Talk:3753 Cruithne

Not a moon!

I see that AStudent has recently changed this page so as to remove the "incorrectly" from "... sometimes incorrectly described as Earths second moon". Folks, I know it would be romantic to have another moon, but Cruithne is simply not a moon of the earth! It isn't even remotely close to being a moon of the earth! Any suggestions as to how we can put that idea into the article in such a way that the romantics won't remove it? Chrisobyrne 12:43, 18 October 2006 (UTC)

Saying it is "sometimes described as Earth's second moon" is true. Saying it is Earth's second moon would be different, and wrong. Inserting little disqualifiers like 'inaccurately' seems a bit prescriptive to me, but I won't remove it myself. I think something better would be a very concise explanation of (i) why it is called Earth's second moon and (ii) the fact that it is not a satellite of the Earth ("moon" has no strict astronomical definition anyway, I think.) Robin Johnson (talk) 11:26, 19 October 2006 (UTC)

I'm concerned that not having a qualifier like "incorrectly" could be interpreted as an endorsement of the "second moon" statement. As to the answer to your first question (why it is called Earth's second moon), I suspect that the answer is "because it's a romantic notion". The scientists words are being mis-interpreted by people who want to hear that we have another moon. Frankly, I don't think this article is a place for that discussion - I think that's a discussion that belongs on a human psychology page somewhere. Chrisobyrne 10:15, 20 October 2006 (UTC)

I disagree with "moon has no strict astronomical definition". According to Wikipedia :) "moon" means the same thing as "natural satellite". And, as an astronomer, that is also my understanding. And, I think the definition of "moon" would have to be stretched beyond breaking point before it could possibly include Cruithne. Chrisobyrne 10:23, 20 October 2006 (UTC)

Sorry for bringing this up again, but... It's not Earth's second moon, and scientists do not refer to it as such. I think that we are doing a disservice by saying that "some refer to it as Earth's second moon", because the only people who do so are popular science writers, and they (almost?) aways say that it is not. Even the reference cited in this topic is somewhat vague as to whether it should be called a moon or not. In short, I think "Earth's second moon" should be relegated to bad journalism. Personally, I liked the old intro that mentioned it was inaccurate to call it a moon. Lunokhod 00:03, 28 February 2007 (UTC)

Yes, but that's what's now written in the article, isn't it? Chruithne is just nicknamed "Earth's Second Moon"; I guess no scientist would ever consider this a valuable scientific statement. But I think, this fact is at least worth mentioning. — N-true 14:15, 28 February 2007 (UTC)

It would be handy if someone could provide evidence in either direction, because as I heard it it might be a moon of the Earth, but there is a split in the astronomical community, much like that over the classification of the term "planet". If anyone has any evidence rather than saying "No scientists say it is one so get over it" to paraphrase, then this debate gets nowhere, and ultimately neither side has any validity to their statements. I could say no scientists believe that monkeys exist but that doesnt consitute evidence to the suggestion that they dont exist, nor to the statement that no scientists think they do.

Indeed, while this is an article from 8 years ago, and may well be out of date, it does suggest that at one time scientists WERE calling it a second moon. http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=11640

Indeed, here is a much more recent article (2005) that states it IS a "sort of" moon. http://www.rigel.org.uk/newsletter/200512/ EdB 101 02:15, 13 April 2007 (UTC)

A "moon" is both scientifically and colloquially accepted as meaning an object that orbits a planet. This fact is plainly obvious, and looking up any remotely reputable definition for the term "moon" will make this abundantly clear. It is not necessary to provide evidence of scientists calling it a moon or not. If a scientist did s/he was in error, or was not speaking literally. Because Cruithne does not orbit Earth it is misleading to refer to it as a moon. It orbits the sun! I fully agree that the original text: "sometimes incorrectly described as Earths second moon" is accurate and provides the best explanation of the facts. I realize this is now a rather old discussion, but obviously it needs to be reexamined. TragiCore (talk) 19:48, 3 March 2009 (UTC)

2011 revisit

I have no axe to grind, but I find this discussion unsatisfactory. It seems obvious to me that the fact that an object orbits the sun is no argument against it also orbiting the earth; our existing Moon does both, as I think everyone will agree. Further, I am not at all certain that I know what criteria should be used to decide whether 'A orbits B' is a true statement. No-one has attempted to define this, and therefore to provide a reason for asserting one way or another whether Cruithne orbits Earth. Looking at the first animation (which I know is a 2-dimensional representation of a 3-D reality; the plane of Cruithne's orbit around the sun is inclined to that of the earth), it seems to me that the displacement vector from the Earth to Cruithne rotates monotonically through 360 deg during each period of the motion of the objects. Could this be used as a definition of 'A orbits B' (perhaps with the added condition that the vector should remain in a plane)? This definition would lead to the conclusion that the Sun orbits the earth, which might be an objection, but this could be overcome by acknowledging that 'A orbits B' is not in fact a scientific statement or concept. In reality both objects orbit a common centre of mass. So what I have proposed is actually a putative definition of 'mutual orbital motion' or some such concept. Can someone who knows something about this topic in depth please clear this up in a rigorous way ? — Preceding unsigned comment added by 82.32.48.177 (talk) 09:21, 11 November 2011 (UTC)

I do not think Cruithne every comes close enough to the Earth to even become a temporary satellite capture. I could claim that the Earth orbits the space station, but you already know that is a ridiculous statement "for general use", even if mathematically true. -- Kheider (talk) 12:52, 11 November 2011 (UTC)

Hey Kheider - thanks for your comment. What I am asking for is a formal definition of the meaning of 'A orbits B' so that we can answer the question 'Does Cruithne (C) orbit Earth (E)?' and give a reason for our answer. I have proposed a possible definition; if it is accepted then I would say that the first animation on the main page suggests that 'C orbits E' is a true statement. There might be an alternative definition which makes that statement false, but I would like to know what it is. How do you describe the kind of motion which makes the statement 'a space station orbits the earth' true ? Are you using the definition I have given, for example, or if not, what definition are you using ? Would you be happy with my definition if we include a requirement that the common center of mass is inside E (or B in the general case)? If we add this requirement we would not be able to say that the components of a double star orbit each other, and that might be unsatisfactory. (Dr Andrew Smith) — Preceding unsigned comment added by 82.32.48.177 (talk) 18:06, 13 November 2011 (UTC)

The first animation shows a 1:1 Orbital resonance and has nothing to do with Cruithne orbiting the Earth. Pluto does not orbit Neptune even though they are in a 2:3 resonance. -- Kheider (talk) 18:26, 13 November 2011 (UTC)

OK I see I will not get an answer to this. You continue to use terms without defining them. -- (Andrew) — Preceding unsigned comment added by 82.32.48.177 (talk) 22:25, 13 November 2011 (UTC)

Let me put this another way: When was the last time your saw Earth's moon on the other side of the Sun? When was the last time you saw the Earth's moon beyond Mars? A moon is suppose to orbit the primary body faster than it "orbits" any secondary body. -- Kheider (talk) 23:09, 13 November 2011 (UTC)

Right - now you are beginning to bite on the question. You are have added a condition to my initial definition (I suppose); namely your final sentence. However if we understanc 'faster' as meaning 'with a shorter period', then it appears that C's motion is a limiting case of allowed moons since it orbits E & S with equal periods (I think - based on the animation). I was about to ask "suppose the Moon's orbit were to increase; would there be a point at which 'M orbits E' would become untrue ?". You seem to have answered this. My second question is "Is the trajectory of C consistent with the situation which would exist if the period of a satellite of the earth were to be increased until it becomes equal to a year ?" If the answer to this is 'yes' then I would say that this is justification for saying that C is 'like' a second moon, but with an orbital period that is at the extreme limit of acceptable values for it to be said to be a moon. Andrew. — Preceding unsigned comment added by 82.32.48.177 (talk) 09:56, 14 November 2011 (UTC)

From the orbit article: "An orbit is the gravitationally curved path of an object around a point in space". As can be clearly seen in the pictures in the article the point in space Cruithne's orbit is curved around is the Sun/SS Barycenter, not Earth/Earth–Moon barycenter. Hence Cruithne is not a moon. --JorisvS (talk) 11:18, 14 November 2011 (UTC)

Hi JorisvS - Thanks for your contribution. You might accuse me of logic-chopping, but E does in fact occupy a point (or more than one point) in space around which C's path curves. That is the point I made in my original posting. There are many such points within the loop of C's trajectory. You will have to find a better definition than this in order to reach your conclusion. I'm afraid you have committed a non-sequitur; the correct logical conclusion is exactly the opposite of the one you reach. A

A question

A question: this page states that the next time 3753 Cruithne will be gravitationally sling-shot by earth and have a series of close approaches will be around 2292 - but the page for 2285 writes that this will occur in 2285. Could someone clarify this?

"Cruithne shares Earth's orbit, but does not actually orbit the Earth. Instead, it follows a spiralling path that moves along the Earth's orbit in a horseshoe shape, the two ends of the horseshoe approaching either side of Earth but not quite reaching it. It takes Cruithne 385 years to complete one such horseshoe orbit."

- Not to sound stupid but I am not following this dicussion of Cruithne's orbit. Huh?  :-) (I think we need to specify: horseshoe-shaped as observed from where?)

Take a look at the diagrams and animation of Cruithne's orbit in the external link provided at the bottom of the page. If you can come up with a simple textual description of that, you are most welcome to replace the one above. :) -BD (Actually, since the images on the page are © Paul Wiegert, I'll email him and see if I can get permission to use them in Wikipedia. I don't think that a simple textual description is possible, period. :)

Good God! If I'm understanding that right, it IS horseshoe-shaped!!

Well, only from the perspective of the Earth. From the perspective of an observer who isn't viewing the situation from a point orbiting the sun at Earth's orbital radius, Cruithne is actually following a relatively conventional elliptical orbit around the sun. But since that elliptical orbit has almost exactly the same period as Earth's, it behaves as if it's orbiting around the Earth in this weird manner. I've just emailed Dr. Weigert for permission to use some of his diagrams here, when I get a response I'll see about trying to explain this more clearly. It's cool. :) -BD

"a relatively conventional elliptical orbit", Okay, thanks, that restores my faith in God and Newton.  :-)

Not forgetting Kepler, if you please! - Lee M 01:28, 4 Sep 2003 (UTC)

"But since that elliptical orbit has almost exactly the same period as Earth's, it behaves as if it's orbiting around the Earth in this weird manner."

NO IT DOESN'T! Have another look at the animation - even if you hold the Earth still, Cruithne KEEPS TO ONE SIDE of the Earth - it does not orbit AROUND the Earth. The horseshoe slowly migrates until it's edge comes close to the Earth, whereupon it reverses direction so that the effect can repeat itself with the other edge of the horseshoe after another 385 years (orbital inclination notwithstanding). There is a myth out there the Cruithne is a moon of the Earth, and I think everything possible needs to be done to kill this myth. (I know that Paul Wiegert says "The near-Earth asteroid 3753 Cruithne is in an unusual orbit about that of the Earth" - I think his choice of the word "about" is unfortunate, I think he probably means "in relation to").

No, he means "an unusual orbit about the orbit of the Earth". HTH HAND --Phil | Talk 14:58, Dec 23, 2004 (UTC)

Temperatures

The article gives the average surface temperature of Cruithne as 378 Kelvin, that's well above the boiling point of water. How can that be for an object orbiting the sun at an average distance comparable to earths distance and without an atmosphere for any greenhouse effects? Does anyone have an explanation for this? 84.160.196.181 14:23, 27 Feb 2005 (UTC)

The low albedo is responsible. The temperature estimate is computed from the albedo and assumes the surface reaches thermal equilibrium over multiple rotations, using the semi-major axis distance.

Urhixidur 18:47, 2005 Feb 27 (UTC)

A good discussion of the physics involved is, for example, Marco Delbo's The nature of near-earth asteroids from the study of their thermal infrared emission Chapter 2: Sizes and albedos of asteroids: the radiometric method and asteroid thermal models.

Urhixidur 22:20, 2005 Feb 27 (UTC)

Thanks for the explaination. I'm not quite satisfied because when looking at the moon its albedo (0.12) is even slightly lower than Cruithnes but the everage temperature is much colder. Hm, when realylooking at the moon it is quite bright so the albedo of 0,12 seems wrong. 84.160.223.61 15:05, 5 Mar 2005 (UTC)

The calculation goes like this. Assume thermal equilibrium, which means there is as much energy being absorbed per unit of time (from the Sun's rays) as is being emitted. The energy flux absorbed is a fraction of the solar luminosity (L_o = 3.827×10²⁶ W) determined by the ratio of the asteroid's presented surface (πd²/4, where d is the asteroid's diametre) to the orbital sphere (4πR², where R is the orbital radius). The albedo intervenes at this point; the energy flux absorbed is the fraction (1-A). Obviously, an albedo of 1 (perfect reflector) means no energy flux is absorbed. The energy emitted is the asteroid's surface (πd²) times the all-wavelength energy flux per unit surface, given by (σT⁴), where σ is the Stefan-Boltzmann constant (5.670 399 102 108 67×10^-8 W/m²K⁴). This is true for a black body (perfect radiator); for asteroids, an emissivity ε of 0.9 is assumed. Thus we have:

$\sigma T^{4}\pi d^{2}\epsilon ={\frac {(1-A)L_{o}d^{2}}{16R^{2}}}$

hence

$T^{4}={\frac {(1-A)L_{o}}{16\pi R^{2}\sigma \epsilon }}$

For the Earth, this calculation yields an average temperature of 255 K (actual average: 287 K); for the Moon, it yields 277 K (vs 250 K). This gives an idea of the error inherent in these estimates.

By the way, thanks for having me take a look at these again; it allowed me to spot a mistake that has resulted in systematically too high estimated temperatures in the asteroid articles!

Urhixidur 15:53, 2005 Mar 5 (UTC)

Thanks again. Now I have a better understanding. The T⁴ causes the average temperature to fall when maximum and minimum temperatures differ more strongly. Thus heat transport on the asteroid as well as the rotation period might have a significant impact.

By the way, when in some decades the first human will set foot on Cruithne I will proudly be telling my grandchildren that it was me that gave the crucial hint on not going too lightly clothed and better be wearing a double pair of woolen socks ;-) 84.160.223.61 19:11, 5 Mar 2005 (UTC)

Note that in the case of a strongly eccentric orbit, the definition of "average" temperateure used here is wrong --we're using the semi-major axis, whereas the time-averaged orbital radius is actually a(1+e²/2) (see here). Considering the asteroid's actual thermal regime (i.e., thermal inertia) complicates the calculation even further.

Urhixidur 01:44, 2005 Mar 6 (UTC)

Pronunciation

Paul Wiegert's page about Cruithne gives a different pronunciation than that given here. He says it has just two syllables, with the stress on the first. Who's right? --agr 05:17, 20 Jun 2005 (UTC)

Wiegert is right. The word is definitely two-syllabled with the stress on the first syllable. Krü-nyeh is a pretty good approximation of the correct Gaelic pronunciation. I guess KREEN-yeh would be the easiest way for Anglophones to pronounce it. That's my two cents, anyway! Eroica 12:48, 13 August 2006 (UTC)

Hi! If that is the truth, please correct this article with IPA. But, I wonder "Correct Gaelic pronunciation will be the two-syllabled one, but as an English word, how astronomers pronounciate it?"

In ja.wikipedia, a discussion about pronounciation of this asteroid is going on. Because foreign names are spelled in Japanese according to its pronounciation.--NJT 09:29, 24 August 2006 (UTC)

Is there an acute accent in the Irish spelling? If not, there's no /u/ sound, as in duine /ˈd̪ˠɪnʲə/ "person", and the nearest English would be /ˈkrɪn.yə/. If there is, as in súil /suːlʲ/ "eye", then there's no /i/ sound, and the nearest English would be /ˈkru.nyə/ (at least according to Wikipedia). Based on the cited sources, it might be the latter. I'm going to go ahead and put that in, on the rational that I might be right and the current listed pronunciation isn't even English, so correct me if I'm wrong. As pointed out above, what we really need is how astronomers pronounce it, but I imagine they're as clueless as we are, and each likely has his own idiosyncratic pronunciation. kwami 22:24, 8 May 2007 (UTC)

It would be great if you did not change the pronunciation of the Irish when I correct it AGAIN. -- Evertype·✆ 22:41, 9 May 2007 (UTC)

(And sorry, it wasn't you. My mistake.) -- Evertype·✆ 22:42, 9 May 2007 (UTC)

Cruithne would also be pronounced /krihənə/ with a palatalised n. That's how I would say as a Munsterman although other Irish dialects would be less inclined to pronounced the intervocalic /h/. I believe the Scots would probably say /krunjə/ but I can't be sure. I don't know how the Manx would pronounce it. I expect English speakers will use their own (incorrect) pronunciation anyway, as seen in ogham and crannóg. An Muimhneach Machnamhach (talk) 22:15, 8 June 2008 (UTC)

Quibble: "jə". Then you link to this "http://en.wikipedia.org/wiki/Wikipedia:IPA_for_English" page for pronunciation guide. Find me that symbol on that page, please... A guide which isn't one isn't a guide. "How do I get from Miami, Florida, USA, to New York City, New York, USA?" "Well, you head south for a bit, then east." :-/ 24.250.195.181 (talk) 22:05, 11 January 2009 (UTC)OBloodyHell

"Croothny" would seem to be an intuitive English pronunciation. Rothorpe (talk) 23:39, 13 November 2011 (UTC)

Origin of Cruithne's name

"Cruithne was named after the first Celtic racio-tribal group to inhabit the British Isles. The Cruithne (aka Priteni or Picti) emigrated from the European continent and appeared in Britainnia between about 800 and 500 B.C. [1]."

I believe this is incorrect. In Scottish pseudo-history, Cruithne was the name of the first king of the Picts:

Pictish Kings:

"Mythical kings of the Picts are listed in the Lebor Bretnach's account of the origins of the Cruithnians. The list begins with Cruithne son of Cing (see Cruithne), and his sons Fib, Fidach, Foltlaig, Fortrend, Caitt, Ce and Circinn."

It is my understanding that the discoverer of Cruithne, Duncan Waldron, is of Scottish descent. It is also customary to name asteroids after individuals, not racial groupings.

Eroica 12:40, 13 August 2006 (UTC)

You are probably correct, but the main reference source (Schmadel's Dictionary of Minor Planet Names is uncertain whether the tribe or the king was intended. I have qualified the sentence in the article. Thanks for the suggestion. The Singing Badger 18:21, 19 August 2006 (UTC)

YouTube links

This article is one of thousands on Wikipedia that have a link to YouTube in it. Based on the External links policy, most of these should probably be removed. I'm putting this message here, on this talk page, to request the regular editors take a look at the link and make sure it doesn't violate policy. In short: 1. 99% of the time YouTube should not be used as a source. 2. We must not link to material that violates someones copyright. If you are not sure if the link on this article should be removed, feel free to ask me on my talk page and I'll review it personally. Thanks. ---J.S (t|c) 06:58, 7 November 2006 (UTC)

UFO Rumors

This rock has been stated on some websites as being a UFO, and UFO Casebook, Re.:Alien Races state that the reptile aliens are using a asteroid as a ship to get to Earth. 65.163.112.107 06:51, 9 March 2007 (UTC)

Now, how may this be placed ? Several websites do mention that this rock, others are UFOs in disguise awaiting the right time to hit this planet. What would YOU do if you saw a alien battleship/carrier in Earth orbit, yet at one that military assets can't get to it ? 65.163.112.107 06:55, 9 March 2007 (UTC)

Placed "UFO" in article, due to this matter. 65.163.115.203 (talk) 10:27, 17 February 2008 (UTC)

Seen those rumors myself on the indicated website indicated here. Is that shit for real ? If so, I'll eat hot sauce, so that a lizard will get ulcers. 65.163.115.203 (talk) 10:29, 17 February 2008 (UTC)

Are any of these web sites remotely reliable sources?--Bedivere (talk) 22:48, 22 February 2008 (UTC)

The word "UFO" is involked in a pseudo-serious context. Is that an even vaguely serious question? :oP 24.250.195.181 (talk) 22:11, 11 January 2009 (UTC)OBloodyHell

Removing of "misleadingly"...

I had added to the statement of Cruithe being sometimes called a moon the word "misleadingly" (I admit, I had spelled it wrong twice, but I'm no native speaker, sorry). It was twice removed, with the reason that it's a) misspelled, b) a loaded word and c) unnecessary. I agree on a, of course, but not on b and c — I mean, it's clear that 3753 Cruithe is not a moon by definition, but that it's called "Earth's second moon" by various sources. To avoid that people who don't know as much about astronomy take up that term "second moon" or even believe that Cruithe is a moon of Earth, I added the word "misleadingly", to show that the statement is actually not quite correct and even unscientific. This statement should be marked as pseudoscience; maybe someone can find an adverb that's more appropriate? — N-true 18:31, 4 September 2007 (UTC)

Orbiting Lagrangian point L4? Oh no, it's not!

From the Earth-POV animation, it seems the orbit encloses L4. But by the text, this configuration won't last. The orbit will move away from Earth, through L3 and back towards the Earth on the other side, enclosing L5 before moving back away again. Bean-spirally horseshoe shape ...

I guess an animation reflecting this would be too much to ask for, right?  :)

But without any indication in the captions that this configuration is temporary, my first impression was that this asteroid indeed was in a stable orbit around L4. So, could someone please have a look at those captions, so that the very nice animations don't mislead us poor ignorant readers? (I'd make a suggestion, but I'm coming up short.)

Thanks! — the Sidhekin (talk) 20:33, 9 February 2008 (UTC)

Sorry, folks -- I don't believe this is in either the L4 or the L5 positions.

-- 1) L4 and L5 are roughly immobile with regards to the Moon, just located ahead or behind it in the same orbit. You don't "orbit" a lagrange point (mostly) you "sit" in it.
-- 2) L4 and L5 are "semistable" -- stable like a ball at the bottom of a bowl. It is L1, L2, and L3 which only nominally stable (like a ball balanced on an unsecured pin), and those also don't "move" in relation to a line through the centers of the earth and moon. This thing is all over the place. My guess is that it's probably a chaotic attractor. I don't have the time or the immediate skills to evaluate that assumption, though.
-- More here: Lagrangian point —Preceding unsigned comment added by 24.250.195.181 (talk) 23:48, 11 January 2009 (UTC)

Is the section titled "Similar Minor Planets" a typo?

http://en.wikipedia.org/wiki/3753_Cruithne#Similar_minor_planets

I think it should read "Similar NEO's", or something like that. —Preceding unsigned comment added by Chuck starchaser (talk • contribs) 18:08, 11 October 2009 (UTC)

Since this section discusses the moons of Saturn, and the last paragraph is about co-orbital asteroids, I think it is probably better to refer to them as "minor planets" since Jupiter trojans are not NEOs... -- Kheider (talk) 19:18, 12 October 2009 (UTC)

orbit

the article states that the orbit period is less than the earth's, but that isn't a stable relationship ... over a very long period, the orbit is (unless i'm missing something) the same as the earth's. both of these seem to be accurate values for the period (depending on your time frame). shouldn't the article reflect this? when i see a difference i immediately wonder how there can be a 1:1 resonance

All orbits vary due to perturbations. Cruithne has an orbit that is unstable over a long period of time, and on astronomical time scales is only briefly a Quasi-satellite in a 1:1 resonance with the Earth. Basically it is little asteroid that has the same basic orbital period as the Earth. -- Kheider (talk) 15:17, 9 August 2010 (UTC)

Bean-shaped orbit

The animation showing Cruithne's orbit from the perspective of the Earth depicts the Sun as never being between Earth and Cruithne. This contradicts the animation that depicts Cruithne's orbit for real.--Jarhed (talk) 14:55, 16 June 2011 (UTC)

Between 1950 and 2050, Only on 1976-Jan-27 did 3753 Cruithne come within 0.5° of an alignment with the Sun. On 2032-Jan-21 it will be 8.74° from the Sun. -- Kheider (talk) 19:46, 16 June 2011 (UTC)

What contradiction? Both animations show that Cruithne is sometimes further from Earth than the Sun is; neither shows Cruithne passing behind the Sun. —Tamfang (talk) 20:25, 16 June 2011 (UTC)

Sorry, I stand corrected, thanks.--Jarhed (talk) 06:00, 17 June 2011 (UTC)