Talk:Comet/Archive 1

Archive 1

Miscellany

There's another comet paper at Comets, which needs to be intregrated with this one. --Zundark, 2001 Oct 14

Drat, should have checked before I wrote all that stuff. :) I'll get to work on it. -BD

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This page could really use a ordinary picture of a comet, preferably one showing two tales. And maybe a picture of the Jupiter impact. Should be something we could use at NASA. I just can't ever find what I want there. Rmhermen 17:04, Mar 5, 2004 (UTC)

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"Some modern Freemasons claim that Stonehenge and similar ancient observatories were used to evaluate whether comets would hit the earth."

Why "modern Freemasons" nobody else can believe it ? This need some explanatio/sources IMO. Ericd 12:10, 18 May 2004 (UTC)

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Hmm. Gonna get meself in more @hit here.

Not everyone was surprised by the discovery of X-rays. One astronomer named Jim McCanney actually predicted them. He did so as early as 1981 in a scientific paper first published in the journal Kronos. McCanney even urged NASA officials to look for X-rays when the agency was preparing a fly-by of Comet Giacobini-Zinner in 1985. At the time, NASA's ISEE-3 satellite had already completed its original mission, and was being reprogrammed for comet study. The spacecraft had X-ray equipment on board, and McCanney urged NASA to use it. Instead, NASA shut down the equipment to conserve power. NASA's experts concluded that there was no point in leaving the X-ray detector on, since there couldn't possibly be X-rays coming from a cube of ice.[1]

Noting that McCanney is clearly what Wikipedians in good standing (which I am not) class as a cuckoo, I have two simple questions: was such an article published; did NASA get requests to check for X-rays? Kwantus 05:39, 2005 Feb 1 (UTC)

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Should there be something about near-earth comets that may pose a collision danger? According to the Near-Earth object article, at least 49 near-earth comets have been identified... (2005, Jul 6)

Request for references

Hi, I am working to encourage implementation of the goals of the Wikipedia:Verifiability policy. Part of that is to make sure articles cite their sources. This is particularly important for featured articles, since they are a prominent part of Wikipedia. The Fact and Reference Check Project has more information. Thank you, and please leave me a message when you have added a few references to the article. - Taxman 17:36, Apr 22, 2005 (UTC)

Proposed Edition

The text that follows is my proposed edition to this article. If anybody has a problem with it, identify it before I make the changes to the article.

For other uses, see Talk:Comet/Archive 1 (disambiguation).

A comet is a small astronomical object similar to an asteroid, hypothesized to be composed largely of ice. Unlike asteroids, comets typically move in highly elliptical orbits, the aphelia of which may be many times more distant than Pluto's orbit. Often described as "dirty snowballs", or, after the "Deep Impact" mission, "snowy dirtballs", comets are commonly believed to be composed largely of frozen carbon dioxide, methane and water with dust and various mineral aggregates mixed in.

Comet Borrelly exhibits jets, yet is hot and dry.

As late as 2002, no conclusive evidence of water had been discovered on any comet. NASA's Deep Space 1 team, working at NASA's Jet Propulsion Lab, obtained high-resolution images of the surface of comet Borrelly. They announced that comet Borrelly exhibits distinct jets, yet has a hot, dry surface. NASA remains confident the water is hidden just beneath the "crust". The assumption that comets contain water and other ices led Dr. Laurence Soderblom of the U.S. Geological Survey to say, "The spectrum suggests that the surface is hot and dry. It is surprising that we saw no traces of water ice."[2]

Comet Wild 2 exhibits jets on lit side and dark side, stark relief, and is dry.

This surprise was echoed in 2004, when comet Wild 2 was visited by NASA's Stardust spacecraft. Claudia Alexander, a program scientist for Rosetta from NASA's Jet Propulsion Laboratory who has has modeled comets for years, reported to space.com about her astonishment at the number of jets, their appearance on the dark side of the comet as well as the light side, their ability to lift large chunks of rock from the surface of the comet and the fact that comet Wild 2 is not a loosely-cemented rubble pile. In addition, no ices were identified on Wild 2.[3]

Comets are believed to originate in a hypothetical and as yet unobserved cloud (the Oort cloud) at large distances from the sun consisting of presumed debris left over from the condensation of a hypothetical solar nebula; the outer edges of such nebulae are assumed to be cool enough that water would exist in a solid (rather than gaseous) state. Asteroids are believed to originate via a different process, but close inspection of comets has revealed no water ices or volatiles, and show that comets appear to be very much like asteroids.

Hmm, well, what was wrong with my edits? I think I presented both POVs correctly. If you wish, you may add a reference to the section in the introduction but having so much disputed information in the intro seems to push it off balance. Also, the scientific community at large still believes comets are made mostly of ice and at the beginning it say "are believe to originate" etc. which is good enough. I think my edition is more balanced, however, you of course are entitled to disagree. User:Sasquatch

I checked the page again and saw that the information I put in was kept mostly intact, only moved. I still think the thrust of it, that data suggests comets have very little, if any, ices or volatiles, should go in the opening paragraphs. The opening paragraph still gives the reader the impression that comets are made of these ices and volatiles, but observations show ices and volatiles are present in miniscule amounts if they're present at all. I'm going to move some stuff over here from my talk page to support this. Plautus satire 14:33, 29 July 2005 (UTC)

This proposed version puts way too much emphasis on the issue of water detection, especially considering that the general consensus in the scientific community is pretty clear. Deep Impact was only a month ago, that's not enough time to claim that comets are now commonly called "snowy dirtballs" rather than "dirty snowballs" (a phrase that goes back decades). In general, there are too many weasel-words being used here. I think Sasquatch's version cleared up all these problems nicely. Bryan 06:27, 28 July 2005 (UTC)

I'm going to move some stuff over from my talk page that demonstrates again and again astronomers changing their views about specific comets being made primarily of ices or volatiles. Plautus satire 14:33, 29 July 2005 (UTC)

In the picture (which is now on the Article page) of Comet Borrelly, what do the colors represent? I assume temperature, but the picture needs a scale. Mcswell 18:51, 25 February 2007 (UTC)

"close inspection of comets has revealed no water ices or volatiles" I'm not sure this is correct. Have just read the ESA page on Giotto http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=31878, in which it is clearly stated that about 80% by volume of all the material thrown off comet Halley is water, as detected by Giotto. Also I really think this image http://giotto.esa.int/science-e-media/img/3c/i_screenimage_26428.jpgotto needs to go on the page somewhere, not least for it's historical value as humanities first close up image of a cometary nucleus. User:Gazzarrr 3rd. August 2008. —Preceding undated comment was added at 16:11, 4 August 2008 (UTC)

Creationism section

Although contrary to my previous position on this issue, having come across this at least three times in my WikiTravels (recently on Talk:Oort cloud), it is clear a significant number of creationists believe the fact comets are around (and according to them have no natural source) confirms young earth creationism. As such I think a "Creationism" section outlining the argument, linking its primary source Walt Brown, and a short rebuttal is appropriate. - RoyBoy ⁸⁰⁰ 18:37, 30 November 2005 (UTC)

As discussed in that talk page, this is not really needed in the Oort cloud article and in this one. It fits just fine in the article about the author, Walt Brown, but is not "mainstream" enough IMO to have its own space here. Awolf002 20:31, 30 November 2005 (UTC)

Alrighty, you won't get an argument from me. It does get tiresome to address these issues and have nothing to point to, in order to say, its there and has been addressed. I guess I should indeed do something about that in Walt Brown. - RoyBoy ⁸⁰⁰ 00:26, 1 December 2005 (UTC)

Done. - RoyBoy ⁸⁰⁰ 01:44, 1 December 2005 (UTC)

I do not believe that an explicit creationism section is appropriate as under the Wiki's guidelines it does not reflect a world view of the subject. At most it should fall under the influences on culture section. I do not believe that we should encourage the view that creationism is in some way important enough that it deserves it's own section over and above the creation myths of cultures other than those effected by the Abrahamic religions. —Preceding unsigned comment added by Gazzarrr (talk • contribs) 12:41, 28 October 2008 (UTC)

Pulp fiction

"Deeply implausible"? It was written in 1877! And I suppose a meteor shower rendering people blind is plausible? I'm deleting. Trekphiler 04:37, 23 December 2005 (UTC)

Improvement drive

Asteroid deflection strategies has been nominated on WP:IDRIVE. Support it with your vote if you want it to be improved.--Fenice 22:45, 29 December 2005 (UTC)

Etymology

I am including information about the origin of the word "comet" (Gr. "kometes", Aristotle.) CurtLindsay 2005.02.03 22:08 PST.

Comet symbol

Do we really need to have it in the opening sentence? it hardly seems important enough, many users will see it just as a question mark, and I'm not even sure it's very commonly used anyway - I've never seen it myself before, in the literature or elsewhere. I'm sure it could be included lower down though. Worldtraveller 12:59, 12 February 2006 (UTC)

I'd agree with that. There seems to be a tendency to use the lead as a bin for anything miscellaneous, which is roughly the opposite of what it should be. It's also very misleading, since I would read it as saying that the symbol in question is a question mark- we need some cunning way of saying otherwise. Mark^{your words} 13:10, 12 February 2006 (UTC)

Yes, put it into the last section of the intro paragraph. I would have done that already, but I just see a question mark, so I can not tell if I mess things up moving the text. Awolf002 13:12, 12 February 2006 (UTC)

I suggest keep, the symbol is widely known, and for users read it as a question mark, it's their own problem, they should configure their computer properly first. — Yaohua2000 19:34, 12 February 2006 (UTC)

No-one's suggested deleting it. Mark^{your words} 20:17, 12 February 2006 (UTC)

I suspect we could interpret Worldtraveller's deletion of the character as a suggestion that it should be deleted. :) Bryan 21:03, 12 February 2006 (UTC)

To help editors, at least, we could replace the character with its HTML unicode entity: ☄ (☄). Bryan 19:14, 12 February 2006 (UTC)

THE COMA IS LIGHT!!!

The statement saying that the comas would be made from dust and gases is more than funny. Think about how fast would such a comet consume if it would liberate dust and gases behind it. No, people! Comets don't leave dust and gases behind it. THE COMETS PRODUCE LIGHT, due to one of the natures laws veritable for all the quickening bodies: ANY BODY PRODUCES ELECTROMAGNETIC FIELD IN OPPOSITE TO ITS ACCELERATION. The properties of this field depends on the properties of that body and its movements. I can not find, the frequency of the light produced by the comets, yet, but I am convinced that it is an universally phenomenon. This theory says that even all the planets (mostly Mercury) has an opposite tail to the Sun, but this one is probably made from microwaves because the acceleration of the planets is smaller than comets. Even the radioactivity of the atomics kernels is due to this universally phenomenon! abel 15:46, 21 April 2006 (UTC)

This is the wrong place to propose new (and unorthodox) theories (dubbed original research in WP). Please, find a venue on a different web site for this type of discussion. Awolf002 22:53, 21 April 2006 (UTC)

Thank you for response. But NOT EXIST other place to propose new theories! And this text is JUST DISCUSSION for THIS place. abel 06:02, 24 April 2006 (UTC)

Not quite. This place/text is meant for discussing the article and possible improvements. So, when proposing such an improvement one should follow accepted policies, and your suggestion runs into WP:NOR. Therefore, I think you want to find a different website altogether to discuss your ideas. Awolf002 01:00, 25 April 2006 (UTC)

This is the most obsurd thing I have ever heard except for the folks that thought there was a space ship behind Hale-Bopp. —Preceding unsigned comment added by [[User:{{{1}}}|{{{1}}}]] ([[User talk:{{{1}}}|talk]] • [[Special:Contributions/{{{1}}}|contribs]])

Most sources say that the coma's brightness comes from the reflection off the coma's dust and gas. The coma is not completely behind the comet, as a huge portion in in front of its acceleration. Also, if the coma was microwave energy, it would not be visible. The comet does, however, emit ultraviolet light, hydrogen, and X-rays, and this is mostly caused be the solar wind's effect on the comet. Also, the tail of the comet is dust and gas and the reflection of it, and so is the coma. It's not impossible that the coma emmits a bit of light, since there is some effects on the comet that cause it to emit energy, especially of high frequency. Actual light emitted directly from the coma, however, has not yet been observed. AstroHurricane001 00:38, 21 November 2006 (UTC)

Wikipedia:Version 0.5 Nominations

This article was selected for inclusion in Version 0.5 due to its quality and its importance; however, is it possible for the reference numbering to be fixed? Titoxd^{(?!? - help us)} 06:27, 31 May 2006 (UTC)

Confirmation of water

Deep Impact confirmed that Tempel 1 at least has large amounts of water ice below the surface, though not much on it, since it would obviously be vaporised by the sun. I'm rewriting some things to reflect this.--Planetary 23:58, 18 August 2006 (UTC)

what is the next big one?

I realize it's not 100% possible to predict, but when will be the next great or significant comet to look out for? I don't want to miss it. Or I wonder how long I have to wait. (I live on Earth.)--Sonjaaa 02:15, 19 August 2006 (UTC)

Halley will be back in 2061, other then that, I don't know.--Planetary 02:45, 19 August 2006 (UTC)

That's actually a good way of putting it. The short-period comets, those with orbital periods less than 200 years or so, we can more or less predict their positions, but of them, only Halley consistently puts on a good show. Most of the really bright comets are long-period comets, that have never appeared before within human history, and we have no idea when one is coming until someone notices it. Shimmin 02:53, 19 August 2006 (UTC)

So if a really bright comet suddenly came, we would only get notice a month or so notice before it's visible? Or how long before it comes is it usually predictable?--Sonjaaa 04:25, 21 August 2006 (UTC)

It depends on how early the comet is detected and the comet's orbit. A number of automated telescopes, that are used for NEO searches, sometimes discover long period comets when they are very faint. Comet C/2002 T7 LINEAR was discovered when it was 17th magnitude and astronomers had almost two years before it reached perihelion. ~ User:LawfulGoodThief 06:03, 26 August 2006 (UTC)

I think the current visible comets section needs to be frequently updated. It is now November, not October. AstroHurricane001 00:41, 21 November 2006 (UTC)

"Dave's Virtual Sungrazing Observatory"

The newly added text with the 'advertising' for this web site is superflouos and it should go. This is not an article about how to find comets. Adding a link this is inappropriate. Awolf002 16:32, 3 December 2006 (UTC)

Comet NEAT

Hi. Is there an article on Comet C/2002 V1? Yes, it's notable, and I am able to provide reliable sources. Please respond so I could decide whether or not I create the article. Thanks. AstroHurricane001 23:23, 30 December 2006 (UTC)

Ok, I guess I'll just create one Here. I know where to find references. AstroHurricane001 23:10, 1 January 2007 (UTC)

Great comets

How bright does a comet have to be before it is classified as a great comet? Is mag. 0 to -7 bright enough? Thanks. AstroHurricane001^{(Talk+Contribs+Ubx)} 21:10, 12 January 2007 (UTC)

"Wide" Page

Is it just me or is the page very "wide?" Mike6271 03:24, 22 February 2007 (UTC)

Looks fine to me. Might just be your personal computer settings. Serendipodous 04:45, 21 March 2007 (UTC)

No he's right the page was too wide because some mentally challenged person decided to put a truckload of random letters together and create a wide page, slowing our computers down in the process. However, I have taken the initiative to delete that, and if you (mentally challenged person) are reading this, I suggest you stop and read the text above the edit screen, because it states there that we have your IP address in storage and can track you down. User: yctaabpjic 11:25, 4 June 2007 (PST)

• Tsk, tsk... A little harsh on the "we'll track you down" bit! Don't WP:BITE / threaten the newbies! Assume Good Faith (for all you know, it could have been some weird errant mistake). A gentle, guiding hand will be fine. Thx... That said, vandalism (the edit in question probably qualifies) is also a no-no. So tsk, tsk, to them too! Let's all just get along... *wink* Mgmirkin (talk) 00:47, 29 January 2008 (UTC)

Confused by this sentence

"One theory holds that as a comet approaches the inner solar system, solar radiation causes part of its outer layers, composed of ice and other materials, to melt and evaporate, but this has not been proven."

What other theories are there? How is this theory still in debate, even after we've sent probes into the comas of several comets? Serendipodous 04:44, 21 March 2007 (UTC)

Do you really want to open that can of worms? 'Cause there *are* alternatives. Strangely enough, recent Stardust results 1 2 3 4 5 appear to support their assertion that comets are "just another asteroid" with some caveats. Doesn't necessarily prove them right. However, it's "interesting." Something to keep an eye on. But, we'll just say I don't plan to put it into the main article any time soon, for fear of the inevitable witch hunt that would ensue (frankly, I'm loathe to even mention it for that reason). Mgmirkin (talk) 00:56, 29 January 2008 (UTC)

Do comets shrink?

Comets trails are made by getting too close to the sun and bits burning off, right? Are they constently shrinking? Are they replenished somehow or will they eventually shrink down to nothing?--Viridis^{talk|contributions} 06:07, 9 April 2007 (UTC)

Well, comets don't "burn" if you mean the chemical process. Instead their tails are formed by water vapor, dust etc. Comets can't replenish their material, so every time they come into the inner Solar System they indeed lose some material. After thousands of orbits a comet has lost all its volatile material and it becomes a "dead comet". Many near-Earth asteroids may have been originally comets.--JyriL ^talk 12:32, 9 April 2007 (UTC)

Motion & velocity

I have some questions regarding the above, it is not exactly clear from the article. How exactly do comets start to move, gain speed while approaching the sun, and loose it again when moving away from the it?

For example the outer cloud is only weakly bound to the Sun, but still rotating slowly, therefore it has some initial speed. So I presume a future comet has to be influenced by another object, making it move outwards of it's natural rotation in the Oort-cloud. Or is it caught by the gravity well of the Sun, and then pulled towards it?

Secondly, if moving towards the sun or jupiter, how does the comet's speed increase? I'm quite puzzled that mademade rockets are unable to push it beyond 17.5 km/s (Voyager 1), while comets can gain speeds up to 50 or 60 km/s, even without active propulsion. A comet doesn't have have some kind of propulsion, so the increase in speed can only be from gavitational pull, or am I mistaken?

thirdly, at perihelion the speed of a comet is about 500,000 km/h, but at aphelion it has slowed to only a few thousand km per hour. How it this possible? I can't think of what should slow it down in a near vacuum, except for some roaming dust. Evenmore, as the comet is moving away from the sun, shouldn't it actually gain speed, as the gravitational pull of the sun becomes weaker the further it travels? Or is it actually this pull that slows it down ;) I'm confused since the Voyagers and Pioneers have reached escape velocity, but comets (who appear to have a greater speed) do not? Comets appear to obtain great speeds at ease, even if their nucleus has a diameter of 50 km. So I'm wondering why or rockets can't. Thanks to the one(s) that can give some enlightment! --Patrick1982 10:20, 20 August 2007 (UTC)

Wow there is a lot in there to answer. The overall answer though is its all the sun's gravity doing the work.

It's peturbations by other object that set a comet on a path to the inner solar system. It could be orbiting the sun for billions of years and then finally pass quite close to another object sending one, the soon to be comet, on its way towards the sun. Now, remember what newton said? An object won't change speed unless a force is acting upon it. The object was already moving at a slow rate and now begins to fall towards the sun... and fall... and fall... and fall possibly for hundreds if not thousands of years. All the time it is falling it is accelerating as gravity is acting upon it, weakly at first but growing in strength all the time. It reaches its max velocity as it passes its closest point to the sun then the forces go into reverse - now gravity will no longer speed the comet but slow it as it moves away. Two things can happen now - either the comet can fly off into space and never be seen again like Comet McNaught or it can continue to orbit the sun as many comets do, like Halley's Comet. Now - let's compare to Voyager etc. While a comet reaches it max velocity close to the sun where it will also face the full braking effect of the sun's massive gravity as it moves away voyager reached it maximum speed way out by Jupiter, where the sun has a lesser hold. The Sun's gravity still slows voyager down every day - just a tiny bit, as it does to a comet all the time it moves away. Now escape velocity is an interesting thing... and its not a constant. It depends on where you are and the path you take. If we assume the sun isnt moving (which it is) a path directly away from the sun would require a higher escape velocity than a path at a tangent. And of course the further away from the sun you start the lower speed you need to escape. So 17km/s out past Jupiter may well be an escape velocity, but 50 or 60 km/s near the sun might not be.

Now gravity and rockets work to accelerate things quite differently. A rocket has a fixed ammount of energy - it can accelerate a mass to a given speed, or twice that mass to half that speed etc. Gravity doesnt care how heavy an object is it will accelerate it at a rate that depends only on how far away it is. Voyager has been travelling for 30 years or so now... and in all that time its rocket engines only fired for a couple of minutes. For the whole of the rest of the time it has been accelerated (and decelerated) by gravity. It has gained more momentum from gravity than any rocket we could build could have given it. How did it gain speed from gravity rather than just being slowed down? Well that was due to clever use of the alignment of the planets and getting a "gravity assist" from each one to the next.

It was realised a long time ago by Kepler that in eliptical orbits a line joining a planet and the sun sweeps out equal areas during equal intervals of time as the planet travels along its orbit. This means that for planets and comets the closer you get to the sun the faster you move and vice versa. For comets with highly eliptical orbits this effect is very pronounced.

Last but not least don't underestimate how powerful the sun's gravity is. Imagine how many rockets it would take to fly Jupiter, a planet so big it has storms that could swallow this planet whole, around in a big circle. The sun's gravity is powerful enough to do exactly that even though they are half a billion miles apart. --LiamE 13:36, 20 August 2007 (UTC)

Orbital periods

I notice that the orbital periods of some comets are specified in years and others in 'a' (Julian years). This is OK, I guess, despite prefering years, but some pages do not have a hyperlink explaining what 'a' is (e.g. 14P/Wolf). I attempted to edit one but the required text did not appear for some reason. Maybe someone could look into this? Regards - a passerby. —Preceding unsigned comment added by 20.133.0.14 (talk) 15:54, 25 October 2007 (UTC)

Question

Do we have a list of comets wich will be seen in the near future? —Preceding unsigned comment added by 88.195.103.107 (talk) 20:33, 7 December 2007 (UTC)

Confusion/contradiction

The article says that in comet nomenclature "C/" indicates a non-periodic comet, and yet the articles for some of them (e.g. Comet Bennett, C/1948 V1, Comet Hyakutake are the ones I looked at) state an orbital period. If something is non-periodic then it can't have an orbital period, can it? I made a similar comment at Talk:List of non-periodic comets. It would be great if someone who understands this stuff could fix these definitions so that they can be understood by the ordinary reader. Matt 13:45, 25 December 2007 (UTC).

Hi. I'm not sure about this either, but you are probably more likely to find an answer at the science ref desk than here, because that page is looked at more often. It would also probably be a good idea to tell them that you posted talkpage comments here, so that they may be able to discuss with you here sooner. Remember, though, that a detailed clarification will require the use of reliable sources. Hmm, my guess would be that people decided that nobody would be able to live long enough to see one of these "non-periodic" comets twice? Well, you could also try searching on the Internet for this. However, if there are many conflicting definitions to be found (don't use wiki-based websites, including sister projects or Wikipedia mirrors or forks as your source), you will probably have to discuss more. Thanks. ~AH1^(TCU) 18:24, 26 December 2007 (UTC)

I tried to clarify the concept of periodic as defined in the given reference at [4]. HTH. Awolf002 (talk) 19:03, 26 December 2007 (UTC)

Right, thanks, I see you've amended it to read: "C/ indicating a non-periodic comet (hyperbolic orbit or orbital period larger than 200 years)". I guess this is OK, but the problem remains, as far as I see it, that it reads like a direct contradiction. It's exactly the same problem as at List of non-periodic comets: it simply looks as if someone's made a slip and got their terms muddled up. It also directly contradicts the definition given earlier in this article under "Orbital characteristics". I wonder if we should, in Wikipedia, avoid altogether the use of the terms "periodic" and "non-periodic" when we actually mean "short-period" and "long-period or non-periodic" respectively. If we must use the terms "periodic" and "non-periodic" in this sense, because it's such a well-established convention, then I think we should add a note saying that the terms are misnomers (I'm assuming they are), used for historical reasons, blah blah, whatever. I'm not quite confident enough that I know what I'm talking about to make this change across all the affected articles though. Maybe if no-one objects in a while I'll go ahead and do it. Matt 02:49, 27 December 2007 (UTC). —Preceding unsigned comment added by 86.136.194.71 (talk)

OK, I just found a reference at http://www.nightskyhunter.com/An%20Observing%20Guide%20To%20Comets.html, which says:

"'C' stands for a long period comet (a comet with an orbital period greater than 200 years) and 'P' stands for a short period comet (orbital period less than 200 years)"

I think this is the sort of thing we should be saying -- It's so much less confusing. (Though presumably we should also mention that "C" is used for non-periodic comets on hyperbolic/parabolic oribts). Matt 03:03, 27 December 2007 (UTC).

OK, I've done a few things. I tweaked the explanation of "periodic" and "non-periodic" under "Orbital characteristics". If you're sure that "periodic = period < 200 years" and "non-periodic = single-apparition or period > 200 years" are the official definitions then maybe you could add that in. I also tweaked the parenthetical definitions under "nomenclature" to try to make it clearer to the reader that yes, these really are the definitions used here, and no, it's not a mistake. I also added an additional clause "or confirmed observations at more than one perihelion passage" which is present in the reference, and took the opportunity to put into more readable bullet point format. Matt 18:41, 28 December 2007 (UTC). —Preceding unsigned comment added by 86.142.111.76 (talk)

Recent Stardust results

Added the following to the end of the "controversy debate over comet composition" section. Assume it should be non-controversial based upon reliable sources cited (news sites [BBC News, Physorg.com, space.com & Wired News] & Lawrence Livermore National Laboratory):

• However, more recent data from the Stardust mission show that materials retrieved from the tail of comet Wild 2 were crystalline and could only have been "born in fire." More recent still, the materials retrieved demonstrate that the "comet dust resembles asteroid materials." These new results have forced a rethink about the very nature of comets and their distinction from asteroids.

Thx, Mgmirkin (talk) 00:38, 29 January 2008 (UTC)

Protect Page

Is it time to protect this page? -- Kheider (talk) 15:36, 10 April 2008 (UTC)

Harbingers of Good and Evil

Shakespeare wrote: "When beggars die there are no comets to be seen. But the sky blazes forth the death of princes." So I propose a subsection be added Role of Comets in Human Culture. Pomona17 (talk) 17:02, 27 May 2008 (UTC)

Currently visible comets

I've removed the section on currently visible comets because it is long out of date. This section should only be included if someone is willing to maintain it. There are websites such as http://www.aerith.net/comet/weekly/current.html where this information can be found. --mikeu ^talk 19:44, 24 October 2008 (UTC)

comets are very long and dull and boring —Preceding unsigned comment added by 74.170.165.82 (talk) 03:47, 12 February 2009 (UTC)

Galileo Galilei and the comets

It appears to me that Galileo exposed his vision about comets in the book "Il Saggiatore".
[5]
[6]
[7]
Drake & O'Malley, The Controversy of the Comets of 1618
[8]

--Cesarakg (talk) 18:25, 31 May 2009 (UTC)

Add a section on calculation of comet orbits?

Discuss method(s), historical background of orbit determination, maybe some math, but not overwhelming. Discuss uncertainties, especially since eccentricities can be so close to unity. Or should this be a separate article? Forgive me if this is already on Wikipedia, but I didn't find it (if it is already here, add to See Also...). Rb88guy (talk) 01:16, 27 August 2009 (UTC)

Ok, I just found an article Orbit determination but frankly it doesn't say much and has no references. Since this is a pretty big subject probably the best approach would be to fix that article up and then refer to it here. Rb88guy (talk) 02:05, 27 August 2009 (UTC)

Correcting a several mistake

First, sorry for my bad English. The definition has a serious error. It is really correct to call it small solar system body, according to the redefinitions of the IAU on August 22, 2006, but the definition is wrong: "A comet is a Small Solar System Body that orbits the Sun," first is redundant, since all Small Solar System Body orbits the sun (except satellites) and this definition brings meteoroids, asteroids, comets and space dust even . The correct definition of these concepts should be separate and should be: "A comet is a Small Solar System Body that has coma and is bigger than a meteoroid". Being larger than a meteoroid it is distinguished from them, and having coma it is distinguished from asteroids. Small Solar System Body distinguishes comet from planet and dwarf planet. —Preceding unsigned comment added by 89.128.219.87 (talk) 00:22, 20 October 2009 (UTC)

Query

The article says:

In the outer solar system, comets remain frozen and are extremely difficult or impossible to detect from Earth due to their small size. Statistical detections of inactive comet nuclei in the Kuiper belt have been reported from the Hubble Space Telescope observations,[15][16] but these detections have been questioned,[17][18] and have not yet been independently confirmed.

As I understand it, numerous TNOs have been observed with certainty. How is it known that none of these are potential comets? Conversely, why is it thought these tenuous Hubble observations are comet nuclei? What is the distinction? Is it one of size perhaps? Or something else? 86.134.30.206 (talk) 03:34, 11 November 2009 (UTC).

Tar?

There's a sentence claiming that their low albedo (lower than asphalt) is actually due to tar-like compounds on the surface. This seems ridiculous to me, though IANAA. Any experts care to comment on either/both statements? (the low albedo, and its cause) —Preceding unsigned comment added by 199.172.169.36 (talk) 12:34, 16 November 2009 (UTC)

Error in the retrieved date of reference 7

" "How Many Comets Are There?". Rosetta FAQ. European Space Agency. 9 November 2007. Retrieved 2000-04-25."

Retrieved 2008 or 2009 more likely. --130.228.251.10 (talk) 07:42, 16 December 2009 (UTC)

Resolved

 – Accessdate updated after ensuring the ESA cite still mentions "trillion". The error looked like a simple miss-key as it was made on 2009-04-25 and 0 is next to 9 on the keyboard. Thanks for the heads-up. --84user (talk) 09:36, 16 December 2009 (UTC)

Hill sphere dimensions - very outdated

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 McWalter ☻ Talk 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

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)

I agree with this. Akuma809 (talk) 01:30, 8 March 2017 (UTC)

Contradiction tag

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

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

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

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

• McNaught 2006 mag -4
• Comet Hale–Bopp 1997 mag 0
• Comet Hyakutake 1996 mag 0
• Comet Holmes 2007 mag 2.5
• Comet Lulin 2009 mag 5

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?

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

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

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 < T_Jupiter< 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 (T_Jupiter > 3; a < a_Jupiter), and Chiron-type comets as (T_Jupiter > 3; a > a_Jupiter). -- 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'

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

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 (talk • contribs) 15:13, 5 April 2013 (UTC)

Dirty Snowball

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)

We can discount the "dirty snowball" theory and the entire claimed formation of comets. Dolomite and other minerals requiring liquid water have been found in comet dust. Liquid water is not found in the vacuum of space - but requires a planet with an atmosphere in the habital zone of the sun to form. I think it's time we revised our outdated beliefs about what comets are and how they were formed.Steven J White (talk) 21:09, 12 May 2015 (UTC)

We still have so little data that we shouldn't make assumptions one way or another. Further, Wikipedia is not the place to advance new theories. — Huntster (t @ c) 23:11, 12 May 2015 (UTC)

The Stardust Mission captured samples of comet dust from Wild 2. The analysis of the materials gathered there struck a blow to falsify the dirty snowball and oort cloud formation theory, as Steven J White indicates. Donald Brownlee, the principal investigator in the Stardust Mission, said "The comet samples collected by Stardust contain abundant crystalline minerals and in most cases it is clear that they did not form by the predicted mild heating of interstellar dust." Furthermore, water-ice was presumed to be a large part of a comet's composition, but the amount of water found on the nucleus samples of Wild 2 were trivial. What this combined with the presence of dolomite, certain sulfide minerals, and iron, that can only be formed in the presence of liquid water, not frozen. Olivine is also present in the sample, which would break down in the presence of water. The silicate mineral forsterite was also present, which requires extreme heat to form. As NASA curator Michael Zolensky says, "That's a big surprise. People thought comets would just be cold stuff that formed out... where things are very cold." Brownlee also said "When these minerals formed they were either red hot or white hot grains, and yet they were collected in a comet, the Siberia of the Solar System." There were samples of cubanite, phyrrhorite, and only trivial levels of cosmic dust. These indicate many diverse conditions and temperatures of formation, and the traditional explanation of comet formation is inadequate. Either compositional zoning or the oort cloud theories are falsified. Deep Space 1's flyby of the comet Borrelly puts another nail in the coffin: the probe could find no traces of water at all. Laurence Soderblom of the U.S. Geological Survey said "The spectrum suggest that the surface is hot and dry. It is surprising that we saw no traces of water ice." More confirmation: the fragments of Shoemaker-Levy 9 were again devoid of volatile gases from sublimated ices. Same thing in comet Elenin, a complete lack of water. Nowhere is water found in any significant measure on cometary nuclei. There's a wealth of data one way, Huntster. The moniker "icy" or "snowy" anything is misleading. Disclaimer, claim of fair use: "Symbols of an Alien Sky: The Electric Comet" is where I got this information, but I have a feeling that cross referencing these findings would not be difficult. But, I'm not a proficient wiki editor, I just hope someone will come along and see the truth through! :D 65.182.164.240 (talk) 17:16, 19 April 2016 (UTC)

Right now we have more questions than answers, and until we're able to conduct a vastly more wide-ranging survey of cometary composition throughout the solar system and across a range of cometary ages and conditions, we cannot draw assumptions. You point out examples where there is a distinct lack of detected water/ice, yet 67P/Churyumov-Gerasimenko is actively releasing water vapour, and Philae found evidence of hard ice beneath a layer of dust. Additionally, molecular oxygen and nitrogen found there suggests a formation in a low-temperature environment. So, yeah, not enough information yet. — Huntster (t @ c) 03:27, 20 April 2016 (UTC)

To the contrary, Philae found a pocket (a small pocket, the reported water content is only about 4.6% of the area analyzed) of hard ice on an inactive portion of the comet. The unspoken assumption is that there are large amounts of water-ice below the surface, in the nucleus. This assumption is unwarranted. We have plenty of answers, methinks, and plenty of alternate explanations for the presence of diverse materials on comets, including water and its vapor, particularly those enjoined by the electric universe theory. (Here, I'd like to encourage readers to check out the Thunderbolts Project and the aforementioned episode of Symbols of an Alien Sky. They're wonderful, elegant explanations of how the universe operates. On comets, they explain the presence of water and hydroxyl in the coma, and its relative absence in the nucleus well.) They're just not the explanations some would like to hear. Regardless, the information you presented is, in this editor's humble opinion, nowhere near enough to hold back the tide of evidence that comets in general are not icy or dusty, but rather that they are rocky and dry, but more importantly complex and diverse. The moniker is still unwarranted, even granting insufficient data to either side, so we must still remove the label. 65.182.164.240 (talk) 16:42, 20 April 2016 (UTC)

Call a comet an "icy dirtball" if that term makes you feel better. But any 2 word term is not going to be a quality definition for what a comet is. Any other claim will require a reliable source. -- Kheider (talk) 18:23, 29 October 2015 (UTC)

Proposal

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. James^x12345 21:50, 20 August 2013 (UTC)

GA Review

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

Rate	Attribute	Review Comment
1. Well-written:
	1a. the prose is clear, concise, and understandable to an appropriately broad audience; 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. reliable sources are cited inline. All content that could reasonably be challenged, except for plot summaries and that which summarizes cited content elsewhere in the article, must be cited no later than the end of the paragraph (or line if the content is not in prose).	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 editorial 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 media such as images, video, or audio:
	6a. media are tagged with their copyright statuses, and valid non-free use rationales are provided for non-free content.	All from Commons.
	6b. media 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

• 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. James^x12345 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

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. James^x12345 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. Serendi^podous 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

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

However, BBC reports in 2013:

"...The Sun's intense gravitational field produces tidal forces that will also have a major effect on the comet."[9]

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)

Number of comets in "reservoir"

The statement that "the reservoir of comet-like bodies in the outer Solar System may number one trillion" was deleted as being "absurd" (here), but I suspect it may noy be absurd at all.

We don't know how many comets there are since most have never been seen. There could be one hundred billion in the Oort cloud. (https://solarsystem.nasa.gov/faq/index.cfm?Category=Comets)

The Oort Cloud probably contains 0.1 to 2 trillion icy bodies in solar orbit. Occasionally, giant molecular clouds, stars passing nearby, or tidal interactions with the Milky Way's disc disturb the orbits of some of these bodies in the outer region of the Oort Cloud, causing the object to fall into the inner solar system as a so-called long-period comet. (https://solarsystem.nasa.gov/planets/profile.cfm?Object=KBOs&Display=OverviewLong)

This has come to be known as the Oort Cloud. The statistics imply that it may contain as many as a trillion (1e12) comets. (http://nineplanets.org/kboc.html)

As I cannot claim to be an expert personally on this I am not going to restore it. However, restoring some indication of the (most probably) truly vast number of these bodies should be considered. 109.156.50.215 (talk) 01:16, 22 January 2015 (UTC)

---

I removed that information in the past mainly because the citation was totally unrelated. Now that you provided a solid reference, I guess it's ok to add the information back in the article. I still think a trillion comets is way too much, though. Tetra quark ^{(don't be shy)} 01:37, 22 January 2015 (UTC) -- blocked user sockpuppet

In the first lead paragraph, and in the interior section on characteristics, it is stated that comet nuclei range in size from a few hundred meters on up. Sagan and Druyan 1997 are cited. This seems interesting. What happened to smaller comets? I would have thought that the size distribution of comet nuclei would follow something like a power law, in which case comets of small size would be relatively common, at least out in the Oort Cloud, though small comets might evaporate upon close passage with the Sun. A power-law distribution would mean a total comet population that is effectively infinite (in terms of this model, of course). Isambard Kingdom (talk) 12:23, 24 January 2015 (UTC)

A trillion (10¹²) comets seems like a reasonable number as comets are the leftover building blocks of the solar system and the Oort cloud is up to ~200,000AU across as it blends into the interstellar medium in all directions. At the edge of the Oort cloud numerous objects will be moving in and out based on external perturbations over the last million years or so. -- Kheider (talk) 16:17, 24 January 2015 (UTC)

@Kheider, any knowledge on the number vs size distribution of the Oort cloud objects? Isambard Kingdom (talk) 17:55, 24 January 2015 (UTC)

Hi there, @Tetra quark, you removed the above mentioned citation because the part that contains the statement about the trillion comets is not visible unless you click on the "continue" button on ESA's website. I think it was just a misunderstanding. I suggest to reinsert the removed citation and to use an additional Template:Cite_web#Quote-attribute to be more explicit as I almost failed to notice the hidden part of the ESA-article as well. Cheers, -- Rfassbind -talk 23:35, 24 January 2015 (UTC)

Rfassbind, I've already readded the material, using two books as citations. No need for further work. — Huntster (t @ c) 23:44, 24 January 2015 (UTC)

Very well. Hope my explanation of what might have been the cause for the misunderstanding was nonetheless helpful for everybody involved. Cheers, -- Rfassbind -talk 01:12, 25 January 2015 (UTC)

Yes, I strongly expect that your supposition is spot on for what happened. — Huntster (t @ c) 05:29, 25 January 2015 (UTC)

Oxygen discovery

Rosetta has found molecular oxygen on comet 67P and that's important and has amazed the scientists. This evidence of oxygen as an ancient substance will likely discredit some theoretical models of the formation of our Solar System, the scientist emphasized. Read more on the website below:

Read more at: http://phys.org/news/2015-10-rosetta-molecular-oxygen-comet-67p.html#jCp http://phys.org/news/2015-10-rosetta-molecular-oxygen-comet-67p.html

MansourJE (talk) 21.36, 29 October 2015 (UTC)

MansourJE (talk) 03:03, 16 December 2015 (UTC)

Oxygen as Common Element

As explained before oxygen has been found on comet 67P, the new study also found it on comet 1P Halley. It shows that molecular oxygen might be present on other comets. So this question rise up, is oxygen the only essential element for life on the galaxy. Read more on

http://phys.org/news/2015-12-molecular-oxygen-common-comets.html

MansourJE (talk) 06.34, 16 December 2015 (UTC)

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Maximum size

"Comet nuclei with radii of up to 30 kilometers (19 mi) have been observed..."

But Hale–Bopp was 60 km. --Mortense (talk) 00:54, 9 July 2020 (UTC)

Radius is 1/2 diameter so 30*2=60. -- Kheider (talk) 02:37, 14 November 2020 (UTC)

definition

Doesn't really cover comets outside of our star system - as comets must be extremely common throughout the universe . . . 50.111.24.158 (talk) 02:31, 14 November 2020 (UTC) see --> https://www.npr.org/2019/12/05/784898213/a-comet-from-another-star-hints-that-our-solar-system-isnt-one-of-a-kind and --> https://www.nationalgeographic.com/science/2019/09/bizarre-interstellar-comet-from-another-star-system-just-spotted/

the Mayan culture and comets

see --> https://www.tandfonline.com/doi/abs/10.1080/10556790108221607 ... something about the Maya, and the Babylonians/Sumerians (the Sumerian_K8538 tablet), for that matter, should be added to the section of the article.50.111.24.158 (talk) 15:06, 14 November 2020 (UTC)

Comet is not ice

Please keep the wiki updated with latest evidence that comets is NOT icy loose collections of particles. — Preceding unsigned comment added by Einar Bordewich (talk • contribs) 17:39, 8 October 2021 (UTC)

Comets are icy dirtballs. Calling them dirty snowballs was not the best description. Ices refer to volatiles.-- Kheider (talk) 18:01, 8 October 2021 (UTC)