Talk:Halley's Comet

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164BC Discrepancy[edit]

The 2nd list item under Apparitions identifies the date as 12 November 164 BCE, while the caption for the image of the tablet in the first subsection (Prior to 1066) states "Observation of Halley's Comet, recorded in cuneiform on a clay tablet between 22 and 28 September 164 BCE, Babylon, Iraq. British Museum."

Which was it; September or November? — Preceding unsigned comment added by Wikierroneous (talkcontribs) 14:31, 24 July 2013 (UTC)

November 12 was the date of perihelion. It was visible before that date. Saros136 (talk) 08:16, 16 May 2014 (UTC)
Babylonian tablet recording Halley's comet.jpg
Cuneiform tablet recording observation of Halley's Comet.JPG

A second contradiction:

Left pic: A Babylonian tablet recording Halley's comet during an appearance in 164 BC. At the British Museum in London „(you can see 41462 in the text)

Right pic: Observation of Haley's Comet, recorded in Cuneiform on a clay tablet between 22-28 September 164 BCE, Babylon, Iraq. British Museum, London. BM 41462

--Palitzsch250 (talk) 19:04, 4 April 2014 (UTC)

Era Names[edit]

I remember reading this page some years ago, and have noticed that the era names were changed from BC/AD to BCE/CE over that time. Looking over the revision history, it seems that Materialscientist switched them over on Oct. 23, 2011, and has been reverting attempts to change them back. However, the original change appears to me to be in contradiction to WP:BCE, which states "Do not change the established era style in an article . . . A personal or categorical preference for one era style over the other is not justification for making a change;" and "Seek consensus on the talk page before making the change." Since this has been a cause of repeated edit warring over the past two years, pending discussion here, I'd like to change them back to the original style which was present for the previous nine years. Korossyl (talk) 17:01, 3 December 2013 (UTC)

Agreed. Please do. Lachrie (talk) 05:10, 8 December 2013 (UTC)

Good catch! However, for precision, it looks like the initial wholesale change was made by User:Eastaer. Materialscientist then caught some stragglers, leaving an edit summary that said something about "consistency of eras". Materialscientist does not seem to have edited the article for almost two months prior to that, so it's possible (s)he didn't notice that the longstanding usage here was AD/BC. --Trovatore (talk) 04:13, 10 December 2013 (UTC)
Ah, right back at you. I missed that, thanks! And apologies, then, to Materialscientist for the misidentification. Korossyl (talk) 12:52, 10 December 2013 (UTC)

Non-gravitational effects[edit]

The sentence I replaced , These orbital changes can cause deviations in its perihelion of four days, seems supported by the source if we take its statement about 1P/Halley without context. As if to say four days is the maximum, and presumably the average is less. A book by the same author, Comets, makes it clear that four days is about the average difference and that it comes late. I'm going to put more about the NG forces too. Saros136 (talk) 07:31, 18 May 2014 (UTC)

calculation of the comets return[edit]

I removed the statement did not pass through its perihelion until 13 March 1759, the attraction of Jupiter and Saturn having caused a retardation of 618 days.I haven't seen the source for the sentence I removed, but the same thing is in Comets, by Yeomans, so I'll judge it using that book. Referring to the calculations by Alexis-Claude Clairaut before the recovery in 1758. Yeomans wrote ...Clairut established that the interval between the 1682 and 1759 perihelion passage would be 618 days longer than the corresponding interval between 1607 and 1682; 518 days due to Jupiter's influence and the remaining 100 days due to Saturn's. His calculated date was nearly 33 days too late, and the 618 days refers to that calculation. Jupiter and Saturn do not account for all the diifferences either; they didn't know about Neptune and ignored smaller planets. But those aren't the biggest problems. The 1607-1682 interval was not a demonstration of the unperturbed orbit, so the longer interval is not a sign that Jupiter and Saturn had that long of a retarding effect in the 1682-1759 one. Better ways to compare the effect of perturbations are to use the period given (or deduced from) orbital elements at one pass, or for better and more refined comparisons use software to make calculations for both the real and unperturbed orbits. For the first method, the JPL Horizons period from 1682 elements, 28287.21 days as opposed to the actual gap of 27,937.76 days between the two perihelion dates which suggests the perturbations shortened the gap by 350 days. There are some factors ignored here, so for the more refined method I've used Solex. (To ignore perturbation of the planets on the minor bodies, the user needs to right-click on the names of the chosen planets.) the predicted 1759 date was March 16.66, and for the unperturbed comet it was June, 14.0, later by 89.3 days. Using only the perturbations of Jupiter and Saturn the date is March 23.57, earlier than the unperturbed one by 82 days. The planets made the comet reach perihelion earlier. Saros136 (talk) 15:27, 17 October 2014 (UTC)

This is original research. Can't you just put the source back with the line rephrased? Serendipodous 17:58, 17 October 2014 (UTC)
I do get carried away with this stuff. I would not use my investigations as a source-OR-but if I discover a truth, it is something that probably can be sourced. That each orbit is perturbed, and that Jupiter and Saturn have the greatest but not the only effect, can be. That other effects were neglected for practical reasons or were unknown can be. In fact this can all be found in the book I used. It can be demonstrated with simple arithmetic that the 1682-1759 gap is shorter than the average one observed, and this means the length of the 1682-1759 interval is not a sign of a retarding effect by the giant planets.
I would like to make a contribution, not a rephrasing, to this article on Clairaut's work. Yeomans's book is a history of observations and research on comets and will be an excellent source. The problem is space of course is space. There should be even more about the calculations leading up to the 1910 apparition, which were more important scientifically. I'm thinking we should have another article on the history of the calculations here. Saros136 (talk) 05:29, 18 October 2014 (UTC)
Still, with all due deference to your scientific knowledge, until you do find a source, I'm keeping the sourced information in. This would appear to be a WP:VNT situation. Serendipodous 08:07, 18 October 2014 (UTC)
It is not a matter of sources or VNT. Whoever wrote the item in question would have written exactly the same thing with the book I mentioned by Yeomans. He may have drawn from the one that is the source for the article, although Yeomans wrote about the subject a long still earlier. But there is more to the story. The 618 day effect is presented only as a prediction of Clariut, with uncertainty. His calculations were hurried, so he could announce the prediction before the recovery of Comet Halley. Claiuit said give or take a month, and that was about what the error proved to be. He naturally neglected the effects of the smaller planets. That is why he wrote as if difference between the 1607-1682 and 1682-1759 gaps was due the effects of Saturn and Jupiter.By the way, ithe second of those intervals was 585 days longer. He did in fact succeed in presenting the results before recovery. Later he refined his prediction, corrected errors, and got a more accurate date. Yeomans's book also has a more modern analysis of the source of his errors. Saros136 (talk) 06:58, 20 October 2014 (UTC)
OK, then cite Yoemans' book and rewrite the line. Serendipodous 07:02, 20 October 2014 (UTC)
This is what I was planning: The comet arrived at perihelion on March 13, 1759, which was 76.49 years after the last pass, which is shorter than the average interval since it has been observed, but 585 days longer than the one from 1607-1759. The key prediction was made by Alexis-Claude Clairaut, who said the gap time between the 1682 perihelion and the upcoming 1759 one would be 618 days longer than the preceeding one, give or take a month. Clairaut hurried the calculations so he could present the results before the recovery, but after the comet left he refined his calculated date and got a more accurate one. There was controversy over whether his original prediction should be considered accurate or not, with his supporters and detractors using different standards. This is an additional source: Saros136 (talk) 07:11, 20 October 2014 (UTC)
The key element of the phrase you removed was how the actual date of arrival differed from Halley's prediction. That's what the line is about. If there are other considerations, then they should be included, but they are secondary. Serendipodous 07:24, 20 October 2014 (UTC)
The 618 day figure and the April 13 date both come from Clairaut. Saros136 (talk) 17:28, 20 October 2014 (UTC)

[outdent]Yes, but they still need to be contrasted with Halley's figures. Serendipodous 22:57, 20 October 2014 (UTC)

Halley didn't give figures. His methods were to not good enough to be very precise. He initially predicted 1758-1759, sometimes wrote it would come in 1758, but in 1717 (a later work) , in a paper published posthumously, predicted late 1758 or early 1759. Saros136 (talk) 05:35, 21 October 2014 (UTC)
Then that needs to be in there too. Serendipodous 09:54, 21 October 2014 (UTC)

Magnitude during 1986 return.[edit]

The attribution for the statement that 1P/Halley only reached magnitude +2·1 during its 1986 passage notes that quantity as being its observed magnitude on the day of its predicted maximum brightness. Between 19 and 25 April the comet unexpectedly brightened by one magnitude to reach its true maximum brightness, making it a naked eye object in the evening twilight. [1] User: DavidFRAS (password forgotten). — Preceding unsigned comment added by (talk) 14:57, 5 January 2015 (UTC)

Protection of Halley's Comet?[edit]

I'm not sure where to put this, although I'm sure there's a specific method somewhere which I am violating, but in the last few months there's been a bit of IP vandalism; earlier IPs had been making constructive edits, but recently they've vandalized the article 7 times in the last few months alone. Perhaps a temporary protection (~1 month) on the article? Most other articles on significant celestial bodies are protected, including all of the planets and the Sun. exoplanetaryscience (talk) 18:40, 20 March 2015 (UTC)