Talk:Halley's Comet/Halley's Comet archive 2
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[edit] Perhelion date
Next Perhelion date off. I've only seen other sources say that Halley is due back in early 2062 not July 2061. My own calculations say Febuary 18th 2062.—The preceding unsigned comment was added by 65.110.226.202 (talk • contribs).
- What calculations did you use (how did you calculate it?)?--Gephart 15:00, 5 September 2006 (UTC)
Correction to my note above, the date calculated is March 17th or 18th (depending on the method you use for adding up leap years, I personaly believe the 17th is more accurate). These are the calculations:
a = 17.9564 AU AU = 1.495979*10^11 m e = 0.967298 last perihelion Feb 9th 1986 mu = 6.67259*10^-11 * Msun Msun = 1.988435*10^30 kg
T= 2*pi*(a^3/mu)^0.5
T = 2.40156*10^9 seconds
from here you can show that 2.4...E9 is 19.0252 multiples of 4 years, (365*3+366 days per 4 years) and it is .0252 * 4 years into the next set of 4 years (as long as the decimal is less than 0.5 for this particular calculation there will not be an additional leap year). This method finds there to be 36.81 days after febuary 9th 1962 to be the day of perihelion.
You can also use 365.2422 days per year and find the date to be 37 days after febuary 9th 1962 (slight error oscillates from + 0.5 to - 0.5 days depending on the x/4 remainder for this method, sometimes this 0.5 is enough to change the date.)
You can also use MSD (probably the better method of all 3 but I had already finished the first method, which find the same answer it just takes a bit more work) and Julian Date.
- Those calculations are too simplistic - they do not take into account the perturbations of the planets, which have a significant effect on the motion of this comet, given its long orbit. I put the original perihelion dates into the article, and they are based in part on calculations I did (using rigorous methods) and in part on researching the on-line scientific papers I could find about the motion of this comet (and I don't remember any of those scientific papers giving a perihelion date in March 2062 - any of them that gave a date in 2061 agreed on the date 28 July). I'm going to re-instate the correct date for the perihelion date in 2061. BTW did you run your calculations backwards? Do your results agree with the ancient sightings of the comet? I doubt that they could, as the motion of this comet is far from simple. Chrisobyrne 11:24, 7 September 2006 (UTC)
- Revert completed. If you are interested in the actual orbit elements and how they evolve over time, I can direct you to a web page I wrote about this -- Chrisobyrne 11:37, 7 September 2006 (UTC)
I won't change it, but I would like to say that my Aerospace Engineering Professor that teaches astrodynamics at Iowa State University is conviced that it is March 2062.
- Okay, here is what we need: Bring a citation of the orbital elements with a fixed epoch, like the one we have now. Then either cite the stated next estimated perihelion date in that source, or use the very simple logic of addition to come to a result. Because of WP:NOR we can not have numbers in here that are not referenced, but "just calculated" somehow. Awolf002 19:46, 7 September 2006 (UTC)
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- How's about this for a source - the JPL SSD Horizons web-based ephemeris generator. Asking it to generate heliocentric osculating orbital elements for 2061 Jul 28 generates a perihelion date of 2061 Jul 28.72. I could cite other sources, but this one has the advantage of working well for more than just Comet Halley. I've inserted a reference into the table. Chrisobyrne 10:38, 8 September 2006 (UTC)
[edit] Dates of perihelion
I have a confession to make. The table of the dates of perihelion came primarily from my own web site[1], and therefore arguably constitutes original research, in violation of Wikipedia policy. Therefore my table probably cannot be used on Wikipedia. I've removed it - it should not be re-instated. Chrisobyrne 14:55, 14 November 2006 (UTC)
- I've added sourced perihelion dates, from the Catalogue of Cometary Orbits 1996 via this website. Richard B 21:34, 14 November 2006 (UTC)
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- Unfortunately, I have (at least three) sources that contradict yours - for example, this one. The perihelion dates, especially in the distant past, cannot be relied upon - the comets motion is simply not known to that degree of accuracy, and the ancient observations are not accurate enough to pin down a perihelion date with anything like the degree of accuracy that you present. So I'm afraid your table is misleading. But, as we've already learned, Wikipedia has no problem whatsoever with misleading information in its articles. Chrisobyrne 21:57, 14 November 2006 (UTC)
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- You're using your own article (which you removed) to back up your claim here? I note that the ones I've added, from the "Catalogue of Comerary Orbits 1996", are not too far away from the ones in this peer-reviewed journal. Also, remember that the Catalogue of Cometary Orbits is published by the Minor Planet Center which is a branch of the IAU - and can therefore be assumed to be the most accurate dates that we have available. They take into account perturbations from all planets. Note also that this site says "Brian Marsden's Catalogue of Cometary Orbits has been the standard source for comet orbits since 1972". I'd say, therefore, that this data is likely to be the most reliable currently available. Richard B 22:28, 14 November 2006 (UTC)
- Actually, I'm able to use (if memory serves me correct) four articles from peer-reviewed journals to back up my claim, plus someone else's website. And, after what happened the last time I tried to gather sources for this page on the comet, I'm not going to waste my time listing those articles. Hey, I've only been studying the motion of this comet on and off for twenty years or so - what the hell would I know? Thank God we have Wikipedia to put me (and the scientific community) right. Chrisobyrne 23:10, 14 November 2006 (UTC)
- You're using your own article (which you removed) to back up your claim here? I note that the ones I've added, from the "Catalogue of Comerary Orbits 1996", are not too far away from the ones in this peer-reviewed journal. Also, remember that the Catalogue of Cometary Orbits is published by the Minor Planet Center which is a branch of the IAU - and can therefore be assumed to be the most accurate dates that we have available. They take into account perturbations from all planets. Note also that this site says "Brian Marsden's Catalogue of Cometary Orbits has been the standard source for comet orbits since 1972". I'd say, therefore, that this data is likely to be the most reliable currently available. Richard B 22:28, 14 November 2006 (UTC)
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- I would also add, that it is wikipedia policy that "The threshold for inclusion in Wikipedia is verifiability, not truth. "Verifiable" in this context means that any reader should be able to check that material added to Wikipedia has already been published by a reliable source." I'm sorry if you don't like that, but that is wikipedia policy. Richard B 23:37, 14 November 2006 (UTC)
- Richard - thank you for being a fantastic sounding board for me - I've learned a lot through our back-and-forth, and it has helped ease a couple of traumatic wikipedia days for me. There is a lot about the Wikipedia policy that I do not like, but verifiability is actually a policy I most certainly do like. However, I'm rapidly reaching the conclusion that Wikipedia articles should never be edited by experts, and I'm an expert. I'm going to develop that idea over the coming days - if it pans out, I might write an "experts" page about this comet somewhere - we'll see - and I hope to write something about why I believe Wikipedia articles should not be edited by experts. Again, thank you, and apologies for any distress caused by my earlier "attitude". Chrisobyrne 01:00, 15 November 2006 (UTC)
- I would also add, that it is wikipedia policy that "The threshold for inclusion in Wikipedia is verifiability, not truth. "Verifiable" in this context means that any reader should be able to check that material added to Wikipedia has already been published by a reliable source." I'm sorry if you don't like that, but that is wikipedia policy. Richard B 23:37, 14 November 2006 (UTC)
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[edit] Designation
The "Designation" table mentions the designation for the comet at its previous returns. For instance, the 240BC return is listed as "1P/-239 K1". I have a funny feeling that the designations have not actually been applied retrospectively and, even if they had, that the uncertainties in the comets motion mean that another calculation could end up designating it "1P/-239 J1" or something. Also, I cannot find the string "1P/-239 K1" anywhere on Google, so it musn't be true :). Does anyone have a reliable citation for the information in that table? If not, then I think it should be removed. Chrisobyrne 16:27, 14 November 2006 (UTC)
- Removed the table - the contributor of that table has now been given more time to come up with citations than I was given over the name issue. Given that there is an error of maybe a month or two in our knowledge of the comets first apparitions, assigning a designation isn't reliable. Chrisobyrne 20:47, 14 November 2006 (UTC)
Do we need this list? It says nothing interesting about the comet. George J. Bendo 10:32, 15 November 2006 (UTC)
[edit] Explanation needed
It would be useful to have an explanation of the details given at each perihelion (e.g. (1P/1982 U1, 1986 III, 1982i). Is there a reference for this? Duncan.france 23:22, 15 January 2006 (UTC)
- See Comet#Comet nomenclature - they are all different names for the same apparition of Halley's Comet. In your example,
- Halley's Comet was the first period comet known (designated 1P) and this apparition was the first seen in "half-month" U (the first half of November) in 1982 (giving 1P/1982 U1)
- the third comet past perihelion in 1986 (1986 III)
- the 9th spotted in 1982 (provisional designation 1982i)
- E&OE. HTH. -- ALoan (Talk) 23:54, 15 January 2006 (UTC)
