Talk:Comet

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Hill sphere dimensions - very outdated[edit]

The article gives a size of 230,000 AU for the Hill Sphere of the Sun, but the reference it cites for that is a a 1964 Paper by Chebotarev. That's very old, and as it depends crucially on the estimated mass of the galaxy - an estimate that's changed greatly with advances in astronomy and astrophysics in the nearly half century since that paper was written. That paper is reproduced in English here - the relevant section is section 6 "solar gravitational sphere", pp621-622 of the original journal. There Chebotarev says "For the mass of the galaxy we assume the value M=1.3 × 1011 solar masses." And indeed if one runs that through the formula given for a simple (non-eccentric) system given at Hill sphere, one gets a value for r of 225837 AU (with the value for the semimajor axis Chebotarev cites); that's consistent with the 230,000 value he gives. --165.155.196.123 (talk) 20:12, 7 November 2011 (UTC)

That paper is 46 years old, and it looks like the current estimates of the galaxy's mass are quite different. Looking first at Wikipedia's numbers - Milky Way says its mass is roughly 1.4×1042 kg, and the Sun article says its mass is 1.9891×1030. Going by those figures, the mass of the galaxy is 7.038×1011 solar masses, making the galaxy 6 times more massive than Chebotarev's numbers. Running that through the equation (with a slightly refined value for a, again from Sun) gives us a Hill radius of 130,261 AU (down from Chebotarev's 230,000).

But there's more. If you ask Wolfram Alpha for "mass of the galaxy" it says 6×1042 kg which it says is "based on 2009 velocity data from Mark Reid using the Very Long Baseline Array (VLBA)" (I guess that's the finding discussed here). That gives us a mass ratio of 30.2×1011, making the Hill radius about 80,000 AU - that's about a quarter of Chebotarev's number.

Moreover, ask Wolfram Alpha "distance from the sun to the centre of the galaxy" and it says 2.349×1020 m (it cites a bunch of astronomical sources). That's quite a bit lower than the values given by Wikipedia or Chebotarev; plugging that into the equation and we get an estimated Hill radius of 75,350, a third of Chebotarev's number.

I'm not proposing that we use the numbers from my calculation, but it does look like Chebotarev's calculation is based on a very wrong estimate of galactic mass. We need a modern reference with a calculation based on modern observations. -- Finlay McWalterTalk 18:49, 16 January 2011 (UTC)

I used Gillessen2009 for the distance to our galactic center as 8.33 kiloparsecs (27,200 ly). I have done some Wikipedia work using barycentric coordinates for the apoapsis distance of bound comets listed at non-periodic comet. I notice that JPL Horizons shows Comet West has a barycentric apoapsis distance (AU) of "AD= 6.977038306313576E+04 (epoch 2031-Jan-01)" (~69770AU). That is very close to your suggested number. Unbound comets seem to travel out to 10^91 AU. I certainly agree that we need a more recent reference for the solar hill sphere. Besides, I would really like to know how close Comet West is to the edge. -- Kheider (talk) 02:54, 2 February 2011 (UTC)

Spacecraft Imagery[edit]

Some spacecraft photos of some nucleuses with dust or particles jetting out would be a nice addition.--Tablizer (talk) 05:37, 16 February 2011 (UTC)

Contradiction tag[edit]

The following has been cutNpasted from the contradiction tag in the article for better exposure here: "reason = Contradicts following statement (and statement made in the intro) that a few comets are permanently (mathematically) thrown out of the Solar System after a single (observed) pass. Also contradicts literal meaning of "single apparition". The explanation seems muddled about extremely long period vs single-apparition comets. (kheider notes: Readers may be confused by difference of Parabolic is e=1 and Hyperbolic is e>1. I may remove this whole sentence and comment as redundant.)" (I am not the author of the tag.) --S. Rich (talk) 02:02, 23 February 2011 (UTC)

Yes, that section needs a clean-up. The problem is that there is a very small difference in overall velocity of a comet like Comet McNaught that should return in ~92,600 years (semi-major axis=~2050AU) and a comet like C/1980 E1 that should get lost beyond the Oort Cloud (>80,000AU or so). The Osculating perihelion eccentricity is never a good indication whether a comet leaves the solar system since often the osculating eccentricity is larger than 1 in the inner solar system, but the future (or proper) eccentricity is smaller than one when it gets beyond the influence of the planets. I have been slowly trying to build-up List of non-periodic comets and Barycentric coordinates (astronomy) so that there might be some good sub-articles and references to pull from. But we still need more references. -- Kheider (talk) 03:04, 23 February 2011 (UTC)

List of Visible Comets[edit]

I think that a "List of Visible Comets" (i.e. of above Mag 6), in order of date of greatest brightness, would be of use. If it would be too long, make it a "List of Easily Visible Comets", with a cut-off of Mag 3 or 4. 94.30.84.71 (talk) 13:00, 3 May 2011 (UTC)

I think this page use to have such a thing. But unless it is updated ever month, it would quickly become dated and incorrect. Such information can be located at: http://www.aerith.net/comet/weekly/current.html -- Kheider (talk) 15:41, 3 May 2011 (UTC)

Distance from the sun[edit]

There is no average distance from the sun listed. If an expert could do this it would improve the article--174.34.41.239 (talk) 13:55, 14 June 2011 (UTC)J28

There is no average distance to the Sun because comets like 2P/Encke take 3.3 years to orbit the Sun, while comets from the Oort Cloud can take upwards of 30 million years to orbit the Sun. -- Kheider (talk) 16:11, 14 June 2011 (UTC)

Recent comets documented at Flickr[edit]

Upon a cursory search at Flickr to see what comets have recently been easily visible, I came up with:

I was also reminded of how confusing the difference between a comet and a meteor can be, because pictures of them are so similar. Lots of pictures of meteors came up under a search for comets, so it's apparent that folks really don't know the difference. I've never seen a comet, and I would've flown to New Zealand to see McNaught, if I had known about it. Heyzeuss (talk) 13:59, 8 August 2011 (UTC)

You might be interesting in Brightest comets seen since 1935 (International Comet Quarterly). -- Kheider (talk) 17:54, 9 August 2011 (UTC)


Page protection?[edit]

Based on all the recent vandalism, I think it is time to protect this page. -- Kheider (talk) 18:51, 15 November 2011 (UTC)

Comet components[edit]

NASA diagram of comet components from a few years back.

I found this diagram and scanned it in hopes that it could be useful, but I do not know the state of comet studies to know if it's still accurate. If it's still accurate, I think it or a re-drawing in SVG could benefit this article. -- ke4roh (talk) 01:10, 15 April 2012 (UTC)

Families[edit]

After Jupiter family comet was redirected to the orbital section here, I read the section with displeasure, even a smidgen of dismay. It does not seem well organized. It does not proceed as clearly as I would like, from general to particular types of orbits, and the division between long and short periods is handled by two very long paragraphs, each in a bullet point which to my understanding is a method best used for long lists of short texts, often without a full sentence and seldom with enough sentences to make a paragraph. For example, illustrative lists of prominent comets belonging to each class would each be a bullet list, following the definition and discussion of each class, each in its own subsection.

The types of orbit, seems to me, ought to be in sequence from infinite through long to short, following the most accepted hypothesis of how they might migrate. Unless, that is, my topical ignorance is making me jump to unaccepted conclusions. This scanty topical knowledge is making me wary of changing anything, since my addition of an external link to a professor's article that mentions capture to shorter orbit may have filled a void but probably compounded the problem of poor organization. Are my concerns entirely due to ignorance of the topic, or is my feeling justified and the section ought to be reformed? Jim.henderson (talk) 02:39, 13 July 2012 (UTC)

Comet orbits can migrate in or out just like a centaur. Very few comets are on a true infinite orbit since you need to calculate the barycentric solution after the comet has left the region of the planets. Most orbital solutions are a generic (unperturbed) two-body solution calculated when the comet is near perihelion.
It would be good have a section defining different families. Jupiter Family Comets (JFCs) can have (2 < TJupiter< 3), or the more classical (generic) definition of (P < 20 y). We could define Halley-type comets as (20 y < P < 200 y), Encke-type comets as (TJupiter > 3; a < aJupiter), and Chiron-type comets as (TJupiter > 3; a > aJupiter). -- Kheider (talk) 04:24, 13 July 2012 (UTC)

Sounds good. Remaining question is, should someone who knows the topic well do it, or someone who doesn't? Jim.henderson (talk) 01:51, 14 July 2012 (UTC)

I have populated Category:Halley-type comets and Category:Encke-type Comets as a starting point. -- Kheider (talk) 22:12, 26 July 2012 (UTC)
Unexpectedly few editors are participating. Anyway in editing the article I went conservative, adding only two broad subheads rather than a narrower one for families. Others may think a further division of those subsections would clarify these matters further. I also gave the new categories a parental cat; ought they also have an orbital parent? Jim.henderson (talk) 18:28, 28 July 2012 (UTC)
There are the orbital types (Quasi-Hilda comets, Halley-type, etc.) and then there are the fragmented families from a parent body such as Schwassmann–Wachmann. I have just focused on the orbital types for now since types can be applied to any comet. -- Kheider (talk) 13:19, 29 July 2012 (UTC)


I was curious about the difference between asteroids and comets and ended up at this page. Most of the article seems well written and informative. However the whole section on Single-apparition comets is completely unreadable to a non-astronomer. Other things I find on the web it say they are comets with extremely long orbits, but here its just a mess of highly technical astronomical terms. It seems that even if I could understand it, its just a collection of facts with no logical flow or purpose. Someone who knows more about it than I do might want to add a sentence or two of explanation in plain english and trim out some of the nonsense. — Preceding unsigned comment added by 24.228.216.249 (talk) 04:32, 13 August 2012 (UTC)

Overusage of 'by'[edit]

The text to the image of 103P/Hartley with jets is rather unclear, IMHO:

Nucleus of Comet 103P/Hartley with jets streaming out by a visiting space probe.

The most grammatical interpretation would be that the jets were caused by the space probe. However, I found the original contribution here, and it makes two things clear: That the contributer at the time was more interested in providing good illustrations than good grammar (cf "It is about 2 km in long 400 meters wide..."); and that (s)he repeatedly used "by" for denoting the photographer. Thus, the same should hold for this image, and I'll change the text accordingly. JoergenB (talk) 20:28, 23 February 2013 (UTC)

History of study/ Is not complete[edit]

There are some theories from Ali Ibn Abu Talib (7th century AD)that should be mentioned. As we read theories about comets from Aristotle and others that are not accepted any more maybe it is necessary to pay attention to some old theories that are proved nowadays. One of them is Ali's theory about dimension of nucleus and tails and also about the population regions of the comets. These theories are documented in some reference books as follows:

تفسير نور الثقلين ج‏2 ص 36

 تفسير القمي ج‏2 ص14
بحار الأنوار (ط - بيروت)  ج‏55 ص 113 
البرهان في تفسير القرآن ج‏4 ص 145 

مجمع البحرین- الشیخ الطریحی- مطبعة الآداب- النجف الاشرف- المجلد الثانی ص 162

He has said about the nucleus: "The comets are like the biggest mountain on the Earth." This theory is now proved by models and observation. Also he has said about the tail and population regions that: "These stars that exit in the sky have cities like the cities on the Earth that every city corresponds to two columns of light, the length of these columns in the sky is equal to a path of 250 years." For your information, a horse can run with mean speed of 48 km/hr and this is the fastest method for traveling in that time. So a horseman can travel more than one hundred million kilometers if he rides continuously for 250 years. It seems that the cities mean the population regions that nowadays scientists have found them in the Kuiper Belt and Oort cloud. — Preceding unsigned comment added by Smyeganeh (talkcontribs) 15:13, 5 April 2013 (UTC)

Dirty Snowball[edit]

Can anyone confirm that the term Dirty Snowball, used twice on this page, each using tabloid journalist quotes thus: "Dirty Snowball", was coined during the Giotto flyby by an American with a 'sour grapes' attitude? Can anyone name the american? 91.125.28.82 (talk) 11:08, 9 April 2013 (UTC)

The oldest reference I could find to the colloquialism 'dirty snowball' was 1960. By 1963 it was being ascribed by various sources to Fred Whipple. I didn't see it in his 1950 comet papers, so presumably he used it informally while talking to the press or the public. Praemonitus (talk) 18:06, 31 August 2013 (UTC)

Proposal[edit]

I propose moving some history, of which there is possible to much, to a new article, and getting all the science - separate articles like comet nucleus and Coma (cometary) - back here, as they contain little information not in the main article. That also makes it easier for me to get this article up to a good standard of verifiability, as history is much harder to source than science. Jamesx12345 21:50, 20 August 2013 (UTC)

GA Review[edit]

This review is transcluded from Talk:Comet/GA1. The edit link for this section can be used to add comments to the review.

Reviewer: Chiswick Chap (talk · contribs) 18:17, 22 September 2013 (UTC)

I will be pleased to review this article. Chiswick Chap (talk) 18:17, 22 September 2013 (UTC)

GA Table[edit]

Rate Attribute Review Comment
1. Well-written:
1a. the prose is clear and concise, it respects copyright laws, and the spelling and grammar are correct. Prose: good; copyright: seems ok; spelling: ok; grammar: ok
1b. it complies with the manual of style guidelines for lead sections, layout, words to watch, fiction, and list incorporation. Lead: see comments; layout: ok; weasel: ok; fiction: n/a; lists: Spacecraft targets is not too long to stay, could be hived off as a list article. Probably needs citations.
2. Verifiable with no original research:
2a. it contains a list of all references (sources of information), presented in accordance with the layout style guideline. ok
2b. all in-line citations are from reliable sources, including those for direct quotations, statistics, published opinion, counter-intuitive or controversial statements that are challenged or likely to be challenged, and contentious material relating to living persons—science-based articles should follow the scientific citation guidelines. See comments.
2c. it contains no original research. ok
3. Broad in its coverage:
3a. it addresses the main aspects of the topic. See comments.
3b. it stays focused on the topic without going into unnecessary detail (see summary style). ok
4. Neutral: it represents viewpoints fairly and without bias, giving due weight to each. No sign of POV.
5. Stable: it does not change significantly from day to day because of an ongoing edit war or content dispute. No problem.
6. Illustrated, if possible, by images:
6a. images are tagged with their copyright status, and valid fair use rationales are provided for non-free content. All from Commons.
6b. images are relevant to the topic, and have suitable captions. Ok, possibly somewhat many.
7. Overall assessment. A well-rounded, informative and well-sourced article.

Comments[edit]

  • Some claims are uncited and most likely need to be. I'll mark up the ones that need attention. It may be these can be handled just by copying one of the earlier refs to indicate which one is the source.
  • There are however refs in the lead; if any claims are made there which are not in the body of the article, they should be moved there. The lead itself should summarize the article, most likely roughly reflecting the structure its main sections.
  • Who says something is an 'unusual comet'? Section may need to be clarified, with a source for the claim. If 'unusual' is actually a rag-bag for different things - orbital shape, or being seen to break up, or striking a planet - then it might be better to talk about those things separately?
  • And phrases like "very unusual" are probably WP:POV; if from a RS, provide quote and ref, otherwise remove.
  • 'Early observations and thought' names nobody before Brahe. Ian Ridpath names Pliny, Aristotle, Ptolemy, and Seneca all of whom had something interesting to say about comets. It might be worth quoting (and wikilinking) these authorities, or at least explaining what they thought on the subject (and perhaps mentioning how influential they were, right through to the middle ages).
There is indeed a great deal of fascinating stuff - I would commend Sagan & Druyan - but because of how much there is, I created Observational history of comets with what I removed from the article. I could just merge it back, but I think that because comets have such a fascinating social history, almost completely separate from their scientific aspects, there is scope for a second article. Jamesx12345 19:37, 22 September 2013 (UTC)
There should be a brief 'summary style' account of the early observations and thought, collapsing the classical authorities - Aristotle, Pliny especially - into one or two sentences. Actually the other article doesn't mention Pliny either (and it should). Chiswick Chap (talk) 13:02, 23 September 2013 (UTC)
  • 'slammed into Jupiter's atmosphere' - 'impacted' (or similar word) would be more neutral, less comic-strip.
Will fix.
  • Not critical for GA, but why are new refs being added in Harvard style when many old ones are not in that style? Generally one shouldn't change ref style, nor mix.
If there are two or more references to a book, I tend to use harvnb, as that makes it shorter, but when a book is used just once I simply cite it as I would a journal. It looks better when more than one book is cited more than once.
Mm. Doesn't matter here but would likely cause a tangle at FA.
  • "Flyby" in table entries does not seem to add any information. Perhaps remove.

Tunguska event[edit]

A 2010 study seems to agree that the Tunguska_event#Asteroid_or_comet was in fact a comet. I will let the regulars here decide on inclusion. I was amazed that I didn't find mention of it in this article. Meteorite mentions it twice and perhaps needs clarification regarding the newer study.--Canoe1967 (talk) 19:27, 24 September 2013 (UTC)

I've added something - there appears to be a lot of debate between both scientists and tin-foil hat types. Jamesx12345 19:42, 24 September 2013 (UTC)
It looks like the GPR in 2010 was done by proper science. The source states it is now confirmed as a comet which we may wish to note. "Pravda states it is now confirmed as a comet." or similar. I also think we should include the Tesla bunk. Even though it is a wild unproven theory our readers still deserve mention of how it came about and how it was shot down. I don't think I will get involved in that wiki-drama much though.--Canoe1967 (talk) 20:01, 24 September 2013 (UTC)
Pravda? They said the world was going to be invaded by flying saucers last year. As I recall, the consensus is largely that it was an asteroid airburst. Comet impacts with the Earth are extremely rare, even by impact standards. Serendipodous 20:27, 24 September 2013 (UTC)
It is not known for certain if it was a comet or an asteroid. Leave the Tesla rubbish out (WP:UNDUE). -- Kheider (talk) 22:11, 24 September 2013 (UTC)

Contrasting RS's: tidal forces and comet breakup[edit]

Current article reads "Comets are suspected of splitting due to thermal stress, internal gas pressure, or impact."[1]

However, BBC reports in 2013:

"...The Sun's intense gravitational field produces tidal forces that will also have a major effect on the comet."[1]

Any experts here who can provide advice? Would it be non-controversial to merge them into "Comets are suspected of splitting due to thermal stress, internal gas pressure, tidal forces, or impact."? Rolf H Nelson (talk) 23:26, 2 December 2013 (UTC)

  1. ^ Boehnhardt, H. (2004). "Split comets". Comets II: 301. Bibcode:2004come.book..301B.