paper (published in 1835) appears to be this one. The other paper published in 1835 appears to be only a summary. AstroLynx (talk) 22:53, 5 July 2024 (UTC)

  @AstroLynx: Maybe. Considering the later references, I find it surprising that the 1531 apparition isn't mentioned anywhere in that paper, so something is amiss. That paper does some laborious manual integrations though, and comparing the orbital elements he gets for the 1682, 1759 and 1835 apparitions, they closely match the modern values (at least as far as I can tell; his reference frame doesn't match the modern J2000, though I cannot easily compare the angles). I am currently translating the reference to 1786 on p.947... Renerpho (talk) 23:14, 5 July 2024 (UTC)

  It says: "The conditions of the prize proposed by the Academy for 1826 and successively awarded for 1827 and 1829, required competitors to apply the formulas relating to comet perturbations, not only to the determination of the next return of the comet of 1759, but also to the motion of one of the two other periodic comets whose return has now been established. In order to comply with these conditions, I had already calculated the perturbations of the periodic comet of 1819, from that time until 1827, but I thought it necessary to delete this part of my Memoire, which has become unnecessary due to the great work published by Mr. Encke on the perturbations of this comet, from its first appearance in 1786, until the present time."
  Pontécoulant is referring here to 2P/Encke, which first appeared in 1786, and was seen again by Encke in 1819. I'm not sure if Pontécoulant is referring to the same prize as before, or a related one... Renerpho (talk) 23:24, 5 July 2024 (UTC)

  Some interesting points from Hind's paper:

  • He credits Pingré's Cometographie ([29], published in 1783) with making the link to the 1456 apparition, with two definitive observations listed by Pingré (one from Austria, one from Italy).
  • He notes that Halley had conjectured that the apparition before that had happened in 1380, but that Laugier has shown that it happened in 1378, and was very similar to the circumstances in 1835. Chinese records were crucial for that link.
  • Hind refers to a second, earlier paper by Laugier, in the Connaissance des Temps, also from 1846.

  Laugier's pubications in CdT for 1846 are here and here. AstroLynx (talk) 21:26, 5 July 2024 (UTC)

  • Edouard Biot is credited for compiling the observations from China, including those by Ma Duanlin, while Hind himself compiled observations by Pingré, Hevelius, and Lubieniecki. Biot is also credited for his publication in the appendix to the Connaissance des Temps from 1846, which was the basis for Hind's computations about the possible link to the comet of 11 BC. Hind is fairly certain that he has linked Halley to that comet (and in hindsight, he's correct). Renerpho (talk) 21:08, 5 July 2024 (UTC)

  A few things have become clear to me:

  1. Our section about the computation of Halley's orbit is very incomplete. There's a really interesting story of scientific discovery and collaboration, and it's a shame we haven't been telling it. I'm looking forward to putting this together, but we should clearly establish the timeline before we start writing.
  2. Claims about who linked a certain apparition are dubious. Those links aren't made by individuals, but are a process, from conjecture to various degrees of certainty, and leading to a general consensus. This can take decades, like with the link to the apparition of 11/12 BC. (Question: Did anyone between 1850 and 1907 do some significant work on that link?)
  3. Turning this around, just because someone claims that they are "fairly certain" they can link an observation doesn't mean they actually have. Cowell&Crommelin wouldn't be so excited(?) about definitively linking the 12 BC comet if they had considered Hind's work on it definitive. On the other hand, Cowell&Crommelin are also quite certain they have linked the 240 BC observations, but so far, I haven't seen where that link has actually been shown to be valid.
  4. The claim of a link to Greek observations in 466-467 BC,[30] noted to be WP:FRINGE down below, may well fall into the early stages of this process. I don't know whether we should treat the claim as such, or continue to ignore it, even with a handful of reliable sourcing referencing it. Renerpho (talk) 21:26, 5 July 2024 (UTC)

  About 2.: Ravene (1897)[31] worked on the 141 AD apparition, building upon the works of Pingré and Hind. Ravene notes that Hind had found observations from 141 AD in Chinese records, but had not provided orbital elements for that epoch. Ravene adds newly found records from India that substantiate the link, and deduces orbital elements. Ravene does not mention the apparition of 11/12 BC. Renerpho (talk) 04:52, 7 July 2024 (UTC)

  @AstroLynx: Laugier's pubications in CdT for 1846 are here and here. Thanks again! The 1st one is about 1301, the 2nd one about 1378. In the 2nd one, Laugier mentions Pingré and his link of the 1456 apparition (including the observations from Austria and Italy that Hind later referred to). He also notes that Pingré in 1783 was unaware of the Chinese records, which I find interesting (even though it's not surprising). An interesting quote (p.101, my translation): "The comet's small distance from the Earth in 1378 must have produced disturbances that could account in part for this one-and-a-half-year difference in the average length of its revolution." Halley came within about 0.18 AU of Earth that year, not enough to cause any significant changes. I don't know what caused the perturbations he mentioned, but Laugier was wrong. I'll have to read the paper about the 1301 apparition to see if he goes into it there, and maybe corrects himself. Renerpho (talk) 10:33, 6 July 2024 (UTC)

  The 1st one, the paper about the 1301 apparition, is short, but it is a treasure-trove. To summarize: Lagier believed in 1846 that Richard Dunthorne was aware in 1751 of observations of Halley's Comet from 1301, both from a manuscript kept at the Cambridge library and from Chinese observations, and that Dunthorne would probably have linked the 1301 comet to Halley's if he hadn't misinterpreted those records. Pingré in 1783 was troubled by the same problem. Laugier's contribution was to regognize that error, after which everything else falls into place. Renerpho (talk)

  Dunthorne (1751) mentions several comets, including the one of 1301, but does not mention Chinese observations. If the JSTOR download link doesn't work, try pasting the url or doi number in sci-hub. AstroLynx (talk) 14:35, 6 July 2024 (UTC)

  Interesting. As I said below, I am not sure how to interpret Laugier's accounts. The possibilities range from my translation being wrong, over me just misunderstanding what he meant, to Laugier having been in error. Two of these are likely; the other is not. Renerpho (talk) 04:55, 7 July 2024 (UTC)

  I am a bit confused by this. Is there any way how Dunthorne could have had access to the Chinese records, prior to the work of Biot? Is Laugier mistaken, or am I just completely misunderstanding what he's saying?

  Laugier writes: "Having noted the resemblance of four of the elements of the comet which I calculated in 1842 with those given by Pingré for the comet of 1301, I was led to examine what confidence could be placed in the calculations relating to this ancient comet. Recognizing that the apparent trajectory resulting from Pingré's orbit deviates considerably from the route indicated by the Chinese and by the observations in the Cambridge manuscript, I thought it necessary to resume the calculation of the elements of the comet of 1301. This calculation is based almost entirely on the observations made in China since September 16, 1301, recorded in a memoir by Mr. Biot, and on the following positions, taken by the Cambridge astronomers on September 30 and October 6, 1301, and reported by Dunthorne in the Transactions philosophiques, volume 47 (1751-1752), page 285." This is followed by the two observations that Dunthorne had found in a manuscript at the Cambridge library.

  The citation is clarified by Kronk's Catalog of Unconfirmed Comets, volume 1,[32] which more correctly cites "R. Dunthorne, Philosophical Transactions of the Royal Society, 10 (1751), p.285", in which Dunthorne discusses an attempt by Halley to link together the two comets of 1264 and 1556, predicting a return in 1848 (Kronk, p.97).

  I don't know if the Philosophical Transactions are available online. I haven't found them. Being unable to read Dunthorne's letter in full, I don't know what exactly he wrote about the comet of 1301. Laugier gives a hint in his footnote, remarking on an apparent error in Dunthorne's calculations: "We can be convinced, from the march of the comet observed in China, that the latitude of September 30 is indeed 26 degrees, as indicated in a manuscript deposited in the library of Cambridge College, and not 16 degrees, as Dunthorne would seem to believe, in a note appended to his letter."

  That same error would later be repeated by Pingré. After listing the very different orbital elements that result from those two alternatives (26 versus 16 degrees), Laugier continues: "Such an enormous dissimilarity will no doubt come as a surprise. Pingré, it is true, gave his elements as very uncertain, and showed how much trouble they had cost him when he ended the chapter on this comet with this sentence: 'I have searched in vain for a more precise theory; the English observers of those remote centuries [those who wrote the Cambridge manuscript; ed.] were no Newtons, Halleys or Bradleys: I can only repeat that their observations have been rescued from oblivion in order to torture overzealous calculators.'"

  "In any case, I have calculated a series of positions occupied by the comet, resulting in an apparent trajectory that satisfies, in every detail, all the indications I have been able to gather (see Mr. Biot's memoir, page 46). By going back to the appreciations that guided Pingré in his calculations, and by scrupulously analyzing the various writings of historians, we can find the cause of his error. Firstly, he misinterpreted the Chinese texts to mean that the comet had an austral latitude on September 16, 1301. As a result, he was forced to reject the very precise observations in the Cambridge manuscript. On the contrary, it can be seen that, taken in their true sense, all these observations agree with each other in a remarkable way." Renerpho (talk) 12:24, 6 July 2024 (UTC)

  Yeomans (1986), pages 65-68[33] gives a great summary of the history, from the 1780s to the early 1980s, ending with Yeomans' definitive link of the 240 BC observations in 1981. I think this is the perfect source for our article, and with it, we could be in a position to actually start writing... Renerpho (talk) 14:42, 7 July 2024 (UTC)

  It's funny how Historical comet observations in China#Halley's Comet goes into more detail about this than the main article. There are some useful references in that article though! Renerpho (talk) 17:06, 7 July 2024 (UTC)

  Kronk's Cometography, Volume 4, p.82 gives another nice summary of the history of the comet, its orbit computation, and sightings. Renerpho (talk) 21:20, 7 July 2024 (UTC)

Problems in Orbit and origin section

•  Pending In Halley's Comet#Orbit and origin, we define Jupiter-family comets (JFCs), saying that Most short-period comets (those with orbital periods shorter than 20 years and inclinations of 20–30 degrees or less) are called Jupiter-family comets. This is rather unclear, leaving the question why most (but not all?) such comets are called JFCs. On the other hand, I suppose it may be worded vaguely on purpose. We could change it to the definition used in Jupiter-family comet, but a citation would be needed for that definition.
  There are two references given for the definition (P<20y, i<30°) in the Jupiter-family comet article: One is a dead link, but was archived close to the access date.[34] The other one is [35]. Neither of them support what the article is saying, particularly about the i<30° criterion. Our reference Morbidelli (2005),[36] used for the sentence immediately following, doesn't support it either, but gives a different definition based on Tisserand's criterion, distinguishing Jupiter-family from Halley-type comets by $2<T_{J}<3$ for JFCs vs. $T_{J}<2$ for Halley-type comets. We definitely need a source that connects this to the threshold of i<30°, as the sentence quoted above is currently unreferenced.
  Note the lack of any restrictions on the orbital period; P<20y is not a requirement for being a JFC, and neither is i<30° (and there are exceptions for both).
  There is a second problem with the statistic in the preceding sentence (Periodic comets have an average inclination to the ecliptic of only ten degrees, and an orbital period of just 6.5 years), which is based on a 1985 paper and may no longer reflect current knowledge, but the definition of JFC is of more immediate concern. Renerpho (talk) 18:57, 5 July 2024 (UTC)

  Some quotes from Morbidelli:
  "Because the Tisserand parameter remains close to 3, the inclination cannot grow to large values (the growth of i would decrease T). So, the final inclination distribution is comparable to the inclination distribution in the scattered disk, i.e. mostly confined within 30 degrees." I suppose this would work for the i<30° part. Also:
  "Historically, the partition between the two classes is done according to the orbital period being respectively longer or shorter than 20 y. This threshold has been chosen because there is an evident change in the inclination distribution at the corresponding value of semi-major axis (see Fig. 12). However, comets continuously change semi-major axis as a consequence of their encounters with the planets. [...] Thus, by adopting a partition between Halley-type and Jupiter family comets based on orbital period, one is confronted with the unpleasant situation of objects changing their classification during their lifetime."
  What is the reason to refer to an obsolete definition in either of our articles, and where does the additional restriction of i>20° come from? Renerpho (talk) 19:17, 5 July 2024 (UTC)

•  Pending In Halley's Comet#Orbit and origin, we say that these studies showed that its dynamics were chaotic and unpredictable on long timescales, but only a single study is cited. Where are the other ones? Two sentence further down, it's these studies also showed that many physical properties [...], with a different source. Do those two belong together? If so, why does the 2nd one appear only now? Does the phrase "these studies" even refer to the same studies in both cases?
  Does the sentence Halley's projected lifetime could be as long as 10 million years refer to its dynamical lifetime (how long it may take before it is ejected from its current orbit), as the context of where it is placed within that paragraph may suggest, or to its physical lifetime (the time until it is expected to evaporate), as the rest of the paragraph? Why is there no source for this sentence?
  What is These studies also showed that many physical properties of Halley's Comet dynamics can be approximately described by a simple symplectic map, known as the Kepler map supposed to mean, and what makes those maps simple (symplectic map doesn't say so)? And again, which studies are supposed to be the reference -- the one cited at the end of that sentence, or the studies mentioned before? Renerpho (talk) 20:04, 5 July 2024 (UTC)

  Adding Chirikov (1989), who specifies the lifetime as its "sojourn time" and gives a less involved explanation of the model than the scholarpedia artilce, I've reworded the part about its projected lifetime, and about the mathematical model. Hopefully this makes more sense now even without a graduate-level understanding of physics (which I cannot offer). The article now says: Halley's projected dynamical lifetime is estimated to be about 10 million years.^[49] The dynamics of its orbit can be approximately described by a two-dimensional symplectic map, known as the Kepler map, a solution to the restricted three-body problem for highly eccentric orbits.^[49][50] The various references to "these studies" in the rest of that paragraph are still confusing, and need to be untangled before this can be marked as "fixed". Renerpho (talk) 08:59, 8 July 2024 (UTC)

•  Pending Quote from the article: Another point of origin for the Halley-type comets was proposed in 2008, when a trans-Neptunian object with a retrograde orbit similar to Halley's was discovered, 2008 KV42, whose orbit takes it from just outside that of Uranus to twice the distance of Pluto. It may be a member of a new population of small Solar System bodies that serves as the source of Halley-type comets. The source for this is currently Gladman (2009). However, Petit et al. (2017)[37] says that "these objects may point to a new source that feeds large-i TNOs into the planetary system (Gladman et al. 2009). This may simultaneously be the source of the Halley-type comets (see Levison et al. 2006)", so it seems they credit the idea to [38]. Whether that's justified or not, Levison's work is currently not referenced by our article, and I think it should be.
  It's worth looking for dynamical studies that were published more recently, perhaps based on other objects. 2008 KV42 is no longer the only object of this kind (the Minor Planet Center lists 15 objects with similar orbits[39], most of them discovered in the last ten years). Renerpho (talk) 22:05, 5 July 2024 (UTC)
•  Pending Quote: Observations conducted around the time of Halley's appearance in 1986 suggested that the comet could additionally perturb the Eta Aquariids, although it might not be the parent of that shower. That's blatant nonsense. The comet wouldn't be able to perturb a meteor shower (what mechanism would be at play for such a perturbation? gravity??), and it is very much the parent body of that shower. Why did the author expect an increase in Eta Aquariid activity during 1983-1986, when the shower is associated with outbursts that occurred during the 1st millennium AD? Why do we give WP:UNDUE weight to a single sentence written by an author who, as far as I can tell, has never published anything about astronomy before or since, and whose credentials are a secondary school? Is that article even peer-reviewed? Why not instead cite the seminal paper on the issue, Egal (2020)? Renerpho (talk) 05:48, 6 July 2024 (UTC)
•  Pending Quote: Unusual for an object in the Solar System, Halley's orbit is retrograde; it orbits the Sun in the opposite direction to the planets, or, clockwise from above the Sun's north pole. Are they unusual in general (yes)? For Halley-type comets (no)? We need a citation here. Renerpho (talk) 06:52, 6 July 2024 (UTC)
•  Pending Quote: (Because it is retrograde, the true inclination is 162°.) Why is this put in brackets? We're not doing this anywhere else in the article, and I don't understand what motivates it here. The reference[40] neither includes the words "retrograde" nor "two inclination", instead leading to a random(?) computation of Halley's orbit before 760 AD. Why is that relevant here? Renerpho (talk) 06:03, 6 July 2024 (UTC)
•  Pending Quote: As of 2015, only 75 Halley-type comets have been observed, compared with 511 identified Jupiter-family comets. We should update that figure (the source is kept up to date, as of 2024). But more importantly, I don't think the figure we give here was correct in 2015, and it wasn't supported by the source:[41] It says that it's doing a naive classification, and that "no attempt has been made to exclude comets with HT-like inclinations or periods (See "unusual members" below.)". Okay, so, do we manually subtract the objects listed there? Has that been done in 2015? Why don't we use a more authoritative source, like JPL's "Comet Orbit Classes"?[42] Renerpho (talk) 06:14, 6 July 2024 (UTC)
•  Pending Quote: it has one of the highest velocities relative to the Earth of any object in the Solar System -- Source? Context? Maybe we could point to someone who talks about the velocity distribution of comets? Fig.4 in [43] comes to mind, although it doesn't mention Halley's Comet specifically. I am also looking for a reference that explains why 72 km/s is the upper limit (something better than [44]). If anyone can find a good one, that'd be nice. Renerpho (talk) 06:35, 6 July 2024 (UTC)
•  Pending Quote: Halley's orbital period has varied between 74 and 79 years since 240 BC. Brady (1982) disagrees.[45] For instance, the table on p.210 gives an anomalistic period of 79.26 years during the 530 AD apparition, and a keplerian period of 79.34 years in 1066 AD. In 1145 AD, both were larger than 79 years. I don't know which one we're supposed to use (the anomalistic period, I guess, although "orbital period" is more commonly understood to be keplerian), but our claim isn't true for either of them, so it doesn't really matter. Renerpho (talk) 06:47, 6 July 2024 (UTC)

Problems in Structure and composition section

I've made a first pass of the first two paragraphs of this section (I'll look at the remaining two paragraphs later). A number of issues could be fixed immediately, see the list of "fixed" issues, and the recent revisions to the article, but many could not: Renerpho (talk) 09:07, 6 July 2024 (UTC)

•  Pending Quote: Its mass is relatively low -- relative to what? Halley is one of the most massive comets known, owing to its size. Renerpho (talk) 07:20, 6 July 2024 (UTC)

  Even if we take this to mean "relative to its size" (thus referring to density), I still think it's wrong. We don't know the densities of many other comets. The only exception is 67P, whose nominal density is even lower than Halley's. Densities in that range (near 0.5 g/cm³) could be typical. Renerpho (talk) 04:24, 7 July 2024 (UTC)

•  Pending Quote: Gas molecules in the coma absorb solar light and then re-radiate it at different wavelengths, a phenomenon known as fluorescence -- There is no reference for this. I'd suggest to change the link to resonance fluorescence, and then select one of the papers from [46] as a citation. However, I'm not entirely sure if this isn't approaching WP:SYNTH territory. Note that neither of Comet, Comet tail or Coma (comet) mention the word "fluorescence", and doing so here could be undue. A search for articles that explicitly link the glow of comets to fluorescence brings up very few convincing results. Renerpho (talk) 07:46, 6 July 2024 (UTC)
•  Pending Quote: As a fraction of the gas molecules in the coma are ionized by the solar ultraviolet radiation -- Our reference [47] mentions neither ionization nor UV radiation. Renerpho (talk) 07:58, 6 July 2024 (UTC)
•  Pending Quote: pressure from the solar wind, a stream of charged particles emitted by the Sun, pulls the coma's ions out into a long tail, which may extend more than 100 million kilometres into space -- Our source (Biermann, 1958) says: "They may ultimately form the comet's tail, which in some cases extends 100 million miles". I don't see why we change that to "more than 100 million km", even though I guess it's not wrong... Are we afraid of imperial units? Renerpho (talk) 08:03, 6 July 2024 (UTC)
•  Pending Quote: Ground-based observations of coma brightness suggested that Halley's rotation period was about 7.4 days. Images taken by the various spacecraft, along with observations of the jets and shell, suggested a period of 52 hours. -- Here's what our source says about this (Keller et al., §2.2.5, p.216):[48] "Shortly after the encounters with Comet Halley, the rotation period of the nucleus was derived by comparing the various images during the three flybys. In a first-order approach, a stable rotation around the axis of maximum inertia (perpendicular to the long axis) was assumed (Wilhelm, 1987; Sagdeev et al., 1989). Fits were found for a period slightly above 50 h (2.2 d). Groundbased observations of the coma brightness variations yielded a period of about 7 d, but dynamical features (jets, shells) were in agreement with the 2.2-d periodicity. It is now widely assumed that the spin state of Comet Halley is excited, i.e., that the rotation is not in its energetic minimum and includes nutation (Sagdeev et al., 1989; Samarasinha and A’Hearn, 1991; Belton et al., 1991). There is no common understanding of the details (Keller and Jorda, 2002). Three flybys and a long series of groundbased observations were not sufficient to pin down the rotational parameters."
  I think we should sight the papers mentioned there, and update our article accordingly. Right now, we neither discuss possible reasons for the discrepancy between groundbased and in-situ observations, nor the rest of what's known about Halley's rotation (including the ongoing debate about the details). And by the way, where did we get the figures of 7.4 days and 52 hours? Clearly not from the source we're citing... Renerpho (talk) 08:17, 6 July 2024 (UTC)
•  Pending Quote: Changes in the flow of the solar wind can cause disconnection events, in which the tail completely breaks off from the nucleus. -- Writing about two of the disconnection events (DE) that were observed during Halley's 1986 apparition, the authors of our source (Brosius et al., p.267-275) attribute them to a reversal in the polarity of the interplanetary magnetic field. Since Brosius only looked at two specific DE, that's not really a satisfactory citation for what we're saying. I think the article Plasma structures in comets P /Halley and Giacobini-Zinner by Brandt&Niedner, p.281-286 in the same volume, is more interesting. They look at all 16 DE observed in 1985/86, and more broadly address the history of the study of DE, from the early 1900s to the rediscovery of the phenomenon by the authors in 1978 and the conclusions from observing comet Halley. Renerpho (talk) 08:46, 6 July 2024 (UTC)

The last two paragraphs of the section (most issues with this could be fixed immediately): Renerpho (talk) 04:14, 7 July 2024 (UTC)

•  Pending Quote: Halley is the most active of all the periodic comets, with others, such as Comet Encke and Comet Holmes, being one or two orders of magnitude less active. -- Our source[49] says that Halley is "one of the most active short-period comets" (highlight by me; there's no further reference for this claim which is made in passing). It doesn't mention the comets Encke and Holmes, and it doesn't say how much their activity differs from Halley's. It says that "the activity of Comet Borrelly was more than one order of magnitude lower than that of Comet Halley" when 19P/Borrelly was visited by a spacecraft, and that "Comet Halley is the most productive short-period comet, but yet only a minor fraction of its surface is active. Typical Jupiter-family comets display activity levels one or two magnitudes less than this, e.g., Comet Borrelly." Is that the same thing we're saying? If so, why the "one of" qualifier in the other quote, and why the different terms (activity vs. productivity). I think we're not faithful to the source. Renerpho (talk) 09:03, 6 July 2024 (UTC)
•  Pending Quote: Halley's albedo, for instance, is about 4%, meaning that it reflects only 4% of the sunlight hitting it – about what one would expect for coal. Thus, despite appearing brilliant white to observers on Earth, Halley's Comet is in fact pitch black. -- That the comet appears brilliantly white from Earth is due to light scattering in the coma, not light reflected from the surface of the nucleus, so the second sentence (which doesn't have a citation) doesn't follow from the first (and is, in fact, wrong). Renerpho (talk) 03:55, 7 July 2024 (UTC)
•  Pending Quote: More recent work suggests that Halley will evaporate, or split in two, within the next few tens of thousands of years, or will be ejected from the Solar System within a few hundred thousand years. -- The issue is the word "evaporate". I am conflicted on this one. I have changed most instances throughout the article from "evaporate" to "sublime", but this here seems to be a different sense of the word "evaporate", which could be acceptable. Opinions? Renerpho (talk) 04:13, 7 July 2024 (UTC)

Problems in History section

General comments

•  Pending In his book The History of Halley's Comet (currently ref.31), David Hughes writes that "It's[sic] brightness near perihelion is such that, in any random selection of historic comets, P/Halley appears at the frequency of about 1 in 8." Ignoring the typo, I find that statement interesting, and suggest that we include it. We currently provide no context for the various collections of historical observations we use, and this would work nicely. Renerpho (talk) 06:32, 7 July 2024 (UTC)
•  Pending Ref.59 (a 2010 BBC News story) is based on an article in Journal of Cosmology,[50] which is not peer-reviewed, and is generally regarded as WP:FRINGE. BBC News may generally be reliable, but it's not useful for science news. Renerpho (talk)

  I've moved this back from the "fixed" section. This has made it into a lot of sources that we would generally regard as reliable. Phys.org talked about it, taking it at face value. NewScientist treats it as fact as well. Neither of them question the obvious problems with a source that isn't peer-reviewed, or with the fact that the lead author is a philosopher (not a historian or astronomer). Just ignoring this may not be feasible, and I think we have to mention it in some form. Taking it as truth isn't an option either. Renerpho (talk) 00:56, 5 July 2024 (UTC)

  The discussion about the "Computation of orbit" section, particularly about the various studies by Cowell&Crommelin (1907-1910) and Pontécoulant (1829-1835), may inform how to deal with this. Renerpho (talk) 09:23, 6 July 2024 (UTC)

I am not going to systematically check the sections about 1835 and earlier, until we have rewritten the Halley's Comet#Computation of orbit history, currently being discussed above (otherwise I risk wasting my time). For the years 1910 and later, here's what I have so far: Renerpho (talk) 15:08, 7 July 2024 (UTC)

Before 1066

(Currently none)

1910

•  Pending Quote: The comet added to the unrest in China on the eve of the Xinhai Revolution that would end the last dynasty in 1911 -- Source? Xinhai Revolution says nothing about the comet, despite its vast coverage. Hutson's quote doesn't establish either that the appearance of the comet had any significance, just that some people in some places acted irrationally, but there would be constant revolution everywhere if that was enough! Renerpho (talk) 12:33, 7 July 2024 (UTC)
•  Pending Quote: The 1910 visitation is also recorded as being the travelling companion of Hedley Churchward, the first known English Muslim to make the Haj pilgrimage to Mecca. However, his explanation of its scientific predictability did not meet with favour in the Holy City. -- Our reference for this (Rosenthal, 1931) needs a page number. Right now, I cannot verify if anything like this is supported by the source. I'm not even sure what we're trying to say here, so I guess this will have to be expanded by at least another sentence or two. The only mention of the comet in our article about Hedley Churchward is this: Having arrived in Jeddah, Hedley encountered no problem with the officials and set off the following evening with two donkeys and a pilgrim guide with Halley's Comet a brilliant spectacle in the heavens. It doesn't come with a reference; in fact, the entire story about Churchward's haj in that article is completely unreferenced. Renerpho (talk) 12:44, 7 July 2024 (UTC)

Rosenthal (1931) is here in a poor but mostly legible scan. AstroLynx (talk) 13:42, 7 July 2024 (UTC)

Using the archive's search function, which works reasonably well despite the poor scan, here are two quotes from Rosenthal (1931) that could be relevant:

Page 81: Learned Mahomedans told me it was a very fortunate omen seeing that it occurred during my Pilgrimage. Every Arab I found studying the spectacle showed impressive reverence for the work of the Almighty. Throughout the journey, I beheld that wonderful belt of flame over the Northern sky and I think Halley’s Comet added a good deal to my prestige.

Page 144: Our talk drifted, and presently we looked at the comet. "These people," said the Matof [pilgrim guide, ed.] pointing at his companions, "think yon are a lucky man to have come with such a stat."

I find nothing about the reception of him trying to explain it scientifically, but maybe it's hidden somewhere (reading the whole book would take too long). Renerpho (talk) 06:23, 8 July 2024 (UTC)

I would have liked to ask the user who added this, but unfortunately it is from an IP who only made a single edit (08:53, 12 June 2016). Renerpho (talk) 07:39, 8 July 2024 (UTC)

•  Pending Quote: Twain died on 21 April 1910, the day following the comet's subsequent perihelion.^[126] -- Our current ref.126 doesn't mention the comet. If the source is meant to be for the day of death the (which I don't think needs a source, but okay) then it should be put after the day of death. We'd still need a source that connects the time of the perihelion passage with Twain's passing, to avoid WP:SYNTH issues. Renerpho (talk) 13:24, 7 July 2024 (UTC)

1986

•  Pending Quote: Scheduled for March 1986, STS-61-E was a Columbia mission carrying the ASTRO-1 platform to study the comet -- I would like to add a wiki-link for ASTRO-1, but I'm not sure what to use. The related article STS-35 does something strange, writing "ASTRO-1, a Spacelab observatory consisting of four telescopes", where the wiki-link for ASTRO-1 is a manual redirect to Astronomy. I find that a rather odd thing to do. Renerpho (talk) 07:53, 7 July 2024 (UTC)

  ASTRO-1 consisted of four separate telescopes, and we have articles for two of them: Hopkins Ultraviolet Telescope and Wisconsin Ultraviolet Photo-Polarimeter Experiment. The latter doesn't mention that it was part of the ASTRO-1 mission, while the former has a manual redirect from Astro-1 mission (sic) to STS-35. Neither mentions Halley's Comet, or that the mission had been delayed after the Challenger disaster. Renerpho (talk) 08:15, 7 July 2024 (UTC)

After 1986

(Currently none)

2061

•  Pending Quote: when it will be better positioned for observation than during the 1985–1986 apparition, as it will be on the same side of the Sun as Earth. -- The reference we use, Yeomans (1986), only tentatively supports this. The text says nothing about either the 1985–1986 or the 2061 apparitions. The only thing of relevance is figure 3, page 70. I'd like to have a source that actually interprets it for us, and Yeomans doesn't do this. In fact, I don't think that figure means quite the same thing we're saying. Renerpho (talk) 14:59, 7 July 2024 (UTC)

2134

(Currently none)

Problems in Apparitions section

•  Pending In the introduction to the apparitions table, it says: Perihelion dates of 1531 and earlier are in the Julian calendar, while perihelion dates 1607 and after are in the Gregorian calendar, with [51] as the source. I was uncertain if that was how we should do it, considering that most of Europe only switched to the Gregorian calendar around 1700. In particular, Halley himself would have used Julian dates exclusively.[52] So I checked how our source(s) do it, and there's a problem: Our table gives 27 October as the date of the 1607 perihelion, while the source gives it as "1607 October 26.80", but clearly says that this is the Julian date. One of the two is wrong. I'd usually say that we're wrong and the table is right. Small discrepancies (of order <1 day) aside, the problem is that JPL's Small Body Database gives the date of the 1607 perihelion as JD 2308304.0406, 1607-Oct-27.5406 (see select orbit, 1607-Oct-24), and those are only the same date if the latter is meant to be Gregorian.[53] JPL admits on their page that the epoch for the 1607 orbit may be ambiguous, and that they do not know what the correct epoch in their source is meant to be, so whether they can be trusted as a source for the date is unclear. Still, we have two reliable sources that contradict each other, and our article contradicts the source we're citing. Renerpho (talk) 23:04, 30 June 2024 (UTC)

  By the way, the source we're citing also gives a Julian day for the 1607 perihelion (2308303.79922), which is inconsistent. The Minor Planet Center, which is the 2nd source we're citing for the date, take theirs from JPL, but as I said, JPL themselves don't seem to trust it... Renerpho (talk) 23:07, 30 June 2024 (UTC)

  A way to resolve this may be through the work of Kiang (1961), [54], page 27ff: Brady (1982)[55] cites Kiang, and compares their results. On p.214, Brady gives the differences between his perihelion dates and Kiang's, noting that Kiang's date for the 1607 perihelion differed from his by just -0.26 days. Kiang's article isn't available online, but if someone can access a physical copy,[56] and find out what dates Kiang gives (ideally with the Julian day, if available) for the apparitions between 1531 and 1758, the question could be settled. Renerpho (talk) 17:48, 5 July 2024 (UTC)

  Another way is looking at the other values in Brady's table, and checking them for consistency: He gives the anomalistic period, the time between consecutive perihelion passages, to 0.01 year accuracy. Using the differences between his Julian dates to calculate the anomalistic period manually does agree with those numbers (1531: 75.21 vs. 75.2120; 1607: 76.14 vs. 76.1445; 1682: 74.89 vs. 74.8872), while doing the same with the calendar dates does not. This suggests that Brady's Julian dates were probably correct, but that he has mislabeled his calendar date for the 1607 apparition. I say "probably" because, if Brady used the Julian dates to compute the anomalistic period (which would be applying the definition of P_anom) then any error in one of them would produce a self-consistent error in the other. Renerpho (talk) 18:13, 5 July 2024 (UTC)

  I'd usually give Brady the benefit of the doubt, but since it is certain that there is an error somewhere in his table, I'm not going to in this case. Renerpho (talk) 18:21, 5 July 2024 (UTC)

  @AstroLynx: Can you find Kiang's article (in Memoirs of the British Astronomical Association: Reports of the Observing Sections, volume 39, issue 3, 1961)? No library within 200 miles of my location has a copy of it. Renerpho (talk) 16:48, 7 July 2024 (UTC)

Our library probably has it but it will take one or two days before I have it on my desk. It appears to be a supplement or addendum of J.G. Porter's Catalogue of Cometary Orbits (Equinox 1950.0). In the mean time, perhaps this paper is also useful. AstroLynx (talk) 19:35, 7 July 2024 (UTC)

@AstroLynx: Great, thank you! The table on p.19f is interesting, but Hasegawa's periods don't agree with any of Brady's so I suspect they are keplerian rather than anomalistic. Hasegawa doesn't provide Julian days for the perihelion passage, but he does say his dates are Julian prior to 1583, and Gregorian after that. Hasegawa's 1607 perihelion date is Oct 27.22, in close agreement with Brady's, indicating that Brady had in fact meant to say that the 1607 date was Gregorian. This would mean that the dates we give in our table, while not agreeing with our source, are factually correct as they are. If you've already ordered Kiang's article then we may as well check his work, just to be sure (Brady's reference to it makes it the best possible test).
Btw, what's "J. Holetschek, A.N., 143, 113." (Hasegawa's source for the 66 AD apparition, p.44)? Renerpho (talk) 21:00, 7 July 2024 (UTC)

Hasegawa refers to this paper in the Astronomische Nachrichten. AstroLynx (talk) 21:08, 7 July 2024 (UTC)

A fun case where, by misquoting it, we cancel out an error in the source. Renerpho (talk) 21:03, 7 July 2024 (UTC)

•  Pending Chang wrote in 1979 about the evolution of the comet's brightness since ancient times: "It should be noted that, of the maximum brightness at each return estimated from the observational records, the magnitude was as bright as -5^m - -7^m at ancient times. Subsequently, the brightness decreased to -1^m - +1^m. Such changes in the brightness are certainly not due to its varying distances from the Earth or the Sun, but are caused by the weakening of its intrinsic power. [...] It is not difficult to understand that its intensity will weaken after a number of returns." I believe we have nothing on that question in the article. Renerpho (talk) 15:21, 5 July 2024 (UTC)

  I would like to add a column to the table of apparitions, giving the brightness, as reconstructed by Zhang Yuzhe in 1979. Starting with the apparition of -12 BC (return cycle -26), Zhang computes, based on historical records and his model of the comet's orbital evolution: -26: -5^m; -25: -7^m; -24: -4^m; -23: -4^m; -22: -3^m; -21: -3^m; -20: -3^m; -19: -3^m; -18: -4^m; -17: -2^m; -16: -2^m; -15: -3^m; -14: -2^m; -13: -1^m; -12: -4^m; -11: -2^m; -10: -1^m; -9: -1^m; -8: -1^m; -7: 0^m; -6: -1^m; -5: 0^m; -4: 0^m; -3: -1^m; -2: 0^m; -1: 0^m; 0: +2^m (predicted! - the actually observed brightness in 1986 was +2.1^m). Renerpho (talk) 15:49, 5 July 2024 (UTC) Renerpho (talk) 15:49, 5 July 2024 (UTC)

  It could make sense to also mention this elsewhere in the article, like in Structure and composition. Renerpho (talk) 20:17, 5 July 2024 (UTC)

  One of our sources, Yeomans, Great Comets of History, gives maximum brightnesses for some historic comets, including many apparitions of Halley. However, I don't know how his numbers should be interpreted. For instance, he lists the maximum brightness of Comet Skjellerup–Maristany in 1927 as +1 mag, even though that comet was visible in daylight 4° from the Sun (you'd struggle to see the Moon in that position). Comet Ikeya–Seki in 1965 is listed as +2 mag, whereas other sources give it as -12 mag (one of the brightest comets of all time). Renerpho (talk) 12:07, 7 July 2024 (UTC)

•  Pending Our table is using Kinoshita and Yeomans as references. Yeomans is the general source for the Earth approach, and Kinoshita is used for some of the perihelion dates (also in the lede). Right now, Yeomans is our source for the Earth approach in 2061; it says nothing at all about that apparition. Kinoshita gives a distance (0.5543 au), but it is different from ours (0.477 au). Renerpho (talk) 15:55, 7 July 2024 (UTC)
•  Pending What's the source for the "visible duration" in the Halley's Comet#Apparitions table? There's nothing about this in the source we're citing (Brady, 1982), and it contradicts what we say elsewhere. Compare, for example, note b about Giotto's observation of the 1301 apparition, which was visible at least from 16 September to 1 November, possibly into January of the following year. Renerpho (talk) 17:13, 5 July 2024 (UTC)

  One of the sources we already use, Yeomans, Great Comets of History, gives a number of visibility intervals in his table. He doesn't list all apparitions, but enough that it may be be useful: 1910: 10 April–29 June; 1682: 15 August–25 September; 1531: 5 August–8 September; 1456: 26 May–9 July; 1378: 26 September–11 October (hindered by cloudy weather in October); 1301: 1 September–1 November; 1222: 2 September–8 October (observed in daylight from Japan on 9 September); 1145: 15 April–19 June; 1066: 2 April–7 June; 989: 10 August–11 September; 837: 21 March–29 April; 760: 16 May–5 July; 684: 6 September–9 October; 607: March–April; 451: 9 June–16 August; 374: 3 March–4 April; 295: May–June; 218: May–June; -11: 25 August–21 October. -- I have highlighted one fact about the 1222 apparition that we do not yet mention in the history section.
  We need different sources for the other apparitions. The most recent apparition of 1986, which we currently say was only visible for a single day(!?), was first seen with the naked eye on 8 November 1985; I don't know what the end day should be. The history section lacks information about ground-based observations following the first sighting, despite its extensive coverage of space missions. Renerpho (talk) 12:02, 7 July 2024 (UTC)

  Yeomans (1986), table 1, pages 71-77[57] is exactly what we need. It works for all apparitions from 240 BC to 1910. Any objections against replacing the dates in our table with his? We still need an end date for the 1986 apparition... Yeomans (1986) also works as a source for a lot of historical observations, and for what we may put in the "Description" column. Renerpho (talk) 16:06, 7 July 2024 (UTC)

  I've tracked down where that "visible duration" information comes from. In an edit on 15 November 2016,[58] the contents of a table from Historical comet observations in China were copy-pasted into the Halley's Comet article. While the "visible duration" makes sense in the context of the other article (showing when the comet is documented in Chinese records), it makes no sense in ours, where a different meaning is implied. I think this is called "Chinese whispers"...

  @Serendipodous: I see no reason to keep the dates as they are. What do you think about the replacement I've suggested (Yeomans, 1986, table 1, p.71-77)? As for the last naked-eye sighting in 1986, the date should be given in [59], p.189-190. The date of 8 November 1985 for the first sighting is given on p.189; the total duration for which it remained visible, about 6 1/2 months, is on p.203. The section with the date of the last sighting, which should be some time around May 1986, is apparently not available online. Do you have more luck? Renerpho (talk) 13:37, 8 July 2024 (UTC)

  Relevant to this is this edit in the deletion discussion for Historical comet observations in China, from the same date in 2016. @Primefac: Do you remember this? You argued back then that I have moved the table about Halley's Comet to that article, as) it should be there, and b) a vast majority of the information wasn't specifically from China. I don't disagree that the info should be kept somewhere, but maybe in a different form? Since we're about to remove it, do you have any suggestions what to do with it? Renerpho (talk) 13:46, 8 July 2024 (UTC)

•  Pending Quote, referring to the 1378 apparition: This is the last appearance of the comet for which eastern records are better than Western ones. -- Is that an editorial statement? The scientific consensus? An obvious fact? There is no citation, and our history section doesn't compare the quality of eastern and western records, certainly not for the 1378 apparition. By the way, should we capitalize both, or neither? Renerpho (talk) 07:48, 8 July 2024 (UTC)
•  Pending Quote: for every apparition of Halley's Comet from 240 BC, the earliest documented widespread sighting -- Do we have documentary evidence that the 240 BC apparition was a "widespread sighting"? Kronk, p.6[60] says that the 240 BC apparition is known from a single source with "scant details". The same is true for some of the other apparitions from antiquity. Renerpho (talk) 12:34, 8 July 2024 (UTC)

References