Talk:Comet/Archive 1

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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


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)


"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)


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)


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.

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 (talkcontribs) 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. Markyour 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. Markyour 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: ☄ (&#x2604;). 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?--Viridistalk|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." [1] [2] More recent still, the materials retrieved demonstrate that the "comet dust resembles asteroid materials." [3] [4] [5] These new results have forced a rethink about the very nature of comets and their distinction from asteroids. [6]

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)


Cite error: There are <ref> tags on this page, but the references will not show without a {{reflist}} template (see the help page).