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Contents 1 Definition 2 disputed reversion 3 reason for movement 4 geometry of the ecliptic 5 answers 6 first point of aries 7 older comments 7.1 astronomy and astrology 7.2 I smell plagiarism, Section "Ecliptic and Sun" 7.3 Ecliptic and planets

[edit] Definition

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.

[edit] 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. --Tauʻolunga 20:35, 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. --Tauʻolunga 08:17, 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)

[edit] 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. --Tauʻolunga 06:40, 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. AikBkj 18:37, 27 October 2007 (UTC)

[edit] geometry of the ecliptic

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. Danielcohn 05:13, 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. --Tauʻolunga 06:48, 1 July 2006 (UTC)

[edit] answers

Re questions: yes, the earth moving in its orbit creates the apparent motion of the Sun against the stars. The ecliptic plane contains (roughly speaking) the orbits of most of the major planets, including the earth's. (Pluto being the most obvious exception.)

Something else that you can see by "speeding things up" in a decent astronomy program; the apparent path of the ecliptic in the sky (and hence of the planets "travelling" it) rises beginning on Dec. 22 (winter solstice) and falls beginning on June 22 (summer solstice). It also "rocks" back and forth. I recommend looking at a decent astronomy program (there are some good freeware ones) to see and understand these relationships better. -- Twang Mar 3, 2006

[edit] 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. --Tauʻolunga 07:10, 1 July 2006 (UTC)

[edit] older comments

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).

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[edit] 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. Joriki 06:10, 4 July 2006 (UTC)

[edit] I smell plagiarism, Section "Ecliptic and Sun"

See the comment "(as from the list in the previous chapter)" (italics added) from the section on "Ecliptic and Sun."
Either somebody copy-pasted something, or else somebody misnomed a "section" as a "chapter."
Worrisome.

[edit] 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)