Talk:Precession (astronomy)

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    Contents

    [edit] Computer Simulations and Alternative Explanations

    The need for citations of sources has already been mentioned here so I won't harp on it. But what I want to see is studies, with actual numbers, comparing our theory of "gravitational torques" to the observed orbital motion of the earth. I know studies of Earth's orbital evolution have been done, but I've never managed to locate one. As I understand it, the numbers produced by simulation don't model the orbital evolution very well.

    An interesting theory is advocated by the people at www.binaryresearchinstitute.org . Like their name implies, they are looking for evidence that our solar system is actually a long-period binary.

    Their theory is that our sun has a small, dark companion star. The sun, and with it our solar system, orbits this companion once every 24,000 years. The object they posit could be as small of 0.06 solar masses, at a distance of 848.5AU from the sun. Pluto's aphelion is at 49.5AU. The existence of such a body is not unthinkable. And would be difficult to detect, explaining why it went unnoticed all these years. [[1]]

    This isn't the first time a dark companion star has been posited: [[2]]

    Unfortunately, the binaryresearch people might be totally insane (check out their "facts" page [[3]] ). Nonetheless their binary-orbit theory is worth investigating.

    Mseslacker 18:38, 10 February 2007 (UTC)

    [edit] Precession of The Equinox

    Here [Presession of the Equinox] is a non-technical and easy to understand explanation of the phenomenon of astronomical precession. In the least, this explanation frames the issues and the apparent effects of precession. John Charles Webb July 21st 2005

    --- The first three sentences of this article appear to be missing. --Wetman 06:20, 5 May 2006 (UTC)

    [edit] "noxes"??

    since the stem is nokt-, and the -x is the nominative singular, should't it be "equinoctes", analogous to index, indices? dab (ᛏ) 12:25, 25 May 2006 (UTC)

    You would be correct if this were the Latin Wikipedia. Ewlyahoocom 05:07, 26 May 2006 (UTC)
    Indexes is valid. ErikHaugen 17:31, 13 November 2007 (UTC)

    [edit] The Earth's precession is not due to the Sun

    I think that the Earth's precession is not due to the Sun, but it is due to the conservation of a new physical size unknown yet, which I have called volumic impulse. If the precession would have been due to the Sun, then it would take place around a line that joins the Sun to Earth, not around a perpendicularly line on the ecliptic! Even more, the precession periodicity would take place once in a year, not once in 26000 years, because at the equinox it would cancel and it would change its direction. You can find details at the address www.geocities.com/abelcavasi. I would like this discussion to be a challenge for you. Show me where I am wrong, if I am wrong. Thank you. abel 07:38, 18 June 2006 (UTC)

    I do not care what theory you have. Whether it is the sun, or volumic impulse, even gremlins would be fine. The only thing which counts is: can the theory explain all observations? And then: can it predict observations not yet done (which when done after, are in agreement with the predictions). If yes you win, you may even get a Nobel prize. If no you loose. Many people think they are Einsteins because they come with new theories. And why should they be not? Simply, because Einstein painstakely proved that all laws from nature known at that time were consistent with his theory. Better, that some with had baffled the old theories agreed with his. Therefore Abel, first show that your theory can do that too, then we will talk. Oh, and learn some mathematics and physics before you come with strange claims. Reading the explantion would also be a good idea. It is stated clearly there. The Earth is not precessing because the Sun and Moon pull on its rotation axis (then it would be as you say), but because they pull on its equatorial bulge (which has a large component nicely parallel to the ecliptic). If the Earth was a perfect sphere, there would be no precession. All right then, we put a note in. --Tauʻolunga 10:20, 20 June 2006 (UTC)
    Hi, my friend! Thanks a lot for giving me a bit of your time. I appreciate you enjoy the subject. Unfortunately, you answered superficially. Did you truly understood that the nowadays given explanation is wrong? If the explanation would be correct, then the precession should be canceled at the equinoxes, which is something unobserved. Isn't it? abel 18:01, 21 June 2006 (UTC)
    Precession seems inevitable given any orbiting body. If anything lack of precession would imply some extraneous force not known, of which there must be onus to prove. Elle vécut heureuse à jamais (Be eudaimonic!) 01:06, 24 July 2006 (UTC)
    Is this a theory that you have thought of yourself? Has this theory been mentioned in any scientific journals/magazines/books? Just curious. Bibliomaniac15 23:19, 25 July 2006 (UTC)
    Are you asking about his theory, or my sentiment? Elle vécut heureuse à jamais (Be eudaimonic!) 01:38, 27 July 2006 (UTC)

    [edit] There must be an error here

    It took me some time to puzzle this out, but something in the article didn't quite fit in. Might someone explain how there can be solar precession at equinoxes? Let's look at the picture. At solstice the sun pulls the equatorial bulge of the earth slightly harder (and vice versa, of course) than the bulge of the other side, trying to right up the tilt of the axis, which the spin of the earth converts into precession. But during equinoxes the closest and furthest parts of the bulge are on the same line to the sun, creating no difference in gravity, and the northest and southest parts are the same distance measured from the center of the sun, again creating no difference. We could argue that there is some difference since also the sun is an oblate spheroid, but in that case only the central bulge of the sun would take effect, whereas during solstice there is the whole mass of the sun causing precession. I'd estimate this effect to be, at this distance and towards the mass of a whole planet, somewhere between infinitesimal and negligible.

    The solar precession varies like a sin curve. Whenever there is precession at equinoxes, it's caused by the moon or the other planets.

    Read the article more carefully. The difference in pull magnitude at near and far side of the Earth during the solstices is NOT causing the precession (it causes the tides). The real cause is that the pull is towards the Sun (or Moon) and therefore for the tipped parts of the bulge not laying in the ecliptical plane. It has a small but existing component perpendicular to the plane. That is the term you need, which is season independent. --Tauʻolunga 20:14, 20 July 2006 (UTC)
    It is still unclear why there is torque at the equinox. The Sun sees no tipped part of the bulge then - the bulge is facing directly toward the Sun. That is, the tipping that the Sun sees *is* absolutely season dependent. ErikHaugen 00:56, 20 March 2007 (UTC)
    Also, at least some of the sources indicate that you are wrong. For example, <http://www.tenspheres.com/researches/precession.htm> says "The Sun and Moon pull harder on the nearest part of the Earth's equatorial bulge than the farthest part, and this causes a torque which precesses the Earth's rotational axis." I can see why both factors could be at play here, but it is unclear to me which is more significant. I can only note that *everything* I have seen, except your writing, Tau'olunga, indicates that it is the difference in graviational force due to the difference in distance of the two halves of the bulge that is the main factor. Do you have a source? Some calculations? It would be interesting to see a comparison. ErikHaugen 00:56, 20 March 2007 (UTC)
    Forget the ecliptical plane. There is no pull towards the ecliptical plane. There is only the gravity between the earth and the sun. The same gravity causes the tides (still ignoring the moon here) and the precession. Simple newtonian physics explain why the precession happens, namely the law of gravity; that the force of gravity is the inverse square to the distance between objects (or parts of objects here), and the law of conservation of momentum, that causes the gravitational difference to turn into precession. Read the http://mb-soft.com/public/precess.html for more info.

    Errata: I mentioned "mass of a whole planet". It makes no difference here. Sorry bout that. Also, I forgot to sign. Btw Abel, could you make an article about why we need any new laws to explain precession? It's already clearly explained.

    Heikki

    You are correct, Erik, in that the torque caused by solar precession at the equinoxes is negligible, and that precession does indeed occur faster at the solstices. It is this variance in the torque that is primarily responsible for nutation (not as the article states gravitational influence of Jupiter and Saturn. Those contribute very little to precession, either axial or anomalistic). I do not have time right now to find references, but I will endeavor to do so in the near future. Wilford Nusser 15:55, 23 October 2007 (UTC)
    I look forward to your contribution, Wilford - as far as I can tell the diagram and Tau'olunga's descriptions are incorrect, and instead, the reason for the torque is that the force on the half of the bulge furthest from the sun is smaller than the bulge on the half closest to the sun, because of the difference. I don't have sources, but I figure unsourced correct information is better than unsourced incorrect information. I'll remove the diagram, also, although a similar diagram except with correct information would be nice. ErikHaugen 19:41, 26 October 2007 (UTC)

    [edit] FA potential

    This is a highly piquing subject, and the graphics are very dramatic. We do need a lot more explanation of the effects though, and a better treatment of the matter. Elle vécut heureuse à jamais (Be eudaimonic!) 01:07, 24 July 2006 (UTC)

    [edit] I made a few mistakes!

    The picture presented Precession_torque is so well created, that, I realized with its help that I was two times wrong when I said that:

    1) The precession should change its sense of direction once at six months;
    2) The precession should be canceled at the equinoxes.

    Your picture helped me to understand that, indeed, there is always a couple that has an effect upon the Earth. But this DOES NOT MEAN that the Earth precession is explained as it is believed today and this is why:

    1) Someone said in Explanation that “It is also important to note that the torque is everywhere the same, whatever position of the Earth is in its orbit around the Sun”. I believe that this statement is wrong, because at equinoxes, the couple CANNOT BE EQUAL with the couple from the solstices because the perpendicularly component on the ecliptic IS MUCH SMALLER than the parallel component with the ecliptic. And this anomaly with the periodicity of six months SHOULD BE VISIBLE ENOUGH, but it is not experimentally observed;
    2) Taking in consideration the action made by the couple presented by you in the picture, the axes of precession should be PARALLEL WITH THE LINES OF THE SUN’S GRAVITATIONAL FIELD, not perpendicularly on it. Because any whirligig found in the Earth’s gravitational field will have the precession parallel with the Earth’s gravitational field;
    3) The precession’s sense of direction should BE THE SAME with its rotational sense of direction, because the precession of any whirligig HAS THE SAME SENSE OF DIRECTION with its rotation. This is due to the fact that the couple’s vector (which is the cross product between the precession and the kinetic moment) can be positive (as it is in your picture) ONLY IF the precession and the kinetic moment are positive. --abel 21:40, 25 July 2006 (UTC)

    [edit] Let me make this real simple

    Let us imagine a point in space. (the center of the sun's gravity) Let us imagine a bit tilted blue ring. Let us imagine four (4) vectors, two pairs of them. Pair 1: the closest and the farthest point of the ring towards the centre of the point (sun). Pair 2: from the "leftest" and "rightest" points of the ring. Let the length of the vector represent the force of gravity. the longer the vector the smaller the force. Ok? For there to be a change in the orientation of the ring relative to the point (sun). If you want to calculate the "component towards the ecliptic" it's the difference in the length of the vectors multiplied by the difference of their directions. there must be a difference in BOTH length AND direction of either pair. If either the difference of length or the difference in direction is 0, the resulting component is 0. We think only about one pair or the other, representing the x and y axis in 90 degrees angle towards each other

    Let there be solstice. Pair 1: there is a difference in both length and direction of the vectors. Pair 2: There is difference in direction, but not in length. Let there be equinox. Pair 1: there is difference in length but not in direction. Pair 2: difference in direction but not in length. Therefore, no component "towards the ecliptic", therefore no precession.

    P.S. Abel, point 3 was wrong. imagine the blue ring carefully balanced by it's center, tilted a bit, at solstice. Imagine arrows representing the straightening gravitational effect. Fasten longer arrows on the ring to the highest and lowest point, pointing downwards in the highest point and upwards in the lowest. Now rotate the ring a bit. press a little where the higher arrow (pointing down) is, and lift a little at the lower arrow (pointing up) Which way does the axis of the ring turn?

    --Hesu 20:48, 27 July 2006 (UTC)

    [edit] An error that can be observed from the figure!

    The figure Precession_torque presents us a couple with a constant direction! But it is known that THE KINETIK MOMENT OF A BODY TENDS TO GET ON THE SAME STRAIGHT LINE WITH THE DIRECTION OF THE COUPLE, just as the impulse tends to get on the same straight line with the direction of the force! Because the direction of the couple presented in the figure is constant, the rotation axis of the Earth should get on the same straight line with this direction. Then the rotation axis of the Earth should be on the same direction as the direction of the couple presented in the figure! And even if the rotation axis wouldn’t have had enough time to get on the same straight line with the direction of the couple, today we should see a precession around the direction of the presented couple. So, once again, the explanation given by the figure is wrong! Where from was this beautiful, but eronated figure brought?

    P.S.1. Bibliomaniac! The conservation law of the volumic impulse is unknown yet. The magazine in which I managed to publish a theory about this law, it's a simple magazine from Romania. The theory appears also in my web site up presented.
    P.S.2. Heikki! I wrote a more detailed article about the errors found in the nowadays explanation of the Earth's precession. This one follows to be published. I can send it to you any time you want.
    P.S.3 Hesu! I hope that these lines you will have an answer to your question. --abel 16:27, 2 August 2006 (UTC)

    [edit] The precession of the equinoxes is a great mystery!

    1). The Sun – Earth system found at equinoxes CAN’T KNOW how tilted is the Earth’s axis on the ecliptic, because the ecliptic is an imaginary plan, without any physical support! So, at equinoxes, the Earth does not have where to know from, how big the forces that produce the couple are! Does not matter how tilted is the Earth at equinoxes, the resultant couple will be null! More explicit:
    - No force can have a perpendicularly component on its self;
    - The three forces from the picture are always coplanar;
    - At equinoxes, the plan of the forces is the same as the plan of the blue ring;
    - The three forces can not produce a couple above the plan where their selves are found, because they can not have components perpendicularly on this plan.
    2). Any couple is perpendicular on the forces that cause it! If the couple that produces the Earth’s precession is due to the gravity’s forces of the Sun, then this couple must ALWAYS be perpendicular on the gravity’s forces of the Sun! So the couple from the picture will displace DOWNWARDS, not to the left side of the picture!

    You can understand now why the nowadays explanation of the Earth's precession is erroneous! The understanding of this fact is very important for Wikipedia and for Physics! Spread this news! Challenge also the other ones who you consider to be smart! Mention everywhere that the explanation of the Earth’s precession is at least contentious! --abel 05:56, 4 August 2006 (UTC)

    [edit] Torque pulsation

    I now partially agree with abel, Heikki, Hesu, Johnson (Precession of a gyroscope and precession of the Earth's axis including nutation), and Wallace (Precession and Nutation), although some of their explanations are wrong and I would use different words to describe the effect. The conclusion in the article is erroneous: "Also, the torque is everywhere the same, whatever the position of the Earth in its orbit around the Sun."

    The torque on Earth's axis is not steady but pulsates. The error in the current graphic/explanation arose because the net gravitational forces on the equatorial bulge were decomposed into components that were parallel to and perpendicular to the ecliptic. However, the torque is applied to Earth's axis, so they should be decomposed relative to that axis, both parallel to it and perpendicular to it. The bulge nearest the Sun has a slightly larger gravitational force than that on the far bulge, both at an angle to the plane of the bulges. If Earth's centrifugal force (everywhere on or in Earth the same, yet equal to but opposite the force of gravity only at the center of the Earth) is vectorially subtracted from both, and the net forces decomposed, then both far and near torques tend to decrease the tilt (tend to decrease the inclination of the equatorial bulge relative to the ecliptic). The components perpendicular to the axis are essentially equal and opposite (both pointing away from the axis) for the two halves of the bulge so they cancel. This method of decomposing the forces is confirmed in Spherical and practical astronomy as applied to geodesy by Ivan I. Mueller (New York: Frederick Unger, 1969), p 59+. (This decomposition method conflicts with that of Johnson (and Wallace), who regard the gravitational force on the far equatorial bulge at the solstices as helping to increase Earth's axial tilt while the slightly larger force on the near bulge tends to decrease it.) The components parallel to the axis create a torque which has a maximum amplitude and the same direction at both solstices. At the equinoxes the components parallel to the axis drop to zero, so no torque is applied at those times. The torque on Earth's axis due to the Moon is twice as great as the torque due to the Sun, but it also pulsates, reaching zero twice during every lunar orbit, whenever the Moon crosses the equatorial plane. Both torques should pulsate in the form of a full-wave rectified sine wave, which is electrical engineering jargon for the absolute value of a sine wave — its negative half is flipped around the zero axis and made positive.

    To comform to accepted astronomical terminology, precession itself cannot pulsate. Precession, by definition, only refers to those components of Earth's axial motion which have periods greater than 300 years. Shorter period components (from 274 years for one planetary term down to two days) are arbitrarily called nutation, not precession. Periods shorter than two days are arbitrarily assigned to polar motion.

    Nutation exhibits the pulsation. The torque on Earth's axis pulsates semi-annually and semi-monthly. The three largest nutation terms in obliquity (axial tilt) are 9.2025" in 6798.4 days (18.6 years, nodal precession), 0.5736" in 182.6 days (half year), and 0.0977" in 13.7 days (half sidereal month). The semi-monthly and semi-annual terms are obvious. The smaller magnitude of the semi-monthly term is due to the much shorter period of time during which its torque is applied — 182.6 days/13.7 days times 0.0977" produces an equivalent deflection during a half year of 1.302", which is about twice 0.5736", as expected.

    Unfortunately, to correct the explanation in the article requires new graphics, which were probably created by Tau'olunga.

    — Joe Kress 02:43, 7 August 2006 (UTC)

    I do not think that the drawing needs any change. It would be better to tell in the text that the lunisolar precession is constant, and that any seasonal variation is only a first (or maybe second ?) order effect, which is just one of the nutation terms. After all the solar seasonal effect is only 0.6" which is almost a hundred times smaller than the 50" of the precession itself. If you start to claim that the precession varies, people may go to believe that there is a swing from +50 to -50 or so, which would be a worse misunderstanding. Nevertheless any suggestion to improve on the picture is always welcome. --Tauʻolunga 03:18, 8 August 2006 (UTC)
    "The magnitude of the torque from the sun (or the moon) varies with the gravitational object's alignment with the earth's spin axis and approaches zero when it is orthogonal." Is this wrong? ErikHaugen 19:13, 19 March 2007 (UTC)
    No, this is correct - please see below under the heading, "Sun's Effect at the Equinoxes" --TomNicholson 14:13, 20 September 2007 (UTC)

    [edit] The real explanation for the precession of the equinoxes!

    Here I am trying to formulate shortly what I have detailed in the article found at the address mentioned upper:

    - Imagine two material points with equal masses bounded through a field (gravitational one) that rotates in vacuum around an axes perpendicular to the straight line that bind them. The rotation axis is passing through the system’s center of the mass. The system is considered in equilibrium, so the centrifugal force equalizes the attraction one;
    - the two material points HAVE THE IMPULSE VARIABLE, even though the movement can continue non stop due to the conservation of the kinetic moment of the system, so due to the inertness;
    - The same, we can imagine a system made from two parts „bound” through something that allows them to have THE KINETIC MOMENT VARIABLE, but the volumic impulse constant. SUCH A SYSTEM IS THE EARTH! It is formed from two parts (the earth shell and its nucleus) „bound” through a field (magnetically)! The Earth’s volumic impulse remains constant due to the inertia, while the kinetic moments of the two bounded component parts varying!

    More explicit I don’t think I could be, unless with your help. --abel 17:50, 11 August 2006 (UTC)

    [edit] Saturn’s precession is faster!

    Recently, I’ve studied on wiki the thither planet’s precession and I found out that, for example, Saturn has the period of the precession’s movement of 29.5 years. How comes? Eventhough the planet is beamier (so the necessary torque for the precession is bigger) and more thither from the Sun (so the gravity’s forces are smaller), the precession is faster. You still believe that the precession’s explanation given nowadays is correct? From my explanation results that the Moon has no magnetic field because has no nucleus and results also, that the Saturn has a magnetic field stronger that the Earth. --abel 13:13, 15 August 2006 (UTC)

    You are obviously mis-informed. The 29.5 years that you mention is the orbital period of Saturn, what makes you believe that it is also the period of precession of its rotation axis? The pole of the rotation axis of Saturn has, according to the Explanatory Supplement to the Astronomical Almanac, a motion of -0.036 deg/cy in right ascension and -0.004 deg/cy in declination w.r.t. the fixed coordinate system of epoch 2000; combined about -0.0057 deg/cy along a great circle: so the precession period is 6.3 million years. Abel, your comments and speculations on this page are totally uninsightful. You are obviously way out of your area of competence. Apparently you have nothing to contribute to the encyclopedia pages of this subject. Please stay out and do not waste our writings nor our time. Tom Peters 18:22, 15 August 2006 (UTC)
    Dear Tom, you're right. From my mistake I have made confusion between Saturn’s period of precession and its period of revolution. Thank you very much for this expostulation. I would like to say a lot of things about Earth's and Saturn's precession (about the value you provided me, the precession of Earth on the Saturn orbit, about the precession of a gaseous body) but, following your indications and because of the other's silent, I think I can not abuse any more this holy place (which “has not my contribution”). Again, thanks: you have stopped me at right time.--abel 16:43, 22 August 2006 (UTC)

    [edit] Merge

    Can we merge this article with [[4]]

    Precession cannot be merged with this article because that article discusses precession as a general mechanical concept. However, I am redirecting the capitalized name of this article, Precession of the Equinoxes, here. — Joe Kress 10:43, 2 September 2006 (UTC)

    [edit] Climatic Effects

    I may be a bit confused here, but the section in this article about the climatic effects does not seem to be referring to the precession of the equinoxes. From the first line of the article, "The precession of the equinoxes refers to the precession of Earth's axis of rotation with respect to inertial space." The axial precessions that the section mentions are not about the earth's axis of rotation but about the earth's orbital axis.

    Marbie 21:54, 14 September 2006 (UTC)
    The ice age article says "It is widely believed that ice sheets advance when summers become too cool to melt all of the accumulated snowfall from the previous winter." - When the Earth's axis is tilted one way wrt to the eccentricity of the orbit, the summers and winters are likely to be more mild on average. So some think that precession influences climate, at least some amount. ErikHaugen 22:26, 29 October 2007 (UTC)

    [edit] How would be...?

    How would be the Earth's precession if the planet would rotate in a perpendicularly plane of the ecliptic (for example, in a plane that contains the equinoxes line, or in a plane that contains the solstices line)? Happy new year!--Abel 04:28, 22 January 2007 (UTC)

    Well, the aequinoxes by definition are on the line of intersection between the aequatorial and ecliptic planes, so the solstice points can never be on the aequator. If the Earth's rotation axis would lie in its orbital plane (the ecliptic), so the aequatorial plane would be at right angles to the ecliptic, then I think there would be no precession; similarly if the aequatorial and ecliptic planes would be parallel. Tom Peters 12:37, 22 January 2007 (UTC)
    Indeed Tom, it would be like this, if the rotation I'm talking about would be the Earth's rotation around it's axis. But I forgot to mention that I'm referring about the Earth's rotation around the Sun, not around it's axis. Thanks for the answer.--Abel 09:17, 23 January 2007 (UTC)
    The movement of the Earth around the Sun is called its revolution, not rotation. You appear to ask what if the plane of Earth's revolution around the Sun (called the ecliptic plane) were perpendicular to the original ecliptic. However, you did not specify what is the orientation of Earth's equatorial plane (perpendicular to Earth's own rotation axis) relative to the new ecliptic nor did you specify what is the orientation of the plane of the lunar orbit relative to either. I assume that you want to keep the distances of the Sun and Moon from the Earth the same. Their present distances cause that part of precession due to the Moon to be twice the portion that is due to the Sun. In both cases, it is the angle between the new ecliptic and the new equatorial plane which determines the precession due to the Sun and likewise the angle between the plane of the new lunar orbit and the new equatorial plane which determines that portion of precession due to the Moon. In addition, the Sun causes the plane of the Moon's orbit to also precess around Earth's axis of rotation, which on average causes the gravitational force of the Moon on the Earth to be in the same plane as the new ecliptic—at least if the angle between the plane of the lunar orbit and the ecliptic is small. If they were nearly perpendicular, they should be independent. To summarize, it's complicated! — Joe Kress 19:26, 24 January 2007 (UTC)

    Very qualified answers, rigorous and complete! Anyway, it's interesting the fact that Newton "explained" the Earth's precession without needing the Moon (because he did not know about the nutation). Therefore, from Newton's point of view, how would the Earth precess if he would execute one revolutional movement on a perpendicularly plan on the ecliptic (and would maintain the same tilt of the axis)? --Abel 22:14, 26 January 2007 (UTC)

    [edit] Changing pole stars, Polar shift and equinoxes shift and Pole star

    There seems to be quite a bit of redundant material in these three places. The "Changing pole stars" section discusses which stars are, will be or have been best suited as pole stars. This should probably be merged into the Pole star article. I'm not going to be bold here just yet, though.

    The Polar shift and equinoxes section is relevant here. I'll try to consolidate it a bit with the last paragraph of the previous section -Dmh 17:24, 31 January 2007 (UTC)

    [edit] Copyright Vio?

    This article was largely copied from here. Isn't that a copyright vio? --172.129.133.45 06:46, 9 February 2007 (UTC)

    No. Crystalinks copies many of their articles from Wikipedia. This Wikipedia article was changed substantially in June 2006 by Tauʻolunga, which the present Crystalinks article reflects. The latest Crystalinks version in the Internet Archive (Wayback Machine), dated April 27, 2006, is completely different from the Wikipedia version, then or now, making it unlikely that Crystalinks made a substantial change during the intervening month of May 2006. — Joe Kress 06:30, 10 February 2007 (UTC)

    [edit] There must be a formula!

    In the section Explanation it is necessarily to be added a formula which proves the right value of the precession and nutation. This formula should fulfill the following obligatory conditions:

    1. it should depend on the gravitational forces of the Sun and the Moon on the Earth;
    2. it should depend on the Earth’s flattening and on its orbital revolution’s speed;
    3. it should have a vectorial character, in order to allow us the determination of the precession’s direction, too;
    4. it should be applicable for all the bodies in the solar system and even for a gyroscope found on the Earth’s surface.

    Well, does anyone know where we could find the right formula which fulfills these conditions? I’m sure there’s nobody! Since this formula doesn’t exist, can we still say that the Earth’s precession was explained? No way!--Abel 12:13, 20 March 2007 (UTC)

    G.Boué & J.Laskar, "Precession of a planet with a satellite", Icarus 185 (2006) pp.312..330 : [5]. Now finally shut up, will you? Tom Peters 17:14, 20 March 2007 (UTC)
    He won't if he doesn't have a subscription. Can someone tell us what that article says? I don't share Abel's skepticism of this well understood phenomena, but it would still be nice to see the formula. ErikHaugen 17:59, 20 March 2007 (UTC)
    As most works of publicly paid science, it is copyrighted by a commercial enterprise, and I am not allowed to make the PDF available on Wikipedia. Go to the library of a university that has an astronomy faculty: they probably will have a subscription and you can get a copy. The article is 19 pages and has 163 equations (not counting those in the appendices), so I am not going to repeat all that. Or just read any book on celestial mechanics for a more approximate treatment. Anyway, deliver us from Abel's misguided allegations! Tom Peters 20:46, 20 March 2007 (UTC)
    I don't think anyone is asking for the PDF, just a formula describing the force on an oblate object in terms of the different factors. It sounds like you're saying there is no formula in that paper that would be appropriate for the wp article? If so that's too bad, but thanks for your note. ErikHaugen 21:11, 20 March 2007 (UTC)
    <Sigh>. As R.M.Green says in his "Spherical Astronomy" (1985 Ch.9.8 p.225) "The dynamical theory of precession and nutation is extremely complex and far beyond the scope of this book". If you look around you will find many expressions in various grades of approximation, from derivation of (more or less complex) differential equations to phenomenological numerical expressions. The recent paper of Boué and Laskar seems to be the most thorough and general treatment thusfar. What would be appropriate for Wikipedia? Not too mathematical I suppose, the qualitative description should satisfy most readers. Abel however seeems to be on some crusade against established theory, apparently because he does not understand the physics and mathematical descriptions, and then believes that no-one really understands. Tom Peters 01:04, 21 March 2007 (UTC)
    Sure, the whole thing is quite complicated, but would just the force of, say, the Sun as a point source on some approximation of the Earth be too complicated? I'm not even talking about nutation. Perhaps you're right and it's not appropriate, too much math for a wp article. I'd be interested, because I'm trying to understand if the Sun exerts the force when the Earth is at the equinox (I don't see how it could). The article is contradictory wrt this question. It also contradicts its sources regarding whether the precession is mainly caused by gravity being stronger on the near bulge vs. the far bulge because the near bulge is closer. There's also a lot of contradictory chatter on this talk page, and no authoritative sources are used, at least that I can find, sorry if I'm blind here. ErikHaugen 05:56, 21 March 2007 (UTC)
    re. misguided allegations, is there a convention about deleting bizarre off topic sections of a talk page, short of archiving the entire page? ErikHaugen 21:12, 20 March 2007 (UTC)

    [edit] Precession not circular

    George Lovi, "Rambling through June Skies", Sky & Telescope 57 (1979), 558 & 564, cites P. I. Popov et al., Astronomiya, to show that precession does not cause the earth's rotational poles to make a closed circle against the background of stars, but a continuing spiral. For example, tau Hercules was almost on the north celestial pole about -7500, but will be some distance from it about 18,000. This is caused by the motion of the ecliptic, I believe.

    67.72.98.86 00:59, 26 April 2007 (UTC)Don Etz

    [edit] T or t in formulas?

    In both Explanatory Supplement 1992 (p 104) and Hilton et al. (p 356), lower case t is used for time (in centuries) in formulas for accumulated precession. In ES92, upper case T is used in the formula for the rate of precession. Should the article follow this practice?

    67.72.98.86 01:05, 26 April 2007 (UTC)Don Etz

    [edit] The ancient Egyptians and precession

    It seems likely that the ancient Egyptians were aware that the positions of the stars were slowly changing, changes that we know are caused by precession. In "This Restless Globe" (www.astrosociety.org/education/publications/tnl/45/global1.html), I note that the Egyptian Book of Day and Night speaks of binding the Leg (Ursa Major) to mooring posts, as though seeking to keep it from moving farther from the pole. However, I'm not sure it's useful to emphasize some of the more speculative ideas currently abroad about ancient Egyptian astronomical concepts and knowledge.

    67.72.98.86 01:15, 26 April 2007 (UTC)Don Etz

    [edit] Indian precession and trepidation

    Both precession and trepidation are mentioned in Indian astronomical texts according to David Pingree, Precession and trepidation in Indian astronomy before A.D. 1200 (two pages of footnotes are missing). However, both are ascribed by those same texts to Greek sources, hence did not originate in the Surya Siddhanta or some other Indian text. Therefore some mention of them is warranted in this article, as well as the article on trepidation, but with less extravagant claims.

    Hipparchus' use of lunar eclipses does not mean he used the Metonic cycle. The spacing between his eclipses, Babylonian and Hipparchan, was hundreds of years. This period could not have been a multiple of the Metonic cycle (the synodic month) because eclipses must include lunar nodes (the draconic month). Furthermore, Hipparchus used eclipses with similar appearances, requiring the use of the anomalistic month as well. Thus the saros is the smallest usable period. Both the tropical year and the sidereal year are excluded by eclipse cycles. — Joe Kress 21:18, 2 July 2007 (UTC)

    Who is making Extravagant Claims? : To Joe Kress and all others:

    Your reference to "...with less extravagant claims" in the passage above is certainly directed against my contribution in Surya Siddhanta, which DAB deleted and declared to be pseudoscience, OR, etc. A editor The way, the truth, and the light followed DAB's example and deleted everything contributed by me in precession (astronomy). Abecedare also levelled same charges upon me . I did not want to refute the wrong allegations levelled by DAB on me, because I knew DAB is a good editor and works hard without any payment for improving many Wiki articles. But he has started a chain reaction against me, which I must either refute now, or leave Wiki for ever. I have posted my refutation in the talk page of Hinduism under a heading "Clarification by User:Vinay Jha", which you must read. I never made any extravagant claim anywhere. My only mistake was that I had added a long contribution to Surya Siddhanta which was growing out of proportions ; hence I stopped adding anything to it on July 7, 2007, and started revising it is Ms-Word, together with adding authentic references which were left out in first round of composing. But before I could finish, DAB intervened three days later and portrayed me as an irresponsible guy, without realising that he was himself making 83 times more extravagant and unfounded claims in that article which I tried to rectify. All my statements were correct and fully verifiable, but DAB refused to even discuss the issue for many days, unless I compelled him to discuss it. Then, instead of discussing it in a proper way, he levelled wrong charges upon me, which must have resulted in an edit war of a newcomer against a team of administrators. I, therefore, avoided a clash with him, but my avoidance gave a wrong impression about me to other editors. Now at least three or four editors (not you) are tracking me everywhere and deleting almost evrything contributed by me. DAB is the most rational of them, and he has even started collaboration with me at least in one article started by him(Brahmarishi). Before July 31, 2007 I was busy in an international scientific conference, but now I have plenty of time to supply requisite sources to all previous contributions made by me but deleted by others. I request you to read "Clarification by User:Vinay Jha" in Hinduism which may change your current attitude towards me as an irresponsible guy making extravagant claims. All the charges made against me were wrong, excepting one : I had indeed made some statements without proper sources, but I possess authentic sources for all such statements,which now I have leisure to supply, but some Wiki editors have developed an undue bias against me which may soon force me to get out of Wiki. That is why I am not editing Surya Siddhanta although DAB had asked me to 'edit it in a responsible way", which implied that he still thinks me to be an irresponsible person. -Vinay Jha 06:21, 31 July 2007 (UTC)
    To Joe Kress : I have valuable matter concerning Surya Siddhanta, trepidation, Hinduism and related articles. Moreover, I can supply the datailed formula of derivation of precession in a short para, but I anticipate wholesale deletion of all my contribution by The way, the truth, and the light ; he describes my contributions to be "garbage by the Surya Siddhantic guy". The fact is that he himself is not interested in understanding the modern formula of precession which I had just started to contribute in precession (astronomy),but he mistook it to be Surya Siddhantic and therefore deleted it. I am again going to add it in a more explicit and sourced way, and I request you to save it from deletion because it is being demanded by many readers, including perhaps you. I had mentioned the name of most authenthentic modern source to The way, the truth, and the light,but he is not interested in first hand reading and still says that I was adding useless items. -Vinay Jha 06:45, 31 July 2007 (UTC)
    To Joe Kress : I still differ from you on the issue of value of Metonic Year, which has been rounded to 6940/19 by later sources but was actually based on more precise Babylonian sources.These ancient sources are mostly lost, and therefore I cannot refute the modern viewpoint which you mention. But one thing is certain : ancient sources say that Chaldeans could predict astronomical events more precisely than early Greeks, and therefore it suggests that the Chaldean counterpart of Metonic Year was certainly more precise. Rounded off value of Metonic Year gives a value of sidereal year which is perhaps the most imprecise among all ancient values, and could not be based upon more accurate Chaldean value from which Meton is supposed to have got his concept.I hoped you will mention this contradiction in the value of Metonic Year but you ignored my suggestions. -Vinay Jha 07:01, 31 July 2007 (UTC)
    To Joe Kress : Earlist reference to trepidation in Greece in attributed to 4th century CE (cf Wiki article trepidation), and European as well as American scholars have put Surya Siddhanta in the same period. It is therefore an extravagant claim that Surya Siddhantic value of trepidation (27°)was derived from Greek sources(8°).This claim does not explain why 8° became 27°. When you will read my contribution, you will find some proof to the contrary, but before declaring my contribution to be extravagant, I request you to discuss it in talk page of trepidation. Trepidation is a highly complicated issue in India, which baffles all modern scholars, all of whom regard it to be an error by ancients, but even today most of tradititional Indian astrologers refuse to give it up. I think this issue ought to be discussed somewhere, for instance in articles related to either astrology, or to trepidation/precession. The Wiki article on Indian Astrology (Jyotisa) is heavily tilted against traditional Indian astrology which is still compulsory in all sanskrit universities of India and also forms the basis of a large majority of almanacs used by Hindus. None of the sources cited in Jyotisa have any knowledge of traditional formulae of making true planets, and instead of trying to examine the pros and cons of traditional astrology all the authors cited there are REVISING Indian astrology more or less on European pattern. But these authors are followed only by those persons who have not studied traditional Indian systems and regard everything traditional to be wrong and unfit for examination. They forget that most Hindus still follow traditional almanacs and therefore traditional systems need to be studied even if they are wrong, for the sake of historical value. The sad fact is that even a knowledge of traditional formulae is vanishing fast.The Wiki article Jyotisa is heavily biased against traditional Indian systems and needs to be thorough revised. But I do not want to waste my time in edit wars with persons who want to impose modern astronomy on Indian astrology and do not want to elucidate traditional systems in a neutral manner. Many statements and sources in that article are false. Astrology is distinct from astronomy and the article should be informative without taking sides. -Vinay Jha 07:21, 31 July 2007 (UTC)

    History : Precession versus TREPIDATION : Joe Kress mentioned in this talk page on July2, 2007 that David Pingree had mentioned precession in Indian astronomy before 1200 AD, and Joe Kress also said "some mention of them is warranted in this article, as well as the article on trepidation". But on July 13, 2007 The way, the truth, and the lightdeleted my reference to trepidation in this article, and said "The stuff about trepidation needs a source; I've never heard of it." Joe Kress had already mentioned a major source of reference which The way, the truth, and the light ignored to consult. I was then busy in preparations for an international conference on monsoons organised by Indian Institute of Science and had therefore no time to give details and references. The way, the truth, and the light could have asked about the references, or added the tag 'citation needed'. Deleting and reverting is the last step. The historical linkage of this phenomenon with the ancient concept of trepidation needs to be mentioned, as suggested by Joe Kress. I can give proper references , but I anticipate instant deletion of all my contributions by The way, the truth, and the light . -Vinay Jha 07:53, 31 July 2007 (UTC)

    [edit] Derivation of precession formula

    The equations for derivation of precessional period are lengthy and complicated, as mentioned by Tom Peters in talk page. But if minor terms are ignored, principal components can be summarily explained in this article in easy language. This explanation is not unnecessary as The way, the truth, and the light mentioned in his message on my talk page, but indespensable because many readers are already demanding it. The most important component of Earth's precession is due to Moon due to greater torque of the Moon, which has a periodicity of slightly less than 38000 years, followed by that of Sun having a period of less than 80400 years. Both these terms are mutually related harmonically, which gives a resultant lunisolar precession of about 26000 years. Taking into account other effects, the final term is one full circle in 25771.5 years or 50.2881" per years. The relativistic component has a value of 0.035" per year, substracting which we have a value of 25789.5 years for the period of Newtonian precession. This Newtonian precession can be summarised as a harmonic product of two components : (1/25789.5) = (1/80356.7) + (1/37978.1) . These two components can be explained through simple equations involving tropical and sidereal years, synodic month and modern version of Metonic year. I had added this simple equation in the section 'Explanation' which The way, the truth, and the light deleted even without discussing it, adding an insulting reference to my contribution as "garbage" ! He wrongly imagined this equation to be Surya Siddhantic, because he did not know the value of major components of modern formula of precession which I had given.

    Another way is a detailed discussion of Newtonian and Einstein's equations. I want to add a new section in this article 'Derivation of Precession Formula' , in which this detailed method can be explained in a single short para with links to authentic websites and references. If one extra page can be afforded in Wiki, the detailed Newtonian method of deduction of period of precession due to Sun (as an example of elucidation of gravitational formula of precession) can be explained in full. But the problem is that The way, the truth, and the light is not interested in these equations and has resolved to delete everything added by me without even trying to discuss it. He deletes even my clarifications posted to his talk page, but does not delete his abusing language aimed at me. If he is not interested in learning the physics of precession, other Wiki readers cannot be forced to follow him, because many of them have already demanded a better explanation of precession formulae. -Vinay Jha 06:10, 31 July 2007 (UTC)

    [edit] Sun's Effect at the Equinoxes

    There appears to be a small discrepancy between the explanation given in the text and that shown by the diagram.

    In the text (Section 7: "Explanation") it is noted that

    The magnitude of the torque from the sun (or the moon) varies with the gravitational object's alignment with the earth's spin axis and approaches zero when it is orthogonal.

    That is, in the case of the sun, the torque approaches zero at the equinoxes. (This is clear if we consider the symmetry of the earth-sun arrangement at an equinox). However, the otherwise excellent diagram (Precession_torque.jpg) erroneously shows a torque being exerted at the equinoxes.

    Yes, the cyan arrows show real components perpendicular to the ecliptic plane which appear at first glance to create a torque, but if we consider the components parallel to the ecliptic plane (not shown on the diagram) then we see that these provide an opposite torque. The net torque, as stated in the text, is zero. This is clearly the case if instead we use a frame of reference based on the equator rather than the ecliptic: the forces on the bulge then clearly have no component outside the plane of the equator and so no torque is generated. --TomNicholson 12:49, 20 September 2007 (UTC)

    [edit] 12 constellations of the Ecliptic

    The article states that during one "Platonic" year, "the equinox regresses a full 360° through all twelve constellations of the zodiac". To be more factual, shouldn't this be "through all thirteen constellations of the zodiac"? In astrology there exists 12 constellations in the zodiac, whereas in modern astronomy 13 are recognized, of which the Ophiucus is among the largest, yet still mostly unknown to the public. —Preceding unsigned comment added by 62.165.191.149 (talk) 07:51, 14 October 2007 (UTC)

    [edit] Include orbital Precession

    If this is supposed to be an astronomical discussion of precession, then it should also include precession of orbits (and the relativistic implications), not just precession of equinoxes.

    A brief description is in the article Precession in its section Precession#Of_planetary_orbits. Seldenball 16:26, 28 October 2007 (UTC)

    [edit] Percentages Sun/Moon

    "Sun (3%) and the Moon (97%)" - does anyone have a citation for this? I reverted it, because I suspect that it isn't true, but if it is please add it back. ErikHaugen 17:37, 13 November 2007 (UTC)

    [edit] Values

    The introduction states 25,765 years for the rate of precession. Under Values, the number 25,772 is mentioned, while I'm reading a third value (25,789.5) above in 'Derivation of precession formula' by Vinay Jha. What's the correct value? -- Petersburg (talk) 21:13, 16 November 2007 (UTC)