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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)
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)
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Indeed, while this is an article from 8 years ago, and may well be out of date, it does suggest that at one time scientists WERE calling it a second moon.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)
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)
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)
I'm sorry JorvisvS, there are points which you make which I do not understand, and which seem obviously untrue: (a) the orbit of C is clearly not an ellipse; (b) the path of C does 'curve around the earth' (at least the animation shows that it does); perhaps it would help if you were to be more precise about what you mean by 'is curved around' - I have said how I understand this (see my first posting). But I don't want this to be a sterile argument. I am genuinely interested in knowing why, in conceptually rigorous terms, astronomers want to distinguish between an orbit such as C's and that of M. To say that C's orbit encompasses the sun does not satisfy me: the path of M, considered over a year, also encompasses the sun. It looks to me as though C is simply a case in which the 'month' has become the same as a year (but I might be wrong in this - it is just an impression). This is why I ask - 'what would happen if the orbit of a genuine earth-satellite were to increase ? - Would there be a point at which we would no longer say that it orbits the earth ?' I am sure that the answer to this must be 'yes', but is it possible to define that point or condition precisely ? Perhaps another approach would be to ask, "if the orbit were to increase, would there come a point of instability or discontinuity at which the the nature or the orbit would suddenly change so as to become significantly different from what it was at a smaller radius or shorter period ?. If there is no discontinuity, is the condition 'month=year' an arbitrary point of distinction in the sense that 'month'<year corresponds to 'moon' and 'month'=>year signifies 'non-moon'". -- Andrew — Preceding unsigned comment added by 82.32.48.177 (talk) 14:22, 14 November 2011 (UTC)
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?)
Good God! If I'm understanding that right, it IS horseshoe-shaped!!
"a relatively conventional elliptical orbit", Okay, thanks, that restores my faith in God and Newton. :-)
"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."
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)
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)
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
Someone added a spelling pronunciation with the "th" pronounced, cited to a BBC game show. Actually, the host was corrected at the end, over his earpiece, and said it was "kroo-EE-nyə". That's assuming he repeated it correctly, so it's hardly a RS, but it would be nice to know where the person correcting him got it from. Maybe just sounding it out with the knowledge the "th" is silent but little more?
Here it's /'kru:j.njə/, but again that's an approximation of the Celtic, with a diphthong that does not occur in English. At Forvo we've got an Irish pronunciation of ~ /'krʊnjə/. That would work easily enough in English. — kwami (talk) 00:29, 9 January 2014 (UTC)
"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. ."
I believe this is incorrect. In Scottish pseudo-history, Cruithne was the name of the first king of the Picts:
"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)
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)
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)
UFO's and sentient beings from outer space remain a completely unknown part of the universe. I don't want this in the wiki — Preceding unsigned comment added by 201.241.238.57 (talk) 22:01, 25 August 2016 (UTC)
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)
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)
-- 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)
Cruithne certainly seems to be in a tadpole orbit around Lagrangian point L4, just as much as 2010 TK7 is. And 2010 TK7 is clearly described as an Earth Trojan, even though it "oscillates about the Sun–Earth L4 Lagrangian point (60 degrees ahead of Earth), shuttling between its closest approach to Earth and its closest approach to the L3 point (180 degrees from Earth)", and originally "may have been oscillating about the L5 Lagrangian point (60 degrees behind Earth), before jumping to L4 via L3." So what is the big difference between 3753 Cruithne and 2010 TK7 that make the latter a Trojan at L4 and not the former? George Fergus (talk) 21:59, 16 May 2020 (UTC)
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)
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
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)
Cruithne is called a quasi-satellite. From the perspective of the dominant body quasi-satellites appear to orbit it in a retrograde direction. Yet the description of its orbit is that of a body in a horseshoe orbit. So which is it? --JorisvS (talk) 11:32, 16 December 2011 (UTC)
Have we cleared this up yet, or is it still open to debate that e.g. it might be a wide-ranging Trojan? 209.93.141.17 (talk) 02:54, 25 September 2017 (UTC)
Lloyd, Robin. "More Moons Around Earth?". Space.com.
This reference no longer exists, but is cited from multiple times in the article. Very good data is available from the JPL sources, so I propose editing out any information the missing source that is not found in anouther source. I will wait a couple weeks before changing the article, so anyone who has another source or has an argument against this edit can make a case. --Kaiomai (talk) 06:25, 24 June 2012 (UTC)
...I belive Alan was klaxoned for saying "two" when it came up again. So Stephen corrected himself. Six Sided Pun Vows (talk | contribs | former account) 20:50, 14 February 2013 (UTC)
Given the theories on the creation of the moon being that early stage solar system had two bodies colliding with a wobble effect the expelled the mass needed to create the moon -- I find it very strange that there appears to be no discussion about whether Cruithne is a left over of that processes. Any mass which was not pull back to either earth or moon would enter into a parallel orbit to the two which is exactly what we see -- Is there any references which discuss such hypothesis? — Preceding unsigned comment added by Sorenriise (talk • contribs) 03:56, 14 September 2013 (UTC)
In case anyone is curious about the spike in page views on and around December 19-20, 2014, it's because Cruithne was mentioned on the popular website thechive.com here. Matt Deres (talk) 14:21, 20 December 2014 (UTC)
Phys.org has just run an article calling it the second moon explicitly (though still in quotation marks in the headline) here, and this has been picked up by Huffington Post. I'm putting these here just in case there's been any revisions of official opinion. Remember Pluto was considered a planet until 2006 so it cannot be said that categories can't be changed, though I do think the official recognition of a second moon would generate some major headlines beyond HuffPo! 68.146.52.234 (talk) 16:54, 26 February 2015 (UTC)
I notice that User:Seattle Skier has removed the comment I made some time ago that 3753 Cruithne' curious orbit (as seen from earth) is an instance of the Coriolis Effect. His reason is that it is "not relevant" to 3753 Cruithne. In a note to me on my Talk page he says "They are completely unrelated effects, other than the fact that both are seen in rotating reference frames, they have no other connection".
The Coriolis effect is a deflection of moving objects when the motion is described relative to a rotating reference frame. This rotating reference frame can be a turn table in your home, a rotating bowl of water in a laboratory, or the motion of water, air, or long-range ballistic missiles over the earth rotating on its axis. It also applies to the geographic paths seen to be taken by artificial satellites that orbit the earth, and it is a Coriolis “force” that keeps geostationary satellites above a fixed position on the earth’s surface. The curious motion of the planets that intrigued the ancients, but are now known, thanks to Copernicus, Galileo and Newton, to be due to Coriolis effects caused by using the earth's orbiting motion around the sun as the frame of reference. When the sun is used as the frame of reference the planets' motions are far more straight forward. The same can be said (and is emphasized in the is article, and on this Talk Page) about 3753 Cruithne’s strange orbit, as seen from earth. But, from what I gather User:Seattle Skier says (unless I am completely misunderstanding his very brief remarks), it seems that Coriolis mathematics does not apply, or is inappropriate at some arbitrary altitude above the earth’s surface. I’m obviously missing a very fundamental principle here. As far as I understand the Coriolis effect, it applies as much to an ant on a turn table watching a fly fly straight across that turn table, as it does to our observations of the motions of the objects in our solar system using our rotating and orbiting earth as the frame of reference.
Could someone please clarify whether or not 3753 Cruithne's motion as observed from earth is an instance of the Coriolis Effect or not. I'm very curious to know the readship's opinion on this. Cruithne9 (talk) 06:36, 22 July 2015 (UTC)
Hi Seattle Skier. Thank you for this extensive explanation. I will need to ponder over it for a while to let the implications sink in, particularly in the light of the remarks about the apparent motion of distant stars as seen from the rotating earth in the "Distant stars" section in the Coriolis effect article, which seems to suggest that any motion (which I would imagine would include objects with an apparent velocity of zero) observed from a rotating frame of reference can be referred to as a "Coriolis effect". (No reference is provided in that section, so I cannot check whether astronomers are comfortable with the term or not, and what they would apply it to, if the term is used by them.) Cruithne9 (talk) 13:04, 24 July 2015 (UTC)
PS. I don't want this to sound as if I am arguing with you. I'm looking for information and enlightenment. So I hope you will bear with me here. As you say above, the Coriolis force is an entirely fictitious "force", as is the Centrifugal "force". Both effects can be explained in terms of simple geometry and physics. I therefore struggle with the dismissal of one fictitious force (the Coriolis effect) in favor of another fictitious force (the centrifugal force) to explaining the apparent behavior of a geostationary satellite. These comments probably sound ridiculous to you, but I would desperately like to know what types of motion viewed from a rotating frame of reference can and cannot be termed "Coriolis" effects. Cruithne9 (talk) 14:01, 24 July 2015 (UTC)
PPS. I think I may have discovered why we seem to be talking at cross purposes. When an object moves over the earth's surface (and is partially or wholly detached from that surface) it seems to follow a curved path. For someone observing that curved motion, and who is unaware that the earth is rotating, it would seem as if the object is subject to a sideways force causing it to deviate from traveling in a straight line. One can calculate the force that would account for this motion, and call it a "Coriolis Force". But it is an entirely fictitious force. The formula you use applies to this situation, which a special case of the Coriolis effect. When a straight-line motion across the solar system is viewed from our orbiting perspective, the path would also appear curved. The formula needed to calculate the "force" that might be responsible for that curved motion would be different from the one you present above. Things become mathematically horrendously difficult if the "real" motion is circular or elliptical round the sun. But that does not mean that the distorted motion as viewed from the orbiting earth is not an instance of the Coriolis "effect".
3753 Cruithne's bean shaped orbit in the vicinity of the earth is not due to Coriolis Forces (or, let's say, it would be foolishness to calculate them, as they would be unique to Cruithne, and applicable nowhere else in the universe). But that does not mean that its motion as seen from earth is not an instance of the Coriolis Effect. I hope this makes sense. Cruithne9 (talk) 20:29, 24 July 2015 (UTC)
PPPS. Hi Seattle Skier. I would like to make just another point. The formula you provide for the Coriolis Force applies to objects moving horizontally over the earth's surface, and is used extensively in meteorology. That force is maximal at the poles and zero on the equator. But consider a bullet shot absolutely vertically upwards. Ignoring the influence of air currents, that bullet will come down slightly to the west of where it was fired from (both north and south of the equator), except at the poles, where it would fall down back into the barrel from which it was fired. The deflection is maximal on the equator. So here the Coriolis forces that account for this phenomenon have the opposite effect to the ones predicted by your formula. I only mention this to emphasize that the Coriolis Forces are instance specific, and do not define the Effect. My apologies for my ramblings on like this. Cruithne9 (talk) 03:54, 25 July 2015 (UTC)
Hi Seattle Skier. You present the image File:Horseshoe_orbit_of_Cruithne_from_the_perspective_of_Earth.gif as a sort of "proof" that Cruithne's bean-shaped motion relative to the Earth is derivable from simple geometry, and geometry alone, without needing any physics or Coriolis "forces" or whatever. But exactly the same can be said of all the following examples of the Coriolis effect taken from the following clips in the Coriolis effect article:
and this animation clip of a cannon ball being fired from a rotating platform.
In each case the motion seen by an observer on the rotating non-inertial frame of reference can be explained even more obviously, simply, and in its entirety, by geometry, without recourse to any physics, or related sciences, than your example of Cruithne's orbit, when viewed from an inertial (stationary) frame of reference. I see absolutely no difference between your example of the (File:Horseshoe_orbit_of_Cruithne_from_the_perspective_of_Earth.gif) and the examples given in the Coriolis effect article (and other sources) of the "genuine" instances of the Coriolis effect.
Furthermore, if I understand you correctly, you maintain that the formula for the magnitude of the Coriolis Force, , defines the Coriolis effect. But consider this situation. A spot of light from a laser pointer is moved at a uniform speed, in a straight line across a rotating turntable (the spot of light does not need to move across the center of the turntable). If the surface of the turntable is light-sensitive, the spot will leave a trail on the surface which is curved to exactly the same extent as the trail left by a ball rolled across the turn table at the same velocity. It is difficult to conceptualize a real physical force that will have such a profound effect on a spot of light. Now move the spot of light in an ellipse across the turntable. The ellipse’s dimensions are a scale model of Cruithne’s orbit around the sun, with the turntable’s axle in the position of the ellipse’s “sun”. It is timed so that the ellipse is completed in exactly the same time as one rotation of the turntable. A bean shaped trail will be formed on the turntable, which is a miniaturized version of the orbit of Cruithne as seen from earth. If you acknowledge that this is an instance of the Coriolis effect, then the one we see in the sky must also be due to the Coriolis effect resulting from our orbit round the sun. Cruithne9 (talk) 09:39, 2 August 2015 (UTC)
Hi Seattle Skier. Very many thanks for the time and trouble you have taken to extensively respond to my concerns and misconceptions. I entirely agree that I got the bullet shot vertically upwards wrong. I should have realized that it would indeed come back down straight into the barrel of the gun from which it was fired, whatever part of the earth it was launched from. It was 3 a.m. in the morning when this idea occurred to me. My apologies. Though the bent trajectories bullets follow upwards and downwards are fascinating examples of the effects of the rotating earth.
Although I have no idea of how much of this discussion should be continued on the Talk pages of Wikipedia, because, much of this discussion could be resolved very quickly and efficiently through a face-to-face interaction, and then posted on this page in a few sentences, I feel I have to respond to some of the comments you have made.
Firstly, all of the texts explaining the Coriolis effect, including the Wikipedia article on the subject, start with the example of a rotating turntable or carousel, across which a pencil line drawn with a ruler (by a person outside the turntable) or balls tossed across the carousel either by a person on the carousel or by a person outside the carousel seem to follow curved trajectories when viewed by the person on the carousel.
Consider a rotating carousel (or merry-go-round), which, seen from above, is rotating clockwise. We will call the person on the carousel the “rotating” person, and the one on the ground outside the carousel as the “stationary” person. Any ball thrown across the carousel by either person follows a straight line as seen by the stationary person. But the rotating person will always see a curved trajectory. From the rotating person’s point of view it therefore seems that there is a force that acts (horizontally) perpendicularly to the ball’s motion to cause it to deviate from the Newtonian straight-line motion. This in not a real force, but an artifact of the observation relative to a non-linear rotating reference frame. (This is a direct quote form a Physics text book. The Wikipedia article on the Coriolis effect calls it a fictitious force, as do several other sources at my disposal). The entire effect can best be explained in terms of simple geometry, which, in your terms, if I understand you correctly, means that it is NOT an instance of the Coriolis Effect.
Where a “real” force comes into play (and cannot be explained in terms of simple geometry) is if the rotating person tries to move from point A to point B on the rotating carousel. If point A is close to the center of the carousel, and point B is near the periphery, then, if this person sets out in what he imagines is the shortest distance between the two points, he ends up to the left of his target. In order to reach point B he has to exert a sideways acting force to move him more and more to the right as he moves outwards towards B. On the carousel he will have traced a straight line trajectory, but according to the stationary person on the ground outside the carousel he will have moved along a curved path which can only have been caused by a sideways force. This force (or acceleration) is indeed real, because it required the expenditure of energy from both the rotating and stationary observers’ points of view. Is this the only instance of the Coriolis effect you would recognize as such?
If the turntable and carousel examples provided in all the introductions to the texts on the Coriolis effect are genuine, prototypical instances of the Coriolis effect then, by extension, any Newtonian motion beyond the carousel, viewed by the rotating individual, will also subject to Coriolis effects. Thus a ball thrown away from, or beyond, the carousel’s rim will also follow a curved as seen from the carousel. Indeed if it stays in the air for several turns of the carousel it will appear to follow an outwardly spiraling trajectory. In all cases the motion can be explained in terms of simple geometry from the point of view of the stationary observer. But if Newtonian motion across the carousel is correctly described as Coriolisean by the rotating observer, then the motion beyond the carousel must also be due to the Coriolis effect. It then ineluctably follows that motion observed from our orbiting earth of the planets and other objects in the solar system are also affected by the Coriolis effect. The fact that the complicated motions observed from earth are best resolved by translating them into the motions that would be seen by an individual in a stationary position in relation to the sun does not negate the fact that from the earth these motions are due to Coriolis effects, even though the stationary observer would ascribe them to simple geometry. The Coriolis effect does not exist for a stationary observer. But they are very real for an earth-bound observer unaware that he is on a huge 3 x 108 km diameter carousel centered on the sun.
I know that you have said above that this nonsense, but you have not explained why it is nonsense, nor given any examples of when and how the Coriolis effect applies. For instance, are you suggesting that the turntable and carousel examples used in all the texts explaining the Coriolis effect are simply “lies to children” (to quote Terry Pratchett)? What would your interpretation of these examples be? In the “Visualization of the Coriolis effect” section of the Coriolis effect article in Wikipedia a puck of dry ice is slid across a bowl of spinning water. This puck follows an elliptic track (as seen by a stationary observer) across the parabolically curved surface of the rotating water in the bowl, although it bounces back and forth off the rim of the bowl. The Coriolis motion as recorded by a camera mounted on the rim of the rotating bowl is uncannily reminiscent of the orbit of Cruithne as seen from earth. Cruithne9 (talk) 12:39, 30 July 2015 (UTC)
Thank you very much. That makes it a it a lot clearer and understandable, and I am happy to close the discussion. Cruithne9 (talk) 05:26, 5 August 2015 (UTC)
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