This is an archive of past discussions about Ecliptic. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page.
Is the ecliptic the plane that contains the Earth's orbit or the apparent circle described by the Sun as viewed from Earth? If it's the plane, you cannot say that the plane intersects the celestial equator in two points as two planes intersect in a line. Please clarify before I try my hand at an edit. Danielcohn05:13, 30 November 2005 (UTC)
I agree with the most previous comment. This page is quite useful, but it could use some refinement. I think it would be better to make clear early on that the Ecliptic is a circle inscribed on the celestrial sphere, because, technically, the intersection of a plane through a sphere is still a plane.
Not sure if this question has been addressed elsewhere, but my thinking is that it works either way. If we think in terms of planes, then the intersection of the ecliptic and equatorial planes forms a line we can call the equinox: streching in both directions from Earth infinitely into space. The segment of this line facing the Sun at the time of the March equinox, we could think of as the March (or vernal in the Northern hemisphere) equinox line segment. The other line segment is the September equinox line segment). The point where this line interesects the celestial sphere would be the point of the equinox (either vernal/autumnal/March/Septmeber depending on the point behind the Sun at the time of the equinox). All of these are distinguished though related from the date-time equinox as a point in time related to the position of Earth relative to the Sun. If we instead think of these as circles inscribed on the celestial sphere as projections of the ecliptic and equator onto the sphere then they immediately define a point.--Cplot 03:13, 1 July 2006 (UTC)
Correct, said shorter: the intersection of the ecliptic plane and equatorial plane is a line. But what we see is an intersection of these planes and this line with the celestial sphere. Both the ecliptic and the equatorial plane intersect as circles, while the line intersects in two points: the both equinoxes. --Tauʻolunga06:48, 1 July 2006 (UTC)
first point of aries
I removed a paragraph or so about the first point of aries. The explnation seemed to have lost it's context from other edits and the discussion seemed more appropriate for the article on first point of aries.--Cplot 03:50, 1 July 2006 (UTC)
I do not think that to be a good idea. Admittedly when I wrote that paragraph a long time ago I kept it short by intention — because I did not want to reduplicate the story told in that other article or the zodiac article or the precession article. But having it short does not mean that is superfluous. The information about the vernal equinox given there is still a basis, needed to understand the next paragraph about the Sun. And those people who think it is too short, well they can go to the other articles.
I am sorry to say, but the changes you made to this paragraph before that were very confusing. I had to revert it. --Tauʻolunga07:10, 1 July 2006 (UTC)
disputed reversion
Tauʻolunga, I don't understand the edits you made. What exactly was missing from the text that I revised that was needed in the following section on the Sun? Could you please clarify? --Cplot 18:39, 1 July 2006 (UTC)
In the next chapter (ecliptic and Sun), the equinoxes and solstices are described and the signs in which they occur. People should know by then that these are not equal to the actual constellations. As such some words about the precessional shift should remain. Also the table with the shifts in which modern constellation they occur does not make much sense without it. So I really think you should bring it back, shortened if you want (although it was already very short). After all, I am also not removing things from you in the zodiac article when I think they should not really be there. I suggest we focus on astronomy in this (ecliptic) and astrology in that (zodiac) article. As such I also strongly object terms as 'tropical coordinates' and 'tropical zodiac': they do not exist in astronomy. Just write: …shift eastwards measured in ecliptic and equatorial coordinates. Dot finished, leave the zodiacal coordinates to the zodiac article.
Next be aware that the proleptic year -67 is not equal to 67 BC, it is 68 BC, as the year 0 does not exist in historical counting. Likewise -1865 is for sure not 865 BC (sic).
The latitudinal size of the zodiacal signs is undefined. As such this line should not be removed: …undefined size in latitude (although sometimes 8° is taken, the largest latitude the classical planets can reach (Venus at some inferior conjunctions)).
The line: …typically use other coordinate systems today for various culturally and technologically dependent reasons (for exa… A little bit dramatic, and its no-use is already mentioned in the very last chapter. I think it is more important here to stress here that when astronomers talk about zodiacal constellations, they recognize 13 of them of different sizes as opposed to 12 astrological of 30° longitude each.
If you cannot agree to this, then I think we have to put up both versions and ask the community which they prefer. --Tauʻolunga20:35, 1 July 2006 (UTC)
Thanks for the elaboration. I see much more clearly what you're saying now. I had not introduced that text; I only cleaned it up because I think it had become disjointed from many edits. I think there's certainly room there to include all the information we're talking about betwen us.
The mention of the zodiac was already there. I was simply trying to make it coherent and consistent with the more elaborate description in the zodiac article. I'm fine with only talking in terms of constellations, but the mention of equal 30° zones suggests zodiac signs and not zodiac (or ecliptic constellations). The mention of zodiac and 30° zones may be confusing matters and perhaps use of the ecliptic coordinate system would simplify things.
Having said that, I do think one important role for the ecliptic is in defining the center of the zodiac region (whether you think of that in terms of a full 90° of latitutde; the historicl 8° of latitude encompassing orbitabl paths of the naked eye planets; or something in between like 17° to encompass all known Solar system planets).
I'd be fine with removing the line about other coordinate systems (especially if the zodiac issue is cleared up per my previous point).
Finally, on the years mentioned. I misinterpreted those dates because no units were provided. If julian years are used I think it would be important to specify that clearly. Though I think Gregorian years would be familiar to a wider readership (and not need further explanation). The one you mention was a typo; I'll fix it. Thanks for the elaboration. --Cplot 03:56, 2 July 2006 (UTC)
One more correction. The dates aren't simply 1 year different, but I think that since the Julian calendar is a sidereal calendar versus the Gregorian tropical calendar, the years could be quite a bit different. But perhaps -67 meant 67 years before 1 AD: it's not entirely clear. There's no citation so I can't track down the source of the information. Since the movement of the equinox through these constellations is rather rough anyway, perhaps we can just leave the dates as those approximations or shitfed by one year as you say. Either way I think it's more important to make it clear what calendar it's referring to otherwise there's no precision at all. --Cplot 03:56, 2 July 2006 (UTC)
No, what you tell here is wrong. Read the calendar articles, I copy from: "The Julian calendar was ..... probably designed to approximate the tropical year,... " Western calendars have done never anything else than follow the tropical year. It is customary in astronomy to use Gregorian after 1582 and Julian (proleptic) before and that 1 BC = 0, 2 BC = -1 etc. The book (which is quoted) is clear in that. Perhaps I should have stressed it more in the article. Well, can still do it. --Tauʻolunga08:17, 2 July 2006 (UTC)
That's fine. No need to get too upset about it. My point was mainly that we still need to have units there: raw negative and postive numbers don't really look like calendar years. By sidereal, I merely meant that the Julian calendar much more matches the sidereal year than the Gregorian calendar does: so the dates would be slightly different. It probably doesn't matter if we're listing years there. I just happened to write a note about this at the manual of style talk page. It looks to me that you're refering to the Astronomoical Julian calendar. In any event, I think diverting from the proleptic Gregorian or Julian calendars should include some notation of the calendar units used. --Cplot 08:55, 2 July 2006 (UTC)
astronomy and astrology
The last paragraph under "Ecliptic and Sun" appears to mix astronomy and astrology; I think it should be rewritten. Judging from the dates, it is talking about the astrological signs of Cancer, Capricorn and Libra (I changed the links to point to these accordingly), but from the rest of the wording it sounds as if it's talking about actual positions of the sun in constellations. The periods of the astrological signs differ significantly from the presence of the sun in the corresponding constellations. Joriki06:10, 4 July 2006 (UTC)
reason for movement
Am I correct in understanding that the apparent east-to-west movement of the celestial sphere, and consequently the apparent west-to-east movement of the sun along the ecliptic, is essentially due to parallax, and the 'counterclockwise' revolution of the earth around the sun? If so, I think it would be good to mention this in the 'ecliptic' article so that the 'parallax' article can be linked. I'm new to Wikipedia, and astronomy, and would like a discussion (and hopefully confirmation) before attempting such an 'edit' myself. 149.99.132.243
I would say the second movement (apparent west-to-east) is most directly the result of parallax. However, the movement of the celestial sphere relates to the difference beteen a sidereal and tropical year, so that the Sun's position at the same point in a tropical year (like either equinox or solstice) is not the same apparent position relative to the celestial sphere as the respective point in the previous year. This difference between relates to the eccentricities of Earth's position and motion more than the position and motion of the Sun relative to the other stars.--Cplot 03:13, 1 July 2006 (UTC)
The celestial sphere is defined as from the centre of the Earth and as such not subject to any parallax whatsoever. The daily westwards movement of the Sun (and all other objects) is due to the rotation of the Earth around its axis. The yearly eastwards movement of the Sun due to revolution of the Earth in its orbit around the Sun. That is all, no more, no less. --Tauʻolunga06:40, 1 July 2006 (UTC)
I agree with Cplot, the apparent west-to-east motion of the Sun and its apparent position on the ecliptic and celestial sphere is the result of parallax. That is, the relative position of the Sun to other stars changes due to our (the observers on Earth) motion (revolution of the Earth in its orbit). Many stars change their apparent position on the celestial sphere due to parallax. As far as the apparent east-to-west movement of the celestial sphere, I believe 149.99.132.243 was referring to (and I may be wrong about their question) the daily motion of the celestial sphere which is, as mentioned by Tauʻolunga, due to the rotation of the Earth around its axis. I do not think they were asking about the precession of the equinoxes. AikBkj18:37, 27 October 2007 (UTC)
Ecliptic and planets
The table comparing planet orbits to the ecliptic plane gives interesting information. While digesting it, I missed the inclination of the Earth's orbit (ecliptic) relative to the Sun's equator. −Woodstone (talk) 12:26, 24 May 2008 (UTC)
What about the greater orbital eccentricity of the dwarf planets? Could reference to them be expanded into a paragraph which discusses contending theories why Pluto, Eris, Haumea and Makemake all have eccentric orbits?
Calibanu (talk) 01:52, 21 January 2009 (UTC)User Calibanu
Secondly, does this differ markedly from the asteroid belt, in which context any peturbations would probably be attributable to Jupiter's gravitational influence on their formation and orbital configurations?
Calibanu (talk) 01:54, 21 January 2009 (UTC)User Calibanu
A good change
The new diagram is much better. My concern with the ITCZ (Intertropical Convergence Zone), showed as a line of clouds north of equator (in the old diagram) was that it was leading to confusion, since it is a changing feature along the year: those clouds use to be north and south of equator according to the time of the year. And I apologize for my own error regarding the earth and celestial axis, which, obviously, are coincident. Thank you. --Fev (talk) 00:18, 7 August 2009 (UTC)
Replacement for deleted image
User Fev deleted the ecliptic image from the article "until image is corrected (se discussion page)". His reasons are on File talk:AxialTiltObliquity.png, he said there was an "evident mistake", "The North Celestial Pole in the image is, actually, the North Terrestrial Pole. Then the Intertropical Convergence Zone (ITC) north of the ecuator would be correctly located. --Fev (talk) 04:05, 25 July 2009 (UTC)".
This objection itself appears incorrect. It's very well known that the (north) celestial pole is the pole of the celestial equator. Terms used here originate from the traditional metaphor of the imaginary celestial sphere, with its celestial equator directly above the terrestrial equator. Thus, the north celestial pole is on the same axis as the terrestrial north polar axis (pointing northwards beyond the earth's surface). The diagram was correct in its celestial indications and in its captions.
(By the way, the north celestial pole is quite different from the north pole of the ecliptic. That is about 23.44 deg. away from the north celestial pole, and located on a celestial meridian (colure) 270 deg east (or 90 deg. west, the same thing) of the celestial meridian or colure that passes through the vernal equinox, i.e. intersection of the equator and ecliptic where the ecliptic heads north-east.)
Fev stated a concern that the Intertropical Convergence Zone north of the equator
should be properly located. This is a geophysical matter, not relevant to the subject of the article which is the (celestial) ecliptic.
But the deleted image is far from ideal. Nearly all of its geographical detail is irrelevant. The use of an actual photograph of the Earth from space clutters things up, and gives a misleading visual impression that there might be a spatial correspondence between the position of the celestial ecliptic and some defined geographical points on the Earth's surface -- but there is of course no such correspondence at all, because of the Earth's rotation. So, for example, the vernal equinox on the diagram looks as if it is located overhead equatorial South America more or less. In truth, this celestial point appears to circulate westwards around the entire earth's equator once per (sidereal) day and is not particularly associated with equatorial South America. So maybe geographical detail on the image is not aligned correctly with the geographical detail on the real Earth, but it would be better nt to have the geographical detail at all.
Better to replace the old image by a diagram that gets rid of the clutter, and just shows the earth's equator and pole along with their celestial counterparts and the ecliptic plane itself, represented as usual by a circle where its plane cuts the imaginary celestial sphere.
I did a search in Wikimedia Commons for a suitable alternative diagram. The nearest I could find to what is needed is "Image:Axialtilt.gif". This seems to improve on the cluttered space-picture, because it more clearly separates the celestial and the geographical parts. I have added it as a replacement, along with a few explanatory words (to try and avoid misunderstanding about the remaining geographical detail and rotation).
There's also a useful-looking diagram from German Wikipedia which might possibly do better. It would need to be redone to give English captions. I don't have graphical skills, but for any that want to fix it, here are the translations of the German captions:
Himmels-Nordpol == North Celestial Pole //
Himmels-Equator == Celestial Equator //
Fruehlingspunkt (oder Widderpunkt) == Vernal :Equinox (or First Point of Aries) //
Ekliptik == Ecliptic //
Erde == Earth //
Sonne am 21.3 (or 21.6 or 23.9 or 21.12) == Sun (position) on 21 March (or 21 June or 23 Sept or 21 Dec).
Also, the Greek letters which might be retained or discarded stand for angles as follows:
epsilon (ε) == obliquity of the ecliptic,
alpha (α) == right ascension,
delta (δ) == declination, and
lambda (λ) == (Sun's) longitude in the ecliptic.
I also attempted to clarify the lead paragraph. There was one very obscure sentence
"The apparent path aligns with the planets throughout the course of the year.", I took it out but maybe a clearer version could go in.
Terry0051 (talk) 18:12, 25 July 2009 (UTC)
I don't think the definition given in the article is all clear, because the apparent path that the Sun traces in the sky includes it's path throughout the day, and if I'm not wrong, the Ecliptic is only it's apparent path during a year.
Could someone perhaps make this article a bit simpler because as an encyclopedic article it makes no sense to people who have come on to try and learn something. its like an excerp from a text book - which defeats the point of the article. AG. —Preceding unsigned comment added by 217.42.128.120 (talk) 23:34, 23 September 2008 (UTC)
I agree that the definition is unclear, in particular the second sentence "As it appears to move in the sky in relation to the stars, the apparent path aligns with the planets throughout the course of the year". Does "as" here mean "because" or "while"? And does it move, or apppear to move, in relation to the stars? No it is fixed. The fact that it is curved when shown on flat star maps does not mean it "moves". I don't know enough about astronomy to edit the definition, but it is confusing, and needs correcting. Alpalfour (talk) 06:55, 27 September 2008 (UTC)
Actually except for the intro this is a good article and does not deserve a C. That is only my opinion. Also these wierd terms come from ancient Greek astronomy so we need to dip into that. The ecliptic is the path of the sun. Period. Part of the confusion is the term "apparent." It has people looking all around for the "real" motion. There isn't any, what you see is what you get. The term really meant is relative velocity. The path of the sun is not illusory or fantasmic, it really does go around the Earth and not apparently so. But, we only see it from our point of view so its velocity seen by us is its relative velocity, which is around the Earth. If you are sitting in a train and the train starts up, how much momentum do you acquire? Wrong. None is the answer; moreover, you are not accelerating and are not even in motion. From your point of view you are at rest but the objects on the Earth's surface have an acceleration and momentum relative to you. So, let's use relative for apparent, hey? The literature has not caught up with Einstein. I can get to this article but not right away. "Ecliptic" by the way is correctly explained further down in the article. It does come from eclipse, which is partly caused by the path of the sun (Greek view). Somebody who knows the topic needs to think about presenting it to those who do not. Think rather than thimk. Take a shot. What's the worst that can happen? What's the best that can happen?Dave (talk) 13:13, 25 October 2008 (UTC)
I too find the definition — “path of the sun through the sky during the year” — extremely puzzingly (though it’s common, not only in wikipedia). The problem with this definition is: what about, you know, the daily circular motion of the sun in the sky? As in, the one all laymen know about?
As it turns out, the circles the sun traces in the sky are not the same through the year. They change a little (almost 1°) every day. So the “path of the sun on the sky in a year” is a complex spiral made of 365 turns. The stars also happen to circle the sky every day, but the circles they make don’t change (noticeably in a human lifetime). This is what people mean when they talk about the path of the sun “against” the stars: though the sun is revolving in a day, the stars are revolving too, so that you can say the sun is “in” a constellation—but which constellation exactly is something that changes slowly during the year. I could only visualize that “path” as a circle with the help of this appplet and video. 189.74.109.213 (talk) —Preceding undated comment added 21:23, 5 February 2011 (UTC).
Sun Coordinate System Better?
I find the first sentence "The ecliptic is the apparent path that the Sun traces out in the sky during the year" unhelpful. Seen from the Earth's coordinate system, the Sun traces out not a single path but moves in a wide band (high-low) over the course of a year.
Would it not make more sense to consider everything from the coordinate frame of the sun? In that case the intro would read "The ecliptic is the path that the Earth traces out revolving about the sun during the year" or "The ecliptic is the plane of the solar system". This seems to me to be a much simpler explanation that trying to consider orbits from the Earth which is spinning on an inclined axis whilst revolving about the Sun.
John Muir (talk) 12:25, 12 December 2010 (UTC)
The path referred to is the path one would see if they looked at the sun at the same sidereal time every day. It's a discrete path, with points at the vernal equinox, summer solstice, autumnal equinox and winter solstice respectively. It's taken me a long time to "visualize" this in my head. I totally agree with your sentiment. I'm not sure how many people would understand that sentence, esp. since it involves the concept of sidereal time and that took me forever to wrap my head around. Now it seems so simple! I think some kind of request for help from other editors might be needed here. I will keep this in mind. Now that I understand the ecliptic it has opened up a wide range of understanding of celestial mechanics. The fact that the earth "wobbles" with respect to the sun throughout the year has caused me much confusion. --TimL (talk) 13:36, 14 July 2011 (UTC)
I have to agree with the initial criticism, and in spite of the discussion above, the article's definition is still very confusing. It seems to be one of those definitions that is perfectly clear to anyone who already understands the phenomenon, but is totally opaque to anyone who doesn't. And the charts and video don't help much: what's needed is an earthbound explanation. The problem is with the phrases "apparent path" and "in a constellation." In ordinary language, these phrases have a strongly intuitive meaning. The "apparent path of the sun through the sky" is that the sun in the morning rises in the east, climbs to an overhead point in the sky, and then travels down the sky to set in the west. This daily "apparent path" of the sun through the sky obviously isn't what the ecliptic is -- if it were, there would be 365 different ecliptics. So if the ecliptic isn't this "apparent path," what "apparent path" is it? Likewise, how can the sun be "in" a constellation? Suppose I'm told "the sun is in Aquarius." So I go outside and look up at the sun, and of course I can't see Aquarius because it is daytime, so how can the sun be "in Aquarius?" Or if I go out at night and look up and see Aquarius, the sun isn't there because it is night, so how can Aquarius have the sun "in" it. These perplexities may seem absurd to those who already understand perfectly well what the ecliptic is, but I assure you that many educated an intelligent people are mystified by the standard definition of the ecliptic as "the apparent path of the sun through the constellations of the zodiac" exactly because they cannot reconcile that definition with the common understanding of "the sun's path" and something being "in a constellation" which I've described. If this article could clear up this confusion, it would be more useful to the layperson than anything I've so far read on the subject in any on line or printed source. — Preceding unsigned comment added by 99.139.226.156 (talk) 17:03, 17 July 2011 (UTC)
Well everything you said was my point really. To your question; the sun can be in Aquarius if one knows where Aquarius should be in the daytime sky. That's really the only way to tell. You have to know where the zodiacal constellations are day or night. If you looked at the sun set, gradually it would get darker and eventually you would see the constellation ahead of the sun (the constellation the sun is "heading to") also setting. You could than infer what constellation the sun is "in" (really "near") as long as you know the order of the constellations in relation to each other. Throughout the year if you examined the sky after each sunset you would notice that each day the zodiacal (or ecliptic) constellations are setting later and later and in fact seem to rotate full circle throughout the year. Each month a different constellation will have shifted westwards and be the one in view just after sunset once it is dark enough to see the stars. I'll have to put this on my todo list as far as making a intro a layperson can understand. I imagine it won't be easy. Thanks for your feedback. (I learned most of what I know, by the way, via a program called Emerald Chronometer for the iPhone and iPod Touch. There is also Star Walk which lets you point the phone at the daytime sky and see what is actually there (plus a virtual ecliptic line), though obscured by daylight. I don't know if there is anything similar for a PC or Mac)--TimL (talk) 18:54, 21 July 2011 (UTC)
Thanks for the clarification. If I understand, another way of putting it is that if you could see the stars in daytime, the sun would be among the stars of Aquarius. I hope you'll put this in the article. I think the phrase "path through" still needs some explanation though -- I at least still find that idea hard to envision. — Preceding unsigned comment added by 99.139.226.156 (talk) 14:14, 24 July 2011 (UTC)
Shifts in Ecliptic
The Sun and our moon was known to be not always at 23 to 26 degrees in the point of solstice meridians: They were located as high or low as 18 degrees to 28 degrees latitude both north and south of the celestial equator, about 5 degrees off the normal point every few years. The Moon has a 18.6 sidereal year cycle, while the Sun is in a 11.5 sidereal year cycle from what I heard, so that astronomers keep a much close precise track of the orbits of them and the planets when they travel on the ecliptic across our night sky. 71.102.3.122 (talk) 09:47, 12 November 2011 (UTC)
It is somewhat strange that the moon in the second picture is lit by the sun in a manner that half of it (to the right!) is bright, although the moon is placed between the camera and the sun. I would expect a very thin crescent at the top of the moon, as most of it should be black,
due to the latter stated fact (it is between the sun and the camera).
I believe this is not a real picture.
Pelegs (talk) 10:20, 26 November 2011 (UTC)
As the caption says, the moon in that picture is not lit by the sun, but the earth. It is indeed a real picture. TimL (talk) 09:36, 27 November 2011 (UTC)
And what does that have to do with the original question? The problem is not the quality of the image. The quality is just fine. --TimL (talk) 22:56, 28 November 2011 (UTC)
Ecliptic vs. plane of the ecliptic
This article seems to be trying to describe both the ecliptic and the plane of the ecliptic, which has its own article. I've rewritten the lede to fix this, but some of the material in this article should be moved to that one. -Jason A. Quest (talk) 15:48, 24 December 2011 (UTC)
I propose that we merge these two pages, and rework them generally. This is probably internet's most read article on the ecliptic, and it should be a little more authoritative. I propose these two images
to replace the current images. We should correct the above-mentioned problems, and move some information (which is only indirectly related to the ecliptic) from this article to more appropriate articles.Tfr000 (talk) 13:50, 16 March 2012 (UTC)
I generally agree. I think one of the images from the "Plane of the ecliptic" article that shows other planets not lying in the plane of the ecliptic be included. Jc3s5h (talk) 14:20, 16 March 2012 (UTC)
I would like to find a couple of public-domain photos showing the Sun, Moon, and a few planets arranged roughly along the ecliptic. During planetary conjunctions, you occasionally see such photos, taken at sunrise and sunset. Also, a good photo of the Zodiacal Light might be appropriate. Tfr000 (talk) 19:42, 16 March 2012 (UTC)
I presume you mean the graph with the caption that begins "Inclination of the ecliptic over 200,000 years". I have no idea if the book this graph is based on is considered a good book or not, but the graph seems internally reasonable. The graph is showing changes in the inclination of the ecliptic. The value treated as 0 is the inclination in the year 101,800 CE.
A problem with the graph and caption is that it does not state what the reference frame is. How is the ecliptic plane of the year 101,800 realized? Fixed stars? An offset from the invariable plane? Jc3s5h (talk) 19:18, 24 March 2012 (UTC)
Yes, it could probably use a better caption. The reference plane for the data used by the author was the ecliptic of 1800 - in other words, it was the inclination of the ecliptic to its own orientation at 1800. This causes a discontinuity at 1800; inclination doesn't go from to - when it crosses 0, it just stays ; this is a little confusing so I just re-interpreted the data to the ecliptic of 100,800 by adding the value at that date to all of the others. I hope that's not considered "original work". The book is available at Google... maybe we should link to it:
It is now clear to me based on your comments and the caption an hindsight that this is a graph of the rotation of the inclination of the earth over time. I thought it was a graph of the change in the inclination itself over time compared to some odd reference frame. Is this correct? --TimL (talk) 13:35, 25 March 2012 (UTC)
OK, so re-reading the caption and studying the graph it is obviously the precession of the earth's inclination over time, I think this is a bit too technical (and perhaps a little obscure) for the article. I think a statement that the nodes of the earth's orbit are very stable over time would be sufficient. --TimL (talk) 13:44, 25 March 2012 (UTC)
Perhaps it's too technical. One thinks (or should, anyway) of precession (the changing of the "origin" of celestial coordinates over time) as the intersection of two planes, the ecliptic (i.e. Earth's orbit), and the equator, both of which are moving. The equator moves a lot over time (the vast majority of what is called "precession"), the ecliptic moves only a little. The intent of the graph was to show that the ecliptic (i.e. the plane of Earth's orbit) moves only a few degrees over 200,000 years, while at the same time the celestial equator is rotating all over the sky every 26,000 years. (not that obvious in this article, because it's not about the equator). What we really need is an animation... worth 1,000 words and all that. Anyway, I included the sentence: "Of the two fundamental planes, the ecliptic is closer to unmoving against the background stars, its motion due to planetary precession being roughly 1/100 that of the celestial equator." to describe the same thing, so... yes, maybe that's sufficient. Tfr000 (talk) 17:28, 25 March 2012 (UTC)
Astronomical Almanac provides 2 definitions but article only recognizes first. "In the constellations" should have a citation because astrologers may take issue with this.
Fails because of the file noted under criterion 6.
Pass/Fail:
Passes, all criteria have been met. FourPlanetSunset hao annotated.JPG no longer has copyright issues.
Since the article fails at the moment, but there is a good prospect that the copyright status of the file mentioned above can be clarified, or a substitute image found. I'm placing the article on hold. Jc3s5h (talk) 15:27, 27 June 2012 (UTC)
The lead section
I wrote it this way in order to avoid all of the handwaving (seen above here on the talk page) attempting to explain the difference between the daily motion of the Sun across the sky, and the yearly motion against the stars, or between the motion higher in the summer/lower in the winter and the motion against the stars. These seem to be difficult for some people to differentiate. Probably it could be elaborated and made clearer, so be bold, editors. Tfr000 (talk) 12:56, 30 June 2012 (UTC)
actually ecliptic is the apparent motion of the sun around the by keeping earth at its centre .it has two points called equinotical points — Preceding unsigned comment added by 116.73.217.115 (talk) 09:47, 22 July 2012 (UTC)
It also, for a very brief period of time (About 18 hours a year), touches the border of Cetus
I have been thinking about this. At first, I thought it must be due to nutation. But nutation is a motion of the Earth's axis, and with it, of the RA/dec equatorial system. The ecliptic is not involved - the constellations and the ecliptic do not move with nutation. What we're looking for is a motion of the ecliptic vs the constellations. The ecliptic only moves very slowly due to planetary perturbations, the so-called "planetary precession". There may be a periodic perturbation that moves the ecliptic slightly with a period of about 1 year, however... the Astronomical Almanac's definition is: the mean plane of the orbit of the Earth Moon barycenter around the solar system barycenter, i.e. any periodic perturbations are not considered. And Meeus states very clearly in chap. 22 of Astronomical Algorithms that there is no "true" vs "mean" ecliptic unlike the celestial equator, which has the periodic motion of nutation.
The author (166.216.128.152 ) of the above quote writes I thought this was worth note, it can be confirmed with starry night planetarium software. Unless Starry Night is doing perturbation analysis of Earth's orbit, it must be wrong.
1. The mean plane of the orbit of the Earth-Moon barycenter around the solar system barycenter. 2. The apparent path of the Sun around the celestial sphere.
How to explain it.... the equatorial coordinate system is tied to the Earth - it is basically a projection of longitude/latitude into the stars. So it moves with nutation, the same way as the Earth does. This means the right ascension/declination of everything, including the ecliptic and the constellation boundaries will change in RA/dec, but won't move relative to each other due to nutation. What we need in order for the ecliptic to touch Cetus is either for the ecliptic to move against the stars - which it does, due to planetary precession, but only very slowly over thousands of years, or, as I neglected and Jc3s5h pointed out, if the actual observed position of the Sun moved into Cetus for any reason. Now, Meeus says, in chap. 24, that the ecliptic latitude of the Sun is never more than 1.2 arcseconds vs the ecliptic of date, i.e. the ecliptic updated for planetary precession to its position at that instant. So the Sun is never more than 1.2 arcseconds off of the ecliptic, therefore if the border of Cetus is father than that from the ecliptic, the Sun is never in Cetus. Tfr000 (talk) 17:39, 29 June 2012 (UTC)
I'm doing some work on this, but it would probably count as original research, so would only give us a hint about what we should look for in reliable sources. I have found a C program that takes a RA and declination, precesses it to 1875 when the constellation boundaries were defined, and runs through a list of constellation boundaries until it finds the right one. Although the difference would probably be insignificant, it would be interesting to know the exact date and reference frame used for the constellation definitions in 1875. Anybody happen to come across that? Jc3s5h (talk) 17:53, 29 June 2012 (UTC)
Well I also just did some Excel calculations from the 1875 constellation boundaries precessed to various epochs, and the obliquity of the ecliptic at those epochs based on Laskar's 10,000 year formula, and as far as I can calculate (all using Meeus' methods), the ecliptic was indeed outside of Cetus in 1875, but since 1935 or so, it has been across one corner of it, and is going farther into it as time goes on. But yes, this is "original work". Finding a reference for this might be difficult. Tfr000 (talk) 19:35, 29 June 2012 (UTC)
I must have done something wrong... I just don't see how this is possible. Regardless of the orientation of the Earth (and RA/dec) due to precession, the ecliptic just does not move that much relative to the stars (and hence, relative to the constellation boundaries).
Ok, got it - I was plotting everything in 1875 coordinates, and I neglected to precess the modern ecliptic to its place on the 1875 coordinate grid. At no time from 1875 to 2100 does the ecliptic come closer to the corner of Cetus than about 0°.15 (about 500 arcseconds), so the Sun is never in Cetus. Even if nutation was applicable, its amplitude is only about 9-10 arcseconds. Again, this is "original work", so I need a reference. Tfr000 (talk) 21:01, 29 June 2012 (UTC)
What I found seems to confirm Tfr000's results. I used the 1987 work of Nancy Roman cited above by Tfr000 to calculate the constellation behind the Sun for each hour in 2012 from 15 March through 22 April. The positions were astrometric positions, that is, referred to true equator and equinox of date and corrected for light-time. The calculations were done in the Multiyear Computer Interactive Almanac published by the Naval Observatory. Due to a limitation of Roman's program, I precessed them all the positions from 2012.25 to 1875.0, rather than a separate epoch for each position. The Sun never entered Cetus. It passed from Pisces to Aries on 18 April between 1600 and 1700 TT. The positions were:
Sun
Astrometric Positions
Date Time Right Ascension Declination Distance
(TT)
h m s h ° AU
2012 Apr 18 16:00:00.0 1.7871849 11.062751 1.004328442
2012 Apr 18 17:00:00.0 1.7897712 11.077205 1.004340094
I commented out the Cetus sentence for now. If we find some supporting evidence (one way or the other) we can change it if necessary. Tfr000 (talk) 12:41, 30 June 2012 (UTC)
Of course, the Sun's apparent disk is about 30" (0°.5) in diameter, so when the Sun misses the corner of Cetus by 0°.15, it covers the corner, but the center of the apparent disk never crosses Cetus. A "partial eclipse", you might say. However, it is the center of the disk, which is considered to be the position of the Sun, that defines the ecliptic. Tfr000 (talk) 12:31, 20 July 2012 (UTC)
The Sun rotates around an axis of rotation that is directed among the stars. The question is whether its north pole direction is directed at any star that we can identify within our astronomical view. It wouldn't be polaris, our north star, because of our planet's tilt away from the plane of the ecliptic. But if we knew of a star whose position was congruent with a position within the direction of the sun's axis of rotation, that should be regarded as a significant feature of the location of the star.WFPM (talk) 18:12, 31 January 2013 (UTC)
According to the Astronomical Almanac for the Year 2011 the position of the pole of the solar equator, with respect Earth's mean equator and equinox of 2011.0, was 286.15° right ascension and 63.89° declination. I don't know how stable that is or what star is near that location. Jc3s5h (talk) 20:38, 31 January 2013 (UTC)
Very Good!! Now you can see why I was wondering whether there was a star out there that I could point to and say "That star is aligned with the axis of the sun's rotation" rather than just having the knowledge of an imaginary line that I wouldn't be able to see.WFPM (talk) 21:37, 31 January 2013 (UTC) Maybe it has some angular relationship with our north pole star Arcturus. They're both on the north side of the ecliptic and couldn't be too far apart.WFPM (talk) 22:40, 31 January 2013 (UTC)
Apologies! But if there were such a star we would be better able to visually locate it in astronomical space, like we do with Polaris than imagine some imaginary line. And they would have a relationship?WFPM (talk) 17:41, 1 February 2013 (UTC)
The relevant constellation is Draco. The stars in Draco are a bit dimmer than Polaris, and none of the brighter Draco stars are nearly as close to the Sun's north pole as Polaris is to Earth's north pole (or at least, that's how it looks on my star chart). Jc3s5h (talk) 18:12, 1 February 2013 (UTC)
If you have a smartphone, there are augmented reality astronomy apps that let you point the phone at the sky and see the constellations so you wouldn't have to rely on remembering a diagram, or trying to look at it at night. TimL • talk06:29, 2 February 2013 (UTC)
If you don't have a smartphone, familiarize yourself with the star Vega, it's very easy to find as it is the 2nd brightest star in the north celestial hemisphere. Now, imagine a line between Polaris and Vega, halfway between these two stars will be very close to the north ecliptic pole. TimL • talk06:38, 2 February 2013 (UTC)
Good! Now if we create this imaginary line and put an arrow's head at the appropriate halfway distance we could say that we had created a clock hand in the heavens that would rotate (counterclockwise) around Polaris and be synchronized with the motion of the sun. I don't see what good that would do, but it would be an interesting observation. And I guess that if our view were from the north pole the hand would would be describing a circle of some angular radius that we could figure out. Is that significant?WFPM (talk) 17:21, 3 February 2013 (UTC) And when the sun is below the horizon we could say that the arrowhead (and Vega) would be pointing in the direction of the sun below the horizon>WFPM (talk) 17:33, 3 February 2013 (UTC)'
The imaginary line would have no relation to the sun as throughout the year the earth orbits the sun and the background stars change relative to our view of the sun (at a given time of night). The halfway point you describe is significant, it would be about 23.5° from polaris, which is equal to the tilt of the earth's rotation axis. The ecliptic north pole by definition has to be about 23.5° away from the north star. Also you could draw an imaginary circle that goes through vega and polaris at it widest point and that would roughly trace out the path that the north pole points to over a period of 26,000 years due to the earth's Axial precession. For further inquiry you should go to Wikipedia's Reference desk. They answer all kinds of questions. TimL • talk18:03, 3 February 2013 (UTC)
Well thank you and I wont pursue the point. I am mainly interested in starlight from stars like Vegas because I believe that the light from the star comes directly to us from the star, and accordingly the direction moves with the location of the star as we have just established. we are accordingly inundated with starlight from all the directions within the hemisphere of view when we look into the hemisphere. And therefor the light energy we get and perceive is that emitted by the star. And we're back to the process of emission and transition of light energy. You wouldn't think that this would even be a subject of debate, like it is in Talk:Energy. And the thing that impresses me are the details that we see in the Whirlpool galaxy article. You might notice in that image that when we look closely in the image (in the upper right corner) we see what looks like other more distant galaxy formations which bear testimony to the ability to travel long distances without distortion.WFPM (talk) 19:51, 3 February 2013 (UTC) But if the point of the arrow points at the direction of the sun today and tomorrow and the next day, when will it stop pointing in the direction of the sun?WFPM (talk) 23:50, 3 February 2013 (UTC) I guess you mean that we'd have to keep changing the direction of the imaginary line due to the apparent motion of Vega.WFPM (talk) 23:58, 3 February 2013 (UTC)
It would be nice with a section on accretion disc theory and for that reason a diagram like http://burro.cwru.edu/Academics/Astr221/SolarSys/ecliptic.gif that includes the angle of the Sun's rotation. It would be better with a 3D-ish drawing of course, since the planets and Sol do not all tilt about the axis through this side-on view - so as to not fool readers into thinking so. I'm having a hard time finding the right papers at the moment. The ecliptic is Earth-centric and so of less use to astrophysics, so it would be good to visualize its relation.
The comment added to the ecliptic diagram, complaining that the Earth's orientation is incorrect, is itself incorrect. As seen in the diagram, the Earth and Sun are at Summer Solstice. The Earth's northern hemisphere IS pointed toward the Sun. Remember, the ecliptic is the path of the Sun as seen from the Earth, not the other way around.
Please discuss here if this is unclear. Tfr000 (talk) 18:36, 18 January 2015 (UTC)
ε = 23° 26′ 21″.45 − 46″.815 T − 0″.0006 T2 0″.00181 T3 should .0006 be .006? 173.69.177.38 (talk) 18:10, 11 February 2015 (UTC)
compared to the equation above this one, should the coefficient of T^2 be 0.006 rather than 0.0006? It looks like a typo, since none of the other coefficients changed as much.
ε = 23° 26′ 21″.45 − 46″.815 T − 0″.0006 T2 0″.00181 T3
I disagree. An encyclopedia is supposed to be encyclopedic. The numerical value of the obliquity of the ecliptic, which is the same as the "tilt" of the Earth's axis, is fundamental to many Earth and astronomical sciences, and this is an obvious article in which to place it. We could add some stuff about why it's important, if we think it's necessary. This article is about the ecliptic, not all of that stuff, which is why that stuff is treated tersely, if at all. Tfr000 (talk) 13:03, 24 May 2015 (UTC)
Well, I removed the "overly detailed" tag. See above. The job of an encyclopedia is to present all relevant detail. The value of the obliquity is obviously extremely relevant. Tfr000 (talk) 18:56, 4 July 2015 (UTC)
Multiple problems with this article
Article distiguishes between "ecliptic", "plane of the ecliptic", and Earth's "orbital plane". Astronomers never do this. For them, ecliptic = plane of the ecliptic = Earth's orbital plane.
"Axial tilt" is never used by astronomers. It is always "obliquity of the ecliptic".
Contradictory symbols used for ecliptic latitude in section "Equator".
Most of the section "Stars" is astrological. There is little astronomical significance to the location in the constellations of the equinoxes and solistices. This should be made more obvious.
There is confusion of the concepts "true sun" and "mean sun" and what causes the difference.
"lunisolar" and "planetary precession" are used without explanation or with dubious explanation.
It is debatable whether an article on the ecliptic should contain sections on the orientation of other planets to the ecliptic - why not put that information in the articles about those planets?
The first image has a symbol Ω at one of the equinoxes. Ω is used to signify "ascending node"; by definition the Earth's orbit (and therefore the Sun's path) has no nodes. There is no perspective to clue us in to which equinox is closer to us. No explanation for why the Earth is shown at the center of the universe. Confusing.
The second image is very confusing. Pluto apperntly orbits outside the constellations. Most of the planets are bigger than the Sun. The apparent purpose, to show how the planets' orbits are oriented to the ecliptic, is not at all obvious, and would be better depicted with a side view of the ecliptic.
Lastly, no real references for all the information. One would think there should be some spherical astronomy texts.
Tfr000 (talk) 21:14, 13 March 2012 (UTC)
The use of "apparent path of the sun" causes confusions. "Apparent" to whom? If you stand on a given spot on the Earth for a year, you don't see that the Sun traces out a circle in the sky, no matter how you look at the Sun. To use the term "apparent", you must specify where the observer stands.
There are two ways to define it clearly: 1.) The ecliptic is simply the intersection of the Earth's orbit plane with the celestial sphere; 2.) Imagine that the Earth does not spin around its own axis but still moves in its orbit around the Sun as it does in reality, and imagine you, the observer, stand on a specific spot on such a non-spinning Earth for a year, you will see that the Sun traces out a circle in the celestial sphere, and this circle is the ecliptic. The best two spots for such an observation, though, are the two spots that are farthest away from the orbit plane. --Roland (talk) 06:26, 1 February 2016 (UTC)
Unfortunately, a difficult thing to describe, which is why this article and talk page goes round and round trying to define it. It would be easy to get a planetarium to show what is meant by it... other than that, we're stuck with these descriptions. But you do bring up a good point re:"apparent". I think we're describing a geocentric viewpoint, so we should probably mention something about it. The USNO says:
ecliptic:
1. The mean plane of the orbit of the Earth-Moon barycenter around the solar system barycenter. 2. The apparent path of the Sun around the celestial sphere.
Ok, we have two versions of the caption on the first graphic. It was:
The Sun seems to move against the background stars as seen from the orbiting Earth. The ecliptic is the path the Sun appears to trace through the stars. The Earth completes its orbit and the Sun traces its entire path in a little over 365 days.
and now it is changed to:
The Sun seems to move against the background stars as seen from the orbiting Earth. The ecliptic is the path the Sun appears to trace through the stars. This process repeats every time in a little over 365 days
by editor JorisvS, who claims it is against the manual of style. In the first, we know that the entire orbit and the entire path complete in 365 days. In the second, some undefined process of movement and path repeats every time in 365 days. This is a scientific/technical article, hence precision of language is important. I doubt the manual of style says we shouldn't be clear and complete. In fact, the manual of style is about appearance for the most part - things like capitalization, abbreviations, punctuation, so I, for one, am puzzled about how it applies here. Tfr000 (talk) 22:52, 13 February 2016 (UTC)
I didn't refer to the MoS for the caption, but for all the other changes you reverted alongside it. Your statement here suggests that you still haven't taken a good look at my edit and why I reverted your revert the way I did. I'm fine with discuss the caption, but I do suggest you take a good look at my edit first and look beyond the first line: here. --JorisvS (talk) 12:02, 14 February 2016 (UTC)
I probably assumed based on the byte count, sorry. If you're ok with the old caption, I will restore just that, and leave everything else alone. Tfr000 (talk) 01:17, 17 February 2016 (UTC)
Ecliptic
This page has been badly edited at some point; see toward the end the phrase "is illustrated in the following figure"; the figure no longer exists. The article badly needs a figure, words just aren't enough (picture = 10,000 words).
In an effort to respond (supposedly cleverly) to the above unsigned talk contrib, on an iPad ii (whose screen's recently -- uh --quasi-shattered screen seems to be an innocent bystander in this disastrous editing session), I may have accidentally requested deletion of some talk content that I recall having myself saved, and for the moment is not visible to me. I'm not sure I'll be able to use the edit facilities to restore (as I surely could on an internet-connected "real computer") any damage I caused to be actually saved. I shall report final outcome, and perhaps interim observations and edits on this talk page, even if perhaps in a new section within it. --Jerzy•t14:25, 8 February 2019 (UTC)
Starker contrast as to astrology needed (approximations and shape-spotting)
Without praising the progress since the Ancients too much (I hope), we do need to make it clearer that the zodiac being a "belt about 20° wide in latitude" is just the entirety of traditional star patterns (constellations) traced by the sun over the course of a year, traditionally observed just before dawn and/or after sunset, hence it varies in width to accommodate those star patterns. Just a point of view. And a critique. It was very little intended for star/space science.- Adam37Talk14:09, 9 June 2019 (UTC)
Up to the 17th century all major star catalogues and luni-solar & planetary tables were based on ecliptic coordinates as it was the reference plane for most (if not all) astronomical observations. AstroLynx (talk) 14:38, 9 June 2019 (UTC)
which might possibly do better. It would need to be redone to give English captions. I don't have graphical skills, but for any that want to fix it, here are the translations of the German captions:
b (citations to reliable sources): 
Added some text to Ecliptic#Sun.27s_apparent_motion to cover the second definition. 
b (appropriate use with suitable captions): 
