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The astronomical formulas I have seen appear to be based on working back from known observational data (e.g., the earth's precession around the Ecliptic Pole, the Anomalous Precession period, the Lunisolar Precession period, Apsidal (Perihelion) Precession and the "Mercury Question", etc.).
Is there an actual standard formula that exists to calculate precession? Specifically, one that allows the user to enter applicable values (mass of the bodies, distance, orbital period, rotation period, obliquity, etc.), and come up with the precession value? Such a formula should work with any given value (including values given for any hypotheical planetary system).
Unless such a formula exists in the scientific community, I tend to agree with those who hint that determining Precession remains an open-ended mystery (at least regarding both its cause and its affect outside calculations based on direct observation).
Granted, any standard formula would only be accurate to so-many decimal places (due to not being able to account for ALL the multitude of minor gravitational influences from lesser bodies throughout any given system and beyond). Nevertheless, if science has determined the true cause and affect of precession, then a standarized formula (with known-body input values)should exist. Otherwise, any questioning mind may be justified in questioning the existing theories.
The many with greater knowledge may know of such a formula. If so, may it be included on the Wiki page? Oh ... and it would be super if it was written in a manner that is can be interpreted by mathematically limited individuals (who, me?!). -- Tesseract501 06:10, 12 October 2008 (UTC)
Yes, there are many precession nutation models, the most comprehensive is the 2000A model with almost 1400 terms. The problem is the models are "not consistent with dynamical theory" according to the International Astronomical Union (IAU 2006 P03). Also, while the models find a value close to the observed rate they have been unable to predict "changes" in the precession rate (such as the constant increase in the rate over the last few hundred years). Consequently, the models are revised or modified every few years to better match precession observations. This has been going on since d'Alembert substantially modified Newton's formula which did not work. Of course the changes keep getting smaller but one has to wonder if many of the unknown dynamic assumptions (concerning the shape and viscosity of the earth's core, etc.) are included to make the model fit the observable. Interesting area of study. —Preceding unsigned comment added by 69.234.46.179 ( talk) 21:33, 16 November 2009 (UTC)
The section referring to precession of the equator should be deleted ASAp unless a reference supporting the assertion that `precession of the equinoxes' has been replaced by 'precession of the equator' Terry MacKinnell ( talk) 22:52, 27 February 2009 (UTC)
It's not very clear who these 'pre-modern' astronomers are supposed to have been, who called it the 'precession of the equinoxes'. Plenty of sources show that up to about the end of the sixteenth century AD, which is pre-modern if you like, it was often called 'the motion of the eighth sphere' (e.g. 'De motu octavae sphaerae', I.Werner, Nuremberg, 1522). 'Precession of the equinoxes' is a _relatively_ modern term.
It's also not very clear that the term 'precession of the equinoxes is out of date, either. It's not equal to either the 'precession of the equator' or the 'precession of the ecliptic' -- it's the combined effect of the two of them together. Is there a replacement terminology for that? —Preceding unsigned comment added by 86.14.225.140 ( talk) 18:15, 1 March 2009 (UTC)
Isn't the direction of the precession wrong in the picture? The angular momenta is supposed to be conserved and thus the precession must be in the same direction as the body is spining. Besides I actually found another copy of the same image on the internet with the correct direction of the precession.
Samuel —Preceding unsigned comment added by 83.250.175.92 ( talk) 22:23, 5 March 2009 (UTC)
No! Precession is in the opposite direction to the spin - otherwise it would be called PROcession of the equinoxes! TomNicholson ( talk) 15:33, 18 November 2009 (UTC)
If the Earth's axis of rotation is orthogonally projected to the plane of the solar system, is the projected direction parallel to the major axis of the orbit? If so, is there an explanation of such a phenomenon in gravitational terms? 132.70.50.117 ( talk) 10:23, 5 May 2009 (UTC)
When does the current precession cycle finishes? Echofloripa ( talk) 23:14, 16 July 2009 (UTC)
Zbayz changed the name of this article from "Precession (astronomy)" to "Axial precession (astronomy)" without any discussion whatsoever. His stated reason was "This article only discusses precession of the rotational axis. It says nothing about perhelion precession." both of which are wrong. Although the dominant focus of the article is 'axial precession' it does mention "planetary precession" now renamed "precession of the ecliptic" and "anomalistic precession". The proper name for 'axial precession' is either the old name "lunisolar precession" which was used for at least two centuries or its new name, since 2006, "precession of the equator". Furthermore, this article mentions "planetary precession" now renamed "precession of the ecliptic" which is the gradual change in the inclination of Earth's orbit relative to the invariable plane of the solar system and the combination of "precession of the equator" and "precession of the ecliptic" which is called "general precession" and has been so named for at least one and a half centuries. This article also has a section on "anomalistic precession" at the end of the article, which Zbayz calls "perihelion precession", but refers to an article named apsidal precession.
Zbayz also did not follow Wikipedia naming conventions for disambiguating articles. Do not use a parenthetical qualifier unless two or more articles have the same name. — Joe Kress ( talk) 22:42, 25 August 2009 (UTC)
I suggest to split out astronomic scientific material of this article and through out pseudoscience astrological data. There is no reasons to cover both this topics in the article. Astrology - is a cultural phenomenon, not the science. Thank you. —Preceding unsigned comment added by 95.133.136.138 ( talk) 14:14, 7 September 2009 (UTC)
Are you suggesting that science is not a cultural phenomenon? TomNicholson ( talk) 15:36, 18 November 2009 (UTC)
Astrology was (and for a long time) the reason for astronomy. I notice it has lost cultural colective favour (except in Biblical instances such as the star of Bethlehem, kings choosing when to procreate etc - where it is regarded as a part of gods plan) When you say ' through out' pseudoscience astrological data. I presume you mean - 'throw out'. This vandalism you blithely propose is just that. 188.220.186.57 ( talk) 15:29, 30 August 2011 (UTC)
From the Effects Para:
Thus, the tropical year, measuring the cycle of seasons (for example, the time from solstice to solstice, or equinox to equinox), is about 20 minutes shorter than the sidereal year, which is measured by the Sun's apparent position relative to the stars. Note that 20 minutes per year is approximately equivalent to one year per 25,771.5 years, so after one full cycle of 25,771.5 years the positions of the seasons relative to the orbit are "back where they started".
I calculate that 20 minutes per year gets 360 degrees of precession in 72 years not in 25,771.5 years. What's going on here? Who did this math? Lkoler ( talk) 04:53, 16 October 2009 (UTC)
I agree with Lkoler. Common sense indicates otherwise. 20 extra minutes per year? There are 24 hours in a day. 20 minutes is 1/72 of 24 hours. Certainly, the stars(celestial sphere) are not adjusting 1/72 every year. That would put precession at super speed and we would be cycling through the constellations every 72 years. Something is wrong in the math. Common sense just doesn't support it.
If time passes by, then the celestial sphere moves. Actually, the celestial sphere moving is the cause of the time measurement, not the other way around. So, if the celestial sphere moves 20 extra minutes from what it was the year before, it must move 1/72 of the angle of the sky. 360 degrees multiplied by 1/72 is 5 degrees of the sky every year. And (divide 5(18,000 arcseconds) degrees by 365 days)would have to move about 50 arcseconds every day. This does not happen.
Remember, an extra 20 minutes per year would mean the celestial sphere shifts 5 degrees every year, and 50 arc seconds per day. It's not 50 arc seconds per day, it's 50 arc seconds per year. Hipparchus could tell you that. It's obvious, but a lot of people are getting it wrong for some reason.-- Markblohm ( talk) 18:10, 8 December 2009 (UTC)
An extra 20 minutes causes the earth to point 5 full degrees different in relation to the stars. Just like an extra 12 hours would cause a 180 degree change. Think about it. 1 tropical year is when the sun is back to the same position in relation to the earth. A tropical year plus 12 more hours would have us facing the opposite way. Likewise, 20 extra minutes would have us facing 5 full degrees off from the previous. Say at time zero you are facing 0 degrees angle. 1 day later you are also facing 0 degrees angle. 100 days later, still 0 degrees angle. 1 tropical year later exactly, and you are facing 0 degrees angle. But what is being said is that 20 more minutes is being added to the tropical year. That is 5 full degrees extra of the celestial sphere(because we have a 24 hour day). 1 tropical year later, the sun is in the same position. The shift is 50 arcseconds of the celestial sphere/year(this shift of 50 arcseconds has been observed for a long time, and is much less than 20 minutes.-- Markblohm ( talk) 21:06, 8 December 2009 (UTC)
I now understand why the time of around 20 minutes is being found. The math is not wrong. The equation is wrong. Precession is independent of the spin of the earth, so to account for the total seconds of the spin of the earth in a year when finding the real time change of precession is incorrect. Even if we say that it is wobbling, the wobbling is occurring independent of the spin. The "wobble" is only about 50 arcseconds, and is independent of the spin of the earth. We add the extra wobble time onto the total spin at the end of the year. After all, 50 arcseconds of angle(or 3.3 seconds of real time) is the change each year, which is clear to observing astronomers in the past and present.-- Markblohm ( talk) 01:47, 9 December 2009 (UTC)
No matter what equations you throw up, 50 arcseconds can never be anything other than 3.3 seconds of real time, just as 180 degrees can never be anything but 12 hours of real time. The spinning earth arcseconds do not get factored into the precession equation. You have made the very common error.-- Markblohm ( talk) 01:58, 10 December 2009 (UTC)
It appears to me that Lkoler and Markblohm are consistently confusing two kinds of circular motion. 50 arcsec of daily rotation takes 3.3 sec "of real time", but 50 arcsec of annual revolution takes 365 times as long. But that's so obvious that someone ought to have pointed it out by now, so have I missed something? — Tamfang ( talk) 06:04, 10 December 2009 (UTC)
Ah, but we're not measuring 50 arcseconds of annual revolution. If we measure 50 arcseconds of annual revolution(earth's orbital circumference) then we do get 20 minutes. It indeed takes 20 minutes for the earth to travel 50 arcseconds of the orbital circumference. But the observed 50 arcseconds of celestial sky movement is 1/365 of that. Because the earth spins 365 times in its orbital revolution. That is what the famous 50 arcesonds is, 50 arcseconds of celestial sky displacement viewed from the earth every year, cumulative for the whole year. An ancient astronomer like Hipparchus only observed 50 arcseconds of celestial sky displacement per year. He could not have observed 50 arcseconds of the orbital circumference.-- Markblohm ( talk) 15:26, 10 December 2009 (UTC)
Hi Joe(Kress.) May I ask, why are you multiplying 50" by 365?-- Markblohm ( talk) 16:07, 10 December 2009 (UTC)
Dear Tamfang, You have highlighted the problem exactly. I assume by double rotation period you mean two times faster. But even if you mean two times slower it doesn't matter. If the earth were spinning(rotating) at double it's current speed(and precession rate remained the same), the precession rate would be exactly 3.3 seconds. The seasonal year would still be the tropical year length PLUS the 3.3 seconds. The spinning earth doesn't multiply the precession, which is what is being said in these equations above. You are multiplying the precession time by the amount of days. That is incorrect. The precession movement is independent of the spinning, so you must ADD the extra precession time onto the length of the tropical year.
The sun "travels" in the sky 473040000arcseconds(365(roughly) x 360 degrees) in one year. The celestial sky travels 473040000arcseconds PLUS 50 arcseconds. In other words, the sun travels 31536000 time seconds(525600 minutes) in one year. It then takes 3.3 seconds(50 arcseconds) to catch up on the vernal equinox. These arcseconds/time seconds have been accumulating all year. On the half year the sun would take only 3.3/2 seconds(25 arcseconds to catch up). The sun travels through the sky roughly 473040000arcseconds in one year, the celestial background is travelling 473040050arcseconds.-- Markblohm ( talk) 20:23, 10 December 2009 (UTC)
Markblohm: My equation for the annual precession time is independent of Earth's rate of rotation. If Earth rotated twice as fast, its day would be half as long, 43,200 seconds, but the number of those shorter days in a year would be twice as many, 730.5 days, so there would be no change in the precession time in a Julian year, 20.42 minutes. The angular speed of the Sun in its apparent orbit around the Earth can also be used to determine the time it takes an equinox to precess along the ecliptic in one year. The Sun moves at an average speed of (1,296,000"/yr)/(365.25 days/yr) = 3548"/day. Hence the annual precession time is (50.29"/yr)/(3548"/day) = 0.014174 day/yr = 20.4 minutes/yr. You agree that this is correct via your statement "It indeed takes 20 minutes for the earth to travel 50 arcseconds of the orbital circumference." But you then state "An ancient astronomer like Hipparchus only observed 50 arcseconds of celestial sky displacement per year. He could not have observed 50 arcseconds of the orbital circumference." To Hipparchus these were a single concept. A little history is warranted:
Hipparchus and Ptolemy regarded the Universe as the stars, five planets and the Sun and Moon all revolving around a motionless Earth at their center. The orbit of the Sun around Earth (the mirror image of Earth's orbit around the Sun) marked the ecliptic, which was also the center of the zodiac, a band which contained the orbits of the Moon and the five planets. But the dominant motion (now known to be due to Earth's own rotation) was parallel to the celestial equator, which was inclined to the ecliptic by 23.5°. Hipparchus discovered that the stars had an additional motion parallel to the ecliptic called precession. A ring mounted in the plane of the equator was used to determine the date/time of the equinoxes, which occurred when the shadow of the Sun cast by the upper part of the ring fell on its lower part, meaning that the Sun was crossing the equator from south to north or vice versa. The location of the equinoxes and solstices among the stars was determined using the Moon as an intermediary because it was visible both during the day and night.
Hipparchus determined that the ecliptic longitude of Regulus, a star within 0.4° of the ecliptic, was 295⁄6° east of the summer solstice (119.8° east of the vernal equinox) in 129 BC. Ptolemy determined that the longitude of this same star was 321⁄2° east of the summer solstice (122.5°) in AD 139, so Ptolemy noted that the star had moved 22⁄3° in 265 years (we now say the summer solstice moved, not the star). From this he concluded that precession was 1° in 100 years or 36"/yr, the same precession that Hipparchus had deduced (precession is now known to be 1° in 72 years or 50"/yr). Today (J2000), Regulus has a longitude of 150.2°, so the solstices and equinoxes have precessed 30.4°, about one zodiacal sign, in 2,129 years, a precession of 51.4"/yr (using Hipparchus' imprecise position), about the same as the modern value. Hipparchus and Ptolemy used twelve zodiacal signs of 30° each to measure longitude. Precession measurements never used or depended upon either the solar day or the sidereal day. They also determined the angular distances (called declinations) of those stars north or south of the equator. They noted that stars near the autumnal equinox which were north of the equator later moved south of the equator (south to north near vernal equinox). Both methods resulted in the same precession. This "celestial sky displacement" was along the ecliptic, which was the "orbital circumference" of the Sun's orbit.
By the 18th century, astronomers no longer needed to use ancient observations, but were able to determine precession by comparing the positions of stars determined at times less than a century apart. These modern astronomers also discovered that some stars had large proper motions ( Sirius moves about 1.3" every year), which had to be excluded from those stars used to measure precession. The pointing accuracy of the largest telescopes is now about 5", so precession is observeable within one year and must be considered to even locate stars at high magnifications if a star catalogue several years old is used.
Although you state that the spinning Earth does not multiply the precession, that is exactly what you do via "(365(roughly) x 360 degrees)". — Joe Kress ( talk) 22:35, 15 December 2009 (UTC)
This image, currently shown at the top of the page, is confusing in that the rotation of the axis is shown to be in the same direction as the spin of the planet. A reading of the description (click on the image to go to the image page and see the summary below) reveals that the axial rotation shown in this image is "relative to the direction to the Sun at perihelion and aphelion", (ie. it relates to orbital precession - even though the orbit is not shown), rather than axial precession, the title of this page. The commonly understood meaning of the unqualified term "precession" is axial precession relative to the fixed stars, where it moves counter to the spin (hence the term PREcession, rather than PROcession).
This image appears here: http://earthobservatory.nasa.gov/IOTD/view.php?id=541 with the words "orbital precession" at the top. Why have these words been removed? Is someone purposefully trying to confuse here? TomNicholson ( talk) 16:57, 18 November 2009 (UTC)
I would edit this section directly if it were not for the fact that the image has errors, and I don't have a replacement.
The vertical cyan (pale blue) arrows and the yellow arrows (shown at the equator) indicating the torque should not be present at the equinoxes - the symmetry of the earth-sun relationship at the equinoxes (and hence the lack of torque) is more clearly seen if the orbital motion (which is irrelevant) is ignored, or with reference to the first equation in the following section where it is seen that the torque vanishes at the equinoxes when delta (and sine delta) become zero. This is mentioned in the text: "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, at the equinoxes.
Is anyone else bothered by the statement, "This average torque is perpendicular to the direction in which the rotation axis is tilted away from the ecliptic pole, so that it does not change the axial tilt itself"? It is the axis of the average torque which is perpendicular to the direction in which the rotation axis is tilted away from the ecliptic pole, and I don't believe it is obvious why this does not change the axial tilt itself. Actually, the "force" of the torque tends to "want" to lessen the axial tilt - a tendency which is thwarted due to the (counter-intuitive) properties of spinning objects. If at this point you think I'm completely crazy :) then try the following ...
Take a bicycle wheel (minus the bike) and hold the spindle in your hands so that your arms are like the front forks of the bike. Spin the wheel. Now (carefully!) try and change the axis of rotation. Weird, isn't it?!
TomNicholson ( talk) 18:07, 18 November 2009 (UTC)
The Introduction mentions a period of 26,000 years and a cone of unspecified size and direction.
A cone is not necessarily circular.
I think that it would be well to indicate, in the introduction (but not necessarily in these terms), that the direction of the Earth's axis of rotation moves in a circle of radius 23.5° about the Earth's orbital axis ; and that the current direction of motion is approximately along a line from Polaris towards some other well-known star. The one which it will be near in AD 4000 might suit ; perhaps in Cepheus, probably Gamma, I think - or maybe use the Great Square.
The circularity and size are present, buried lower down.
82.163.24.100 ( talk) 14:33, 24 November 2009 (UTC)
Could someone perhaps take a look at the related Great Year article? A number of questionable edits have been made recently. The new "Confusion of the Platonic Year with Precession" section may be of particular concern. Pollinosisss ( talk) 07:20, 14 December 2009 (UTC)
In 12,850 years, will the date of the vernal equinox in the Northern Hemisphere still be March 20th or will it be October 20th? Why has the date decreased from March 22nd a century ago to March 20th now? Keraunos ( talk) 16:14, 1 January 2010 (UTC)
Thank you so much for the clarification. I had always wondered about that problem. Happy New Year 2010! Keraunos ( talk) 11:06, 2 January 2010 (UTC)
If the article is going to discuss Mithraism in detail, it might as well give a nod to "tropical astrology" vs. " sidereal astrology" and the so-called " Age of Aquarius"... AnonMoos ( talk) 13:03, 15 January 2010 (UTC)
The Articles INTRODUCTION is overly complex and therefore poorly explained .The diagrams a bewildering to none-astronomers.Is this the object of wikipedia? A celestial sphere, the sun at the centre with a zodiac ring drawn as a band on the sphere, would be a better introduction.This would: (a) Root the observations to a fairly universally known (and therefore familiar) set of coordinates. (b) Remove the visual confusion (c) Allow for a clear intersection planes to be inscribed on the sphere. I would butte in a fix it myself but its really up to those most impassioned in this debate.Anyway were does a layman get the computer program to generate the diagrams?Ha! —Preceding unsigned comment added by Chasludo ( talk • contribs) 23:55, 16 January 2010 (UTC)
I moved Cuvier's 1825 estimate (recently added by Hmschallenger) to the Middle Ages onwards section, at least temporarily. It certainly does not belong in the Hipparchus section just because it uses observations by Hipparchus. It should be in a "modern estimates" section which currently does not exist. A good start would be Evolution of adopted values for precession by Jay H. Lieske. — Joe Kress ( talk) 23:54, 24 January 2010 (UTC)
I cannot see a credit at
http://www.crystalinks.com/precession.html
to this article.
There is a simple one link on a line by itself that is labeled "wikipedia" but no indication that the article is copied. The link is not labeled "orginal wikipedia article" or the like. I cannot see that the mere label "wikipedia" constitutes either a reference or credit and the owner appears to have a commercial site (psychic this or astrological that)
In the case of
http://encycl.opentopia.com/term/Precession_of_the_equinoxes
there is a fine print credit to wikipedia without actually naming this article. —Preceding unsigned comment added by Grshiplett ( talk • contribs) 00:52, 4 March 2010 (UTC)
In the section about Mayans it states that professional scholars do not hold the opinion that the Mayans where aware of precession. The reference is written by a Mayan scholar who does hold that opinion and states her opinion uncategorically in the article by saying... "The end of the baktun on the winter solstice is not a coincidence, and this mathematical feat is certainly a sign of a sophisticated link between Maya astronomy and mathematics." Yourliver ( talk) 14:46, 11 May 2010 (UTC)
There's some dispute here about what causes precession of the equinoxes. I got rid of the picture, which I think is misleading. My edits have been largely reverted here: [3]. There is more discussion here: [4] if anyone is interested. ErikHaugen ( talk) 23:03, 14 June 2010 (UTC)
Here is the summary, as I see it: There are two competing explanations for precession of the equinoxes. At least one is totally bogus. The first considers the "vertical"(north/south) and "horizontal"(sunward) components of the forces on the halves of the bulge by the sun - the vertical components point in opposite directions and cause a torque. The second, (which I assert is right), is that the difference in magnitude, due to the difference in distance to the sun, causes a torque, since the sun pulling on the closer half of the bulge causes a torque in one direction, and the sun pulling on the far half of the bulge causes a torque in the other direction - the close half wins since the distance to the sun is closer. Note that the two explanations disagree on basic things like "At the solstice, in what direction is the torque caused by the sun pulling just on the far half of the bulge?" And also note that the first explanation does not have anything to do with the inverse square law and gravity getting weaker with the difference in distance. Please say if you do not agree with this assessment. To resolve, can we cite sources? ie, can someone suggest a particular page of a particular astronomy book? (I'd sure appreciate one that freely available online.) I'll offer:
I still think you are mistaken, and so are many others, and in fact it is very difficult to find any literature about precession which try to explain the cause. Most quickly pass this part and then directly jump to the results. There are some however:
Looking at this picture we see the vectors of the differential gravitation for different angular distances from the disturbing body. It is true that there is no tangential component whatsoever if the sun/moon are on the equator, so no precession takes place. But that does not mean that there is none at the equinoxes. Because the equatorial bulge is not a single point, it is still a whole ring. That is the crucial issue. Even if during the equinoxes the point of the bulge 'under' the sun is on the equator and not doing anything, the extreme (solstice) points are then on the terminator, and they still are subject the tidal force towards the equator. In fact it does not matter where the sun is somewhere, equinox, solstice or somewhere in between, that part of the bulge north of the equator experiences a force to the south (strongest at the northernmost part, going down to zero to the equator) and vice versa for the southern half. The two forces of course are part of a torque, and there the precession begins. It also means that the precession force is always the same, the whole year around (or the whole month around if you talk about the moon). How otherwise could the precession speed of 50" per year be a constant (ignoring secular changes and the several magnitudes smaller irregularities of the nutation) as everybody agrees ? No astronomer has ever observed that precession would come to a standstill at the equinox and reach full speed at the solstice; it just progresses at a constant rate during the year (and the month).
So the torque does not change over time. What does change on the bulge when the sun (or moon) appears to go round the ecliptic plane is the strength of the radial component, the difference being largest at the equinoxes. But a radial component does not contribute to a torque. If there is anything 'bogus' there is that.
Please restore the picture. It is still correct.
What about the quote of Kaler and others above? I am sorry, no doubt dr Kaler is an excellent astronomer, but he is specialised on stars and nebuale, and therefore less at home in celestial mechanics. His statement on variable precession is utterly wrong. -- Tauʻolunga ( talk) 08:51, 15 June 2010 (UTC)
Right now, this page redirects from Axial precession. But since there is no other type of axial precession, there doesn't appear to be a need for a qualifier at the end. Serendi pod ous 18:07, 10 April 2011 (UTC)
By consequence, the constellation is no longer visible from subtropical northern latitudes, as it was in the time of the ancient Greeks.
How are we defining 'subtropical northern latitudes' here? Because I'm at about 25N, and I can see the top half of the Southern Cross from my driveway, 'in the city', when it's a sufficiently clear night. Around March, to be specific. I imagine it's a much better view in the Keys, with the clearer horizons.
I am hesitant to revise that line without either the original justification for it referenced, or what documentation on my part would be appropriate.
Corgi ( talk) 14:28, 15 July 2011 (UTC)
What is the tilt of the precession central axis with reference to the ecliptic of the sun, seeing that tidal torque forces from the moon are stronger than the sun's tidal forces, and the moon's orbit is not aligned with the solar ecliptic, defined by earth's orbit about the sun? The precessional central axis should be on a tidal torque coordinate that is a mathematical mix between the stronger lunar orbit tidal torque, and the weaker solar ecliptic tidal torque, and as such would also shift solar and lunar positions on horizon reference points, with the precession period over the approximately 30,000 year period. With an ecliptic-reference tilted central precession axis, these precession effects would misalign the claimed thousands of year old monuments based on the precision of solar and lunar horizon reference points on claimed ancient precise stone monuments like Stonehenge, and other ancient horizon reference stone marker systems. At least hyperbole, in media claiming such monuments still have "exact" alignments, whatever the word "exact" means in media. Only monuments aligned to the earth's own axis, like The Giza Pyramids, would remain constant, of course pointing to a moving pole, as the star charts show with Polaris today, or Thuban, or Vega, at other points on the precession path. Not to mention systems of stellar alignment, like claimed Nazca Lines, pointing to Sirius and Orion, seem to be media hype, having nothing to do with the Ecliptic, and claims of ancient formation toward these alignments, which will definitely not hold over thousands of years. LoneRubberDragon 76.166.233.62 ( talk) 06:54, 5 August 2011 (UTC)
User:TomNicholson would have us believe that precession and procession are opposites, which is news to me. The two words come respectively from (the Latin ancestors of) precede, 'go before (something else)', and proceed, 'go forward'. Let's either have some support for the claim or delete the new section asserting it. — Tamfang ( talk) 21:13, 24 December 2011 (UTC)
I'm replacing a couple of the graphics with some animations - in particular, the two depicting "inside the celestial sphere" and "outside the celestial sphere". We will need to update the text immediately under them to reflect the new graphics. Tfr000 ( talk) 18:34, 9 May 2012 (UTC)
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What angle is the cone made by Earth's rotational axis in the first illustration? The article begs the question. Maybe add it to that first illustration. I'm still not sure, my best guess is 23DEG based on the article.
Pb8bije6a7b6a3w ( talk) 23:23, 27 February 2013 (UTC)
The rotation axis of the Earth describes, over a period of 25,700 years, a small circle (blue) among the stars, centered on the ecliptic north pole (the blue E) and with an angular radius of about 23.4°. Please feel free to edit the article to make this more clear, if that is what you meant. ErikHaugen ( talk | contribs) 17:42, 28 February 2013 (UTC)
I think the section called Equations is unclear. You see equations but it is not at all clear how they were derived. The reason for choosing an ecliptic plane coordinate system is unclear, An earth center fixed, non-rotating coordiante system with x and y in the equatorial plane, z along the earth polar axis positive north and with x pointing in the vernal equinox direction positive seems to be much better. The derivation in Meirovitch's "Methods of Analytic Dynamics" is much clearer in my opinion.
From the introduction: "...although evidence from cuneiform tablets suggest that his [Hipparchus'] statements and mathematics relied heavily on Babylonian astronomical materials that had existed for many centuries prior..." It'd be great to have a source for this to reference. The History material later in the article doesn't provide a source for this either. Any ideas anyone? Bob Enyart, Denver radio host at KGOV ( talk) 17:18, 29 June 2013 (UTC)
Please split topic.
This section is about precession whatis and maybe short cause with lead to other topic: the usual.
It's not a topic to cut and paste earth moon / earth body formulas (and words) from likely copyrighted books ! that MIGHT contribute to precession. MIGHT.
Please create a new topic for that. I vote: split
BTW. current theory is moon hit earth which would give it INITIAL precession. the equations are paste they assume no initial precession and do not imply whether or how precession would continue or balance if the newtonians frame forces were removed.
another concern the equations mention forces two non-parallel as contributing (didn't cancel.) HOWEVER. it said nothing about, say, 250000 (or any) yrs later when THE OPPOSITE SIDE would get the same treatment thus almost wholey cancel the unbalanced forces mentioned
the formula is there (needs many conversions to use: T). and the precession itself is bound to be constant rate and rate (like a top) and is tabled in article.
but for an easier to use formula for effect on season length, see tropic year in wikipedia it has a good equation and tables
The illustration shows the axial precession of the Earth. Looking at it it would appear to me that half way through, the Earth is tilted the opposite way from the beginning of the circle and in that case summer would be reversed (if at the beginning of a cycle, summer is June 21 - Sep 21 or so in the northern hemisphere, then half way through the cycle June 21 - Spe 21 would be winter in the northern hemisphere). I suppose that is not true but that is how it looks doesn't it?
== tc
OK. But it is true then, right, that the perihelion (now in winter) and the aphelion (now in summer) will at times be switched (perihelion in summer and aphelion in winter)? I think I got those terms right. There is also apogee. — Preceding
unsigned comment added by
63.84.231.3 (
talk)
13:08, 2 July 2014 (UTC)
The blending of art and science greatly hinders each and every scientific discipline that is contaminated. I wish there was a more gentle word, other than "contaminate," because imagination and creativity are crucial traits for a species to have, however, when the line that separates what we know from what we think, gets blurred, we eventually get flat out false assumptions accepted by the masses as truth. The precession of Astronomers and Astrophysicists from sort of right to completely wrong and then back to almost accurate observations is the only thing that occurs. And if Astronomers and Astrophysicists could be honest enough to just admit the things that we don't know with scientific certainty, so that it doesn't get confused with things we know with certainty, We wouldn't be so lost and argumentative with Our knowledge of how things work. Scientists do not debate like this, peer review does not mean hold a debate to discern the Truth. And this subject is a perfect example of the nonsense that gets accepted as fact. These subjects are why the world still, to this day, believes the Moon causes the tides of Our Oceans, or that Our Solar System is hurdling outward in a straight line which fools somehow think proves the expansion of space. The ego of men and the feeble minds which encourages arguing for one exaggerated false claim over another, and Our allowing foolish men and their false theories to be accepted as facts, has severely hindered humane beings' ability to understand this world. And that is sad. - Dirtclustit ( talk) 13:14, 21 August 2014 (UTC)
@Dirtclustit: Nice. Far too much certainty given to hypotheses in most sciences.
In the section 'equations' there is:
T = 3GM/r^3 ...
I don't see any support for that not other result, and none of references to this solution also. What this is a pseudoscience or religion? — Preceding unsigned comment added by 217.99.107.103 ( talk) 00:06, 12 December 2014 (UTC)
17:38, 28 December 2014 (UTC)17:38, 28 December 2014 (UTC) 83.26.156.68 ( talk) 17:38, 28 December 2014 (UTC)
http://adsabs.harvard.edu/abs/1994AJ....108..711W
I don't see there any derivation, just this same formulas - the final. BTW. The suppositin the potential of an oblate spheroid is responsible for a precession of the same spheroid is wrong, because the momentum can be conserved in other way, for example the orbital momentum can change accirdingly.
The method of solution and these formulas are adequate for a satelite's orbital precession of the Earth, but not for the Earth itself.
The suppositin the potential of an oblate spheroid is responsible for a precession of the same spheroid is wrong, because the momentum can be conserved in other way— Can you rephrase this? I'm not sure what you're saying. In particular, are you suggesting a change to the article? Can you be more specific about the change you'd like to see? ErikHaugen ( talk | contribs) 19:16, 30 December 2014 (UTC)
00:50, 7 January 2015 (UTC) 217.99.238.57 ( talk)
"The term (C−A)/C is Earth's dynamical ellipticity or flattening, which is adjusted to the observed precession because Earth's internal structure is not known with sufficient detail."
So, it's rather evident it's just a manipulation of numbers, not any real solution.
What is a precession speed of a massive ring or disk inclined at angle i, and spinning with speed w?
No valid observation has been made across 26,000 years yet. It is unproven, so the title of the article must be presented as an experiment in vitro. All information should be re-evaluated in this regard. The article must be changed to "Axial Precession Theory", as written in heading of this new section. — Preceding unsigned comment added by 72.94.152.209 ( talk) 12:18, 26 February 2015 (UTC)
It seems to me very questionable if the section "Mithraic question" belongs here at the present length, or at all. At least most of it is wholly outside the topic. It is not even known whether Mithraic Mysteries had anything to do with the precession at all; it is just the wiev of one scholar. It belongs rather to the article Mithraic Mysteries, which this question actually is handled. In this article, a much shorter mentioning of this hypothesis would be enough, but of course, there should be a link to the article Mithraic Mysteries. Indeed, that section could be replaced with a more general one, with headline "Astrological, mythological and religious interpretations", or "Effects on astrolgical beliefs and religions", or something like that. There namely are (or have been) quite a few religious beliefs which have at least sometimes been interpreted as inspired by the fact of precession; Mithraic mysteries are just one example among others. According to some scholars (as I have somewhere read, I do not remember where), even the fish ( Ikhthus) as an early Christian symbol, generally thought to be just an acronym, might have been inspired by the fact that what astrologers call " Age of Pisces" (Fishes) had begun just a little before the time of Jesus. - KLS ( talk) 11:23, 14 January 2016 (UTC)
IceDragon64 ( talk) 23:02, 15 July 2018 (UTC)
I would like to see some graphic which depicts the Earth's inclination in relation to the sun when Vega is the pole star in another 12,000 or so years. Vega will have scarcely changed its relation to our solar system in this time (in fact, it is reputed to be moving directly towards us, and we towards it). But Vega lies (now) at a current astronomical latitude of about 39°N., some 50+° away from Polaris. Given that the angle of obliquity, when doubled, equals this 50° more or less, and Vega is completely on the other side of the path through the heavens described by the polar axis, my comment could perhaps be labelled correctly as an inability to visualize what the future inclination of the planet will be. However, I can conceive that significant changes in which areas of the Earth would come directly under the sun, and also that the yearly periods of their being under the sun would change drastically. Would the angle of obliquity of the axis always remain between ~24° and ~21°? Obviously the apparent positions of the stars in the skies will change, as they have changed before, but I would like to read something from a knowledgable source about what this means in relation to apparent latitude of the sun as seen from different areas of Earth. A good graphic would help. Not meant to be a criticism of any one or any theory. — Preceding unsigned comment added by Daniel Sparkman ( talk • contribs) 09:58, 11 May 2016 (UTC)
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There are many statements in the article about the period of precession. The last section gives a general discussion of the fact that different models are designed to maximize accuracy over time periods chosen by the modelers, and those periods may be much less than one precession cycle. I would like to see various precession values made consistent throughout the article when they are valid for the same time span. I also think that the more general, introductory statements should use values that are valid for at least one full cycle, because that is how non-specialist readers will think of a precession cycle, not a small fraction of a cycle centered around AD 2000. Jc3s5h ( talk) 20:56, 18 May 2018 (UTC)
I think this paragraph is probably written by somebody who already fully understands the Indian references, but doesn't make much sense to me. I'm sorry I can't do it myself, but in order to gain much information from it, it needs to be fully translated into scientific English.
IceDragon64 ( talk) 22:50, 15 July 2018 (UTC)
The Standard Gravitational Parameter is usually given as µ (lower-case Greek mu) rather than Gm or GM.
I'm reluctant to make an arbitrary edit for fear of hurting readability/usability of the formulae.
My citation for making this statement is /info/en/?search=Standard_gravitational_parameter.
216.145.100.72 ( talk) 21:40, 1 September 2018 (UTC) -- Ian Moote
Article missing constellation list earth precision pass trougth:
Ursa Minor Draco Hercules Lyra Cygnus Cepheus
Axet ( talk) 09:39, 10 April 2019 (UTC)
The pole does not depict the closed circle. The inclination of the Earth's axis is changed [7]. Because the Earth’s orbit is also precessing [8] about 4 degrees [9]. Voproshatel ( talk) 05:51, 4 September 2019 (UTC)
More correct trajectory http://www.astrokot.kiev.ua/slovar/images/precessiya.gif or https://rutlib5.com/book/7353/p/i_007.jpg Voproshatel ( talk) 06:11, 9 November 2020 (UTC)
Yet more correct trajectory against the still sky of the epoch J2000.0 ru:Файл:Прецессия_северного_полюса_Земли.png Voproshatel ( talk) 18:09, 2 February 2021 (UTC)
The 3rd image on the page, provided by user Cmglee, appears to illustrate Apsidal Precession, the variation of Perihelion and Aphelion over an approximate 20,000 year cycle, rather than Axial Precession, which varies with an approximate 26,000 year cycle. -- George Fergus ( talk) 02:59, 22 December 2019 (UTC)
Has anyone a photo available to visualize the precession effect in an actual celestial observation everyone could see with their own eyes and a clock? What would be better to visualize: the change of the local solar time of the day of the midnight culmination of a star from year to year or the change in maximum elevation the midnight culmination of a specific star reaches? Stars near the celestial equator should show the largest effect and near the celestial pole the smallest in my understanding. My guess would be the time of the midnight calculation is easier to measure it should move by a maximum of 3.34s if I understand the discussion here correctly. All my consideration was of course with ignoring the individual proper motion of a star. Isenberg ( talk) 04:06, 3 November 2023 (UTC)
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The astronomical formulas I have seen appear to be based on working back from known observational data (e.g., the earth's precession around the Ecliptic Pole, the Anomalous Precession period, the Lunisolar Precession period, Apsidal (Perihelion) Precession and the "Mercury Question", etc.).
Is there an actual standard formula that exists to calculate precession? Specifically, one that allows the user to enter applicable values (mass of the bodies, distance, orbital period, rotation period, obliquity, etc.), and come up with the precession value? Such a formula should work with any given value (including values given for any hypotheical planetary system).
Unless such a formula exists in the scientific community, I tend to agree with those who hint that determining Precession remains an open-ended mystery (at least regarding both its cause and its affect outside calculations based on direct observation).
Granted, any standard formula would only be accurate to so-many decimal places (due to not being able to account for ALL the multitude of minor gravitational influences from lesser bodies throughout any given system and beyond). Nevertheless, if science has determined the true cause and affect of precession, then a standarized formula (with known-body input values)should exist. Otherwise, any questioning mind may be justified in questioning the existing theories.
The many with greater knowledge may know of such a formula. If so, may it be included on the Wiki page? Oh ... and it would be super if it was written in a manner that is can be interpreted by mathematically limited individuals (who, me?!). -- Tesseract501 06:10, 12 October 2008 (UTC)
Yes, there are many precession nutation models, the most comprehensive is the 2000A model with almost 1400 terms. The problem is the models are "not consistent with dynamical theory" according to the International Astronomical Union (IAU 2006 P03). Also, while the models find a value close to the observed rate they have been unable to predict "changes" in the precession rate (such as the constant increase in the rate over the last few hundred years). Consequently, the models are revised or modified every few years to better match precession observations. This has been going on since d'Alembert substantially modified Newton's formula which did not work. Of course the changes keep getting smaller but one has to wonder if many of the unknown dynamic assumptions (concerning the shape and viscosity of the earth's core, etc.) are included to make the model fit the observable. Interesting area of study. —Preceding unsigned comment added by 69.234.46.179 ( talk) 21:33, 16 November 2009 (UTC)
The section referring to precession of the equator should be deleted ASAp unless a reference supporting the assertion that `precession of the equinoxes' has been replaced by 'precession of the equator' Terry MacKinnell ( talk) 22:52, 27 February 2009 (UTC)
It's not very clear who these 'pre-modern' astronomers are supposed to have been, who called it the 'precession of the equinoxes'. Plenty of sources show that up to about the end of the sixteenth century AD, which is pre-modern if you like, it was often called 'the motion of the eighth sphere' (e.g. 'De motu octavae sphaerae', I.Werner, Nuremberg, 1522). 'Precession of the equinoxes' is a _relatively_ modern term.
It's also not very clear that the term 'precession of the equinoxes is out of date, either. It's not equal to either the 'precession of the equator' or the 'precession of the ecliptic' -- it's the combined effect of the two of them together. Is there a replacement terminology for that? —Preceding unsigned comment added by 86.14.225.140 ( talk) 18:15, 1 March 2009 (UTC)
Isn't the direction of the precession wrong in the picture? The angular momenta is supposed to be conserved and thus the precession must be in the same direction as the body is spining. Besides I actually found another copy of the same image on the internet with the correct direction of the precession.
Samuel —Preceding unsigned comment added by 83.250.175.92 ( talk) 22:23, 5 March 2009 (UTC)
No! Precession is in the opposite direction to the spin - otherwise it would be called PROcession of the equinoxes! TomNicholson ( talk) 15:33, 18 November 2009 (UTC)
If the Earth's axis of rotation is orthogonally projected to the plane of the solar system, is the projected direction parallel to the major axis of the orbit? If so, is there an explanation of such a phenomenon in gravitational terms? 132.70.50.117 ( talk) 10:23, 5 May 2009 (UTC)
When does the current precession cycle finishes? Echofloripa ( talk) 23:14, 16 July 2009 (UTC)
Zbayz changed the name of this article from "Precession (astronomy)" to "Axial precession (astronomy)" without any discussion whatsoever. His stated reason was "This article only discusses precession of the rotational axis. It says nothing about perhelion precession." both of which are wrong. Although the dominant focus of the article is 'axial precession' it does mention "planetary precession" now renamed "precession of the ecliptic" and "anomalistic precession". The proper name for 'axial precession' is either the old name "lunisolar precession" which was used for at least two centuries or its new name, since 2006, "precession of the equator". Furthermore, this article mentions "planetary precession" now renamed "precession of the ecliptic" which is the gradual change in the inclination of Earth's orbit relative to the invariable plane of the solar system and the combination of "precession of the equator" and "precession of the ecliptic" which is called "general precession" and has been so named for at least one and a half centuries. This article also has a section on "anomalistic precession" at the end of the article, which Zbayz calls "perihelion precession", but refers to an article named apsidal precession.
Zbayz also did not follow Wikipedia naming conventions for disambiguating articles. Do not use a parenthetical qualifier unless two or more articles have the same name. — Joe Kress ( talk) 22:42, 25 August 2009 (UTC)
I suggest to split out astronomic scientific material of this article and through out pseudoscience astrological data. There is no reasons to cover both this topics in the article. Astrology - is a cultural phenomenon, not the science. Thank you. —Preceding unsigned comment added by 95.133.136.138 ( talk) 14:14, 7 September 2009 (UTC)
Are you suggesting that science is not a cultural phenomenon? TomNicholson ( talk) 15:36, 18 November 2009 (UTC)
Astrology was (and for a long time) the reason for astronomy. I notice it has lost cultural colective favour (except in Biblical instances such as the star of Bethlehem, kings choosing when to procreate etc - where it is regarded as a part of gods plan) When you say ' through out' pseudoscience astrological data. I presume you mean - 'throw out'. This vandalism you blithely propose is just that. 188.220.186.57 ( talk) 15:29, 30 August 2011 (UTC)
From the Effects Para:
Thus, the tropical year, measuring the cycle of seasons (for example, the time from solstice to solstice, or equinox to equinox), is about 20 minutes shorter than the sidereal year, which is measured by the Sun's apparent position relative to the stars. Note that 20 minutes per year is approximately equivalent to one year per 25,771.5 years, so after one full cycle of 25,771.5 years the positions of the seasons relative to the orbit are "back where they started".
I calculate that 20 minutes per year gets 360 degrees of precession in 72 years not in 25,771.5 years. What's going on here? Who did this math? Lkoler ( talk) 04:53, 16 October 2009 (UTC)
I agree with Lkoler. Common sense indicates otherwise. 20 extra minutes per year? There are 24 hours in a day. 20 minutes is 1/72 of 24 hours. Certainly, the stars(celestial sphere) are not adjusting 1/72 every year. That would put precession at super speed and we would be cycling through the constellations every 72 years. Something is wrong in the math. Common sense just doesn't support it.
If time passes by, then the celestial sphere moves. Actually, the celestial sphere moving is the cause of the time measurement, not the other way around. So, if the celestial sphere moves 20 extra minutes from what it was the year before, it must move 1/72 of the angle of the sky. 360 degrees multiplied by 1/72 is 5 degrees of the sky every year. And (divide 5(18,000 arcseconds) degrees by 365 days)would have to move about 50 arcseconds every day. This does not happen.
Remember, an extra 20 minutes per year would mean the celestial sphere shifts 5 degrees every year, and 50 arc seconds per day. It's not 50 arc seconds per day, it's 50 arc seconds per year. Hipparchus could tell you that. It's obvious, but a lot of people are getting it wrong for some reason.-- Markblohm ( talk) 18:10, 8 December 2009 (UTC)
An extra 20 minutes causes the earth to point 5 full degrees different in relation to the stars. Just like an extra 12 hours would cause a 180 degree change. Think about it. 1 tropical year is when the sun is back to the same position in relation to the earth. A tropical year plus 12 more hours would have us facing the opposite way. Likewise, 20 extra minutes would have us facing 5 full degrees off from the previous. Say at time zero you are facing 0 degrees angle. 1 day later you are also facing 0 degrees angle. 100 days later, still 0 degrees angle. 1 tropical year later exactly, and you are facing 0 degrees angle. But what is being said is that 20 more minutes is being added to the tropical year. That is 5 full degrees extra of the celestial sphere(because we have a 24 hour day). 1 tropical year later, the sun is in the same position. The shift is 50 arcseconds of the celestial sphere/year(this shift of 50 arcseconds has been observed for a long time, and is much less than 20 minutes.-- Markblohm ( talk) 21:06, 8 December 2009 (UTC)
I now understand why the time of around 20 minutes is being found. The math is not wrong. The equation is wrong. Precession is independent of the spin of the earth, so to account for the total seconds of the spin of the earth in a year when finding the real time change of precession is incorrect. Even if we say that it is wobbling, the wobbling is occurring independent of the spin. The "wobble" is only about 50 arcseconds, and is independent of the spin of the earth. We add the extra wobble time onto the total spin at the end of the year. After all, 50 arcseconds of angle(or 3.3 seconds of real time) is the change each year, which is clear to observing astronomers in the past and present.-- Markblohm ( talk) 01:47, 9 December 2009 (UTC)
No matter what equations you throw up, 50 arcseconds can never be anything other than 3.3 seconds of real time, just as 180 degrees can never be anything but 12 hours of real time. The spinning earth arcseconds do not get factored into the precession equation. You have made the very common error.-- Markblohm ( talk) 01:58, 10 December 2009 (UTC)
It appears to me that Lkoler and Markblohm are consistently confusing two kinds of circular motion. 50 arcsec of daily rotation takes 3.3 sec "of real time", but 50 arcsec of annual revolution takes 365 times as long. But that's so obvious that someone ought to have pointed it out by now, so have I missed something? — Tamfang ( talk) 06:04, 10 December 2009 (UTC)
Ah, but we're not measuring 50 arcseconds of annual revolution. If we measure 50 arcseconds of annual revolution(earth's orbital circumference) then we do get 20 minutes. It indeed takes 20 minutes for the earth to travel 50 arcseconds of the orbital circumference. But the observed 50 arcseconds of celestial sky movement is 1/365 of that. Because the earth spins 365 times in its orbital revolution. That is what the famous 50 arcesonds is, 50 arcseconds of celestial sky displacement viewed from the earth every year, cumulative for the whole year. An ancient astronomer like Hipparchus only observed 50 arcseconds of celestial sky displacement per year. He could not have observed 50 arcseconds of the orbital circumference.-- Markblohm ( talk) 15:26, 10 December 2009 (UTC)
Hi Joe(Kress.) May I ask, why are you multiplying 50" by 365?-- Markblohm ( talk) 16:07, 10 December 2009 (UTC)
Dear Tamfang, You have highlighted the problem exactly. I assume by double rotation period you mean two times faster. But even if you mean two times slower it doesn't matter. If the earth were spinning(rotating) at double it's current speed(and precession rate remained the same), the precession rate would be exactly 3.3 seconds. The seasonal year would still be the tropical year length PLUS the 3.3 seconds. The spinning earth doesn't multiply the precession, which is what is being said in these equations above. You are multiplying the precession time by the amount of days. That is incorrect. The precession movement is independent of the spinning, so you must ADD the extra precession time onto the length of the tropical year.
The sun "travels" in the sky 473040000arcseconds(365(roughly) x 360 degrees) in one year. The celestial sky travels 473040000arcseconds PLUS 50 arcseconds. In other words, the sun travels 31536000 time seconds(525600 minutes) in one year. It then takes 3.3 seconds(50 arcseconds) to catch up on the vernal equinox. These arcseconds/time seconds have been accumulating all year. On the half year the sun would take only 3.3/2 seconds(25 arcseconds to catch up). The sun travels through the sky roughly 473040000arcseconds in one year, the celestial background is travelling 473040050arcseconds.-- Markblohm ( talk) 20:23, 10 December 2009 (UTC)
Markblohm: My equation for the annual precession time is independent of Earth's rate of rotation. If Earth rotated twice as fast, its day would be half as long, 43,200 seconds, but the number of those shorter days in a year would be twice as many, 730.5 days, so there would be no change in the precession time in a Julian year, 20.42 minutes. The angular speed of the Sun in its apparent orbit around the Earth can also be used to determine the time it takes an equinox to precess along the ecliptic in one year. The Sun moves at an average speed of (1,296,000"/yr)/(365.25 days/yr) = 3548"/day. Hence the annual precession time is (50.29"/yr)/(3548"/day) = 0.014174 day/yr = 20.4 minutes/yr. You agree that this is correct via your statement "It indeed takes 20 minutes for the earth to travel 50 arcseconds of the orbital circumference." But you then state "An ancient astronomer like Hipparchus only observed 50 arcseconds of celestial sky displacement per year. He could not have observed 50 arcseconds of the orbital circumference." To Hipparchus these were a single concept. A little history is warranted:
Hipparchus and Ptolemy regarded the Universe as the stars, five planets and the Sun and Moon all revolving around a motionless Earth at their center. The orbit of the Sun around Earth (the mirror image of Earth's orbit around the Sun) marked the ecliptic, which was also the center of the zodiac, a band which contained the orbits of the Moon and the five planets. But the dominant motion (now known to be due to Earth's own rotation) was parallel to the celestial equator, which was inclined to the ecliptic by 23.5°. Hipparchus discovered that the stars had an additional motion parallel to the ecliptic called precession. A ring mounted in the plane of the equator was used to determine the date/time of the equinoxes, which occurred when the shadow of the Sun cast by the upper part of the ring fell on its lower part, meaning that the Sun was crossing the equator from south to north or vice versa. The location of the equinoxes and solstices among the stars was determined using the Moon as an intermediary because it was visible both during the day and night.
Hipparchus determined that the ecliptic longitude of Regulus, a star within 0.4° of the ecliptic, was 295⁄6° east of the summer solstice (119.8° east of the vernal equinox) in 129 BC. Ptolemy determined that the longitude of this same star was 321⁄2° east of the summer solstice (122.5°) in AD 139, so Ptolemy noted that the star had moved 22⁄3° in 265 years (we now say the summer solstice moved, not the star). From this he concluded that precession was 1° in 100 years or 36"/yr, the same precession that Hipparchus had deduced (precession is now known to be 1° in 72 years or 50"/yr). Today (J2000), Regulus has a longitude of 150.2°, so the solstices and equinoxes have precessed 30.4°, about one zodiacal sign, in 2,129 years, a precession of 51.4"/yr (using Hipparchus' imprecise position), about the same as the modern value. Hipparchus and Ptolemy used twelve zodiacal signs of 30° each to measure longitude. Precession measurements never used or depended upon either the solar day or the sidereal day. They also determined the angular distances (called declinations) of those stars north or south of the equator. They noted that stars near the autumnal equinox which were north of the equator later moved south of the equator (south to north near vernal equinox). Both methods resulted in the same precession. This "celestial sky displacement" was along the ecliptic, which was the "orbital circumference" of the Sun's orbit.
By the 18th century, astronomers no longer needed to use ancient observations, but were able to determine precession by comparing the positions of stars determined at times less than a century apart. These modern astronomers also discovered that some stars had large proper motions ( Sirius moves about 1.3" every year), which had to be excluded from those stars used to measure precession. The pointing accuracy of the largest telescopes is now about 5", so precession is observeable within one year and must be considered to even locate stars at high magnifications if a star catalogue several years old is used.
Although you state that the spinning Earth does not multiply the precession, that is exactly what you do via "(365(roughly) x 360 degrees)". — Joe Kress ( talk) 22:35, 15 December 2009 (UTC)
This image, currently shown at the top of the page, is confusing in that the rotation of the axis is shown to be in the same direction as the spin of the planet. A reading of the description (click on the image to go to the image page and see the summary below) reveals that the axial rotation shown in this image is "relative to the direction to the Sun at perihelion and aphelion", (ie. it relates to orbital precession - even though the orbit is not shown), rather than axial precession, the title of this page. The commonly understood meaning of the unqualified term "precession" is axial precession relative to the fixed stars, where it moves counter to the spin (hence the term PREcession, rather than PROcession).
This image appears here: http://earthobservatory.nasa.gov/IOTD/view.php?id=541 with the words "orbital precession" at the top. Why have these words been removed? Is someone purposefully trying to confuse here? TomNicholson ( talk) 16:57, 18 November 2009 (UTC)
I would edit this section directly if it were not for the fact that the image has errors, and I don't have a replacement.
The vertical cyan (pale blue) arrows and the yellow arrows (shown at the equator) indicating the torque should not be present at the equinoxes - the symmetry of the earth-sun relationship at the equinoxes (and hence the lack of torque) is more clearly seen if the orbital motion (which is irrelevant) is ignored, or with reference to the first equation in the following section where it is seen that the torque vanishes at the equinoxes when delta (and sine delta) become zero. This is mentioned in the text: "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, at the equinoxes.
Is anyone else bothered by the statement, "This average torque is perpendicular to the direction in which the rotation axis is tilted away from the ecliptic pole, so that it does not change the axial tilt itself"? It is the axis of the average torque which is perpendicular to the direction in which the rotation axis is tilted away from the ecliptic pole, and I don't believe it is obvious why this does not change the axial tilt itself. Actually, the "force" of the torque tends to "want" to lessen the axial tilt - a tendency which is thwarted due to the (counter-intuitive) properties of spinning objects. If at this point you think I'm completely crazy :) then try the following ...
Take a bicycle wheel (minus the bike) and hold the spindle in your hands so that your arms are like the front forks of the bike. Spin the wheel. Now (carefully!) try and change the axis of rotation. Weird, isn't it?!
TomNicholson ( talk) 18:07, 18 November 2009 (UTC)
The Introduction mentions a period of 26,000 years and a cone of unspecified size and direction.
A cone is not necessarily circular.
I think that it would be well to indicate, in the introduction (but not necessarily in these terms), that the direction of the Earth's axis of rotation moves in a circle of radius 23.5° about the Earth's orbital axis ; and that the current direction of motion is approximately along a line from Polaris towards some other well-known star. The one which it will be near in AD 4000 might suit ; perhaps in Cepheus, probably Gamma, I think - or maybe use the Great Square.
The circularity and size are present, buried lower down.
82.163.24.100 ( talk) 14:33, 24 November 2009 (UTC)
Could someone perhaps take a look at the related Great Year article? A number of questionable edits have been made recently. The new "Confusion of the Platonic Year with Precession" section may be of particular concern. Pollinosisss ( talk) 07:20, 14 December 2009 (UTC)
In 12,850 years, will the date of the vernal equinox in the Northern Hemisphere still be March 20th or will it be October 20th? Why has the date decreased from March 22nd a century ago to March 20th now? Keraunos ( talk) 16:14, 1 January 2010 (UTC)
Thank you so much for the clarification. I had always wondered about that problem. Happy New Year 2010! Keraunos ( talk) 11:06, 2 January 2010 (UTC)
If the article is going to discuss Mithraism in detail, it might as well give a nod to "tropical astrology" vs. " sidereal astrology" and the so-called " Age of Aquarius"... AnonMoos ( talk) 13:03, 15 January 2010 (UTC)
The Articles INTRODUCTION is overly complex and therefore poorly explained .The diagrams a bewildering to none-astronomers.Is this the object of wikipedia? A celestial sphere, the sun at the centre with a zodiac ring drawn as a band on the sphere, would be a better introduction.This would: (a) Root the observations to a fairly universally known (and therefore familiar) set of coordinates. (b) Remove the visual confusion (c) Allow for a clear intersection planes to be inscribed on the sphere. I would butte in a fix it myself but its really up to those most impassioned in this debate.Anyway were does a layman get the computer program to generate the diagrams?Ha! —Preceding unsigned comment added by Chasludo ( talk • contribs) 23:55, 16 January 2010 (UTC)
I moved Cuvier's 1825 estimate (recently added by Hmschallenger) to the Middle Ages onwards section, at least temporarily. It certainly does not belong in the Hipparchus section just because it uses observations by Hipparchus. It should be in a "modern estimates" section which currently does not exist. A good start would be Evolution of adopted values for precession by Jay H. Lieske. — Joe Kress ( talk) 23:54, 24 January 2010 (UTC)
I cannot see a credit at
http://www.crystalinks.com/precession.html
to this article.
There is a simple one link on a line by itself that is labeled "wikipedia" but no indication that the article is copied. The link is not labeled "orginal wikipedia article" or the like. I cannot see that the mere label "wikipedia" constitutes either a reference or credit and the owner appears to have a commercial site (psychic this or astrological that)
In the case of
http://encycl.opentopia.com/term/Precession_of_the_equinoxes
there is a fine print credit to wikipedia without actually naming this article. —Preceding unsigned comment added by Grshiplett ( talk • contribs) 00:52, 4 March 2010 (UTC)
In the section about Mayans it states that professional scholars do not hold the opinion that the Mayans where aware of precession. The reference is written by a Mayan scholar who does hold that opinion and states her opinion uncategorically in the article by saying... "The end of the baktun on the winter solstice is not a coincidence, and this mathematical feat is certainly a sign of a sophisticated link between Maya astronomy and mathematics." Yourliver ( talk) 14:46, 11 May 2010 (UTC)
There's some dispute here about what causes precession of the equinoxes. I got rid of the picture, which I think is misleading. My edits have been largely reverted here: [3]. There is more discussion here: [4] if anyone is interested. ErikHaugen ( talk) 23:03, 14 June 2010 (UTC)
Here is the summary, as I see it: There are two competing explanations for precession of the equinoxes. At least one is totally bogus. The first considers the "vertical"(north/south) and "horizontal"(sunward) components of the forces on the halves of the bulge by the sun - the vertical components point in opposite directions and cause a torque. The second, (which I assert is right), is that the difference in magnitude, due to the difference in distance to the sun, causes a torque, since the sun pulling on the closer half of the bulge causes a torque in one direction, and the sun pulling on the far half of the bulge causes a torque in the other direction - the close half wins since the distance to the sun is closer. Note that the two explanations disagree on basic things like "At the solstice, in what direction is the torque caused by the sun pulling just on the far half of the bulge?" And also note that the first explanation does not have anything to do with the inverse square law and gravity getting weaker with the difference in distance. Please say if you do not agree with this assessment. To resolve, can we cite sources? ie, can someone suggest a particular page of a particular astronomy book? (I'd sure appreciate one that freely available online.) I'll offer:
I still think you are mistaken, and so are many others, and in fact it is very difficult to find any literature about precession which try to explain the cause. Most quickly pass this part and then directly jump to the results. There are some however:
Looking at this picture we see the vectors of the differential gravitation for different angular distances from the disturbing body. It is true that there is no tangential component whatsoever if the sun/moon are on the equator, so no precession takes place. But that does not mean that there is none at the equinoxes. Because the equatorial bulge is not a single point, it is still a whole ring. That is the crucial issue. Even if during the equinoxes the point of the bulge 'under' the sun is on the equator and not doing anything, the extreme (solstice) points are then on the terminator, and they still are subject the tidal force towards the equator. In fact it does not matter where the sun is somewhere, equinox, solstice or somewhere in between, that part of the bulge north of the equator experiences a force to the south (strongest at the northernmost part, going down to zero to the equator) and vice versa for the southern half. The two forces of course are part of a torque, and there the precession begins. It also means that the precession force is always the same, the whole year around (or the whole month around if you talk about the moon). How otherwise could the precession speed of 50" per year be a constant (ignoring secular changes and the several magnitudes smaller irregularities of the nutation) as everybody agrees ? No astronomer has ever observed that precession would come to a standstill at the equinox and reach full speed at the solstice; it just progresses at a constant rate during the year (and the month).
So the torque does not change over time. What does change on the bulge when the sun (or moon) appears to go round the ecliptic plane is the strength of the radial component, the difference being largest at the equinoxes. But a radial component does not contribute to a torque. If there is anything 'bogus' there is that.
Please restore the picture. It is still correct.
What about the quote of Kaler and others above? I am sorry, no doubt dr Kaler is an excellent astronomer, but he is specialised on stars and nebuale, and therefore less at home in celestial mechanics. His statement on variable precession is utterly wrong. -- Tauʻolunga ( talk) 08:51, 15 June 2010 (UTC)
Right now, this page redirects from Axial precession. But since there is no other type of axial precession, there doesn't appear to be a need for a qualifier at the end. Serendi pod ous 18:07, 10 April 2011 (UTC)
By consequence, the constellation is no longer visible from subtropical northern latitudes, as it was in the time of the ancient Greeks.
How are we defining 'subtropical northern latitudes' here? Because I'm at about 25N, and I can see the top half of the Southern Cross from my driveway, 'in the city', when it's a sufficiently clear night. Around March, to be specific. I imagine it's a much better view in the Keys, with the clearer horizons.
I am hesitant to revise that line without either the original justification for it referenced, or what documentation on my part would be appropriate.
Corgi ( talk) 14:28, 15 July 2011 (UTC)
What is the tilt of the precession central axis with reference to the ecliptic of the sun, seeing that tidal torque forces from the moon are stronger than the sun's tidal forces, and the moon's orbit is not aligned with the solar ecliptic, defined by earth's orbit about the sun? The precessional central axis should be on a tidal torque coordinate that is a mathematical mix between the stronger lunar orbit tidal torque, and the weaker solar ecliptic tidal torque, and as such would also shift solar and lunar positions on horizon reference points, with the precession period over the approximately 30,000 year period. With an ecliptic-reference tilted central precession axis, these precession effects would misalign the claimed thousands of year old monuments based on the precision of solar and lunar horizon reference points on claimed ancient precise stone monuments like Stonehenge, and other ancient horizon reference stone marker systems. At least hyperbole, in media claiming such monuments still have "exact" alignments, whatever the word "exact" means in media. Only monuments aligned to the earth's own axis, like The Giza Pyramids, would remain constant, of course pointing to a moving pole, as the star charts show with Polaris today, or Thuban, or Vega, at other points on the precession path. Not to mention systems of stellar alignment, like claimed Nazca Lines, pointing to Sirius and Orion, seem to be media hype, having nothing to do with the Ecliptic, and claims of ancient formation toward these alignments, which will definitely not hold over thousands of years. LoneRubberDragon 76.166.233.62 ( talk) 06:54, 5 August 2011 (UTC)
User:TomNicholson would have us believe that precession and procession are opposites, which is news to me. The two words come respectively from (the Latin ancestors of) precede, 'go before (something else)', and proceed, 'go forward'. Let's either have some support for the claim or delete the new section asserting it. — Tamfang ( talk) 21:13, 24 December 2011 (UTC)
I'm replacing a couple of the graphics with some animations - in particular, the two depicting "inside the celestial sphere" and "outside the celestial sphere". We will need to update the text immediately under them to reflect the new graphics. Tfr000 ( talk) 18:34, 9 May 2012 (UTC)
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What angle is the cone made by Earth's rotational axis in the first illustration? The article begs the question. Maybe add it to that first illustration. I'm still not sure, my best guess is 23DEG based on the article.
Pb8bije6a7b6a3w ( talk) 23:23, 27 February 2013 (UTC)
The rotation axis of the Earth describes, over a period of 25,700 years, a small circle (blue) among the stars, centered on the ecliptic north pole (the blue E) and with an angular radius of about 23.4°. Please feel free to edit the article to make this more clear, if that is what you meant. ErikHaugen ( talk | contribs) 17:42, 28 February 2013 (UTC)
I think the section called Equations is unclear. You see equations but it is not at all clear how they were derived. The reason for choosing an ecliptic plane coordinate system is unclear, An earth center fixed, non-rotating coordiante system with x and y in the equatorial plane, z along the earth polar axis positive north and with x pointing in the vernal equinox direction positive seems to be much better. The derivation in Meirovitch's "Methods of Analytic Dynamics" is much clearer in my opinion.
From the introduction: "...although evidence from cuneiform tablets suggest that his [Hipparchus'] statements and mathematics relied heavily on Babylonian astronomical materials that had existed for many centuries prior..." It'd be great to have a source for this to reference. The History material later in the article doesn't provide a source for this either. Any ideas anyone? Bob Enyart, Denver radio host at KGOV ( talk) 17:18, 29 June 2013 (UTC)
Please split topic.
This section is about precession whatis and maybe short cause with lead to other topic: the usual.
It's not a topic to cut and paste earth moon / earth body formulas (and words) from likely copyrighted books ! that MIGHT contribute to precession. MIGHT.
Please create a new topic for that. I vote: split
BTW. current theory is moon hit earth which would give it INITIAL precession. the equations are paste they assume no initial precession and do not imply whether or how precession would continue or balance if the newtonians frame forces were removed.
another concern the equations mention forces two non-parallel as contributing (didn't cancel.) HOWEVER. it said nothing about, say, 250000 (or any) yrs later when THE OPPOSITE SIDE would get the same treatment thus almost wholey cancel the unbalanced forces mentioned
the formula is there (needs many conversions to use: T). and the precession itself is bound to be constant rate and rate (like a top) and is tabled in article.
but for an easier to use formula for effect on season length, see tropic year in wikipedia it has a good equation and tables
The illustration shows the axial precession of the Earth. Looking at it it would appear to me that half way through, the Earth is tilted the opposite way from the beginning of the circle and in that case summer would be reversed (if at the beginning of a cycle, summer is June 21 - Sep 21 or so in the northern hemisphere, then half way through the cycle June 21 - Spe 21 would be winter in the northern hemisphere). I suppose that is not true but that is how it looks doesn't it?
== tc
OK. But it is true then, right, that the perihelion (now in winter) and the aphelion (now in summer) will at times be switched (perihelion in summer and aphelion in winter)? I think I got those terms right. There is also apogee. — Preceding
unsigned comment added by
63.84.231.3 (
talk)
13:08, 2 July 2014 (UTC)
The blending of art and science greatly hinders each and every scientific discipline that is contaminated. I wish there was a more gentle word, other than "contaminate," because imagination and creativity are crucial traits for a species to have, however, when the line that separates what we know from what we think, gets blurred, we eventually get flat out false assumptions accepted by the masses as truth. The precession of Astronomers and Astrophysicists from sort of right to completely wrong and then back to almost accurate observations is the only thing that occurs. And if Astronomers and Astrophysicists could be honest enough to just admit the things that we don't know with scientific certainty, so that it doesn't get confused with things we know with certainty, We wouldn't be so lost and argumentative with Our knowledge of how things work. Scientists do not debate like this, peer review does not mean hold a debate to discern the Truth. And this subject is a perfect example of the nonsense that gets accepted as fact. These subjects are why the world still, to this day, believes the Moon causes the tides of Our Oceans, or that Our Solar System is hurdling outward in a straight line which fools somehow think proves the expansion of space. The ego of men and the feeble minds which encourages arguing for one exaggerated false claim over another, and Our allowing foolish men and their false theories to be accepted as facts, has severely hindered humane beings' ability to understand this world. And that is sad. - Dirtclustit ( talk) 13:14, 21 August 2014 (UTC)
@Dirtclustit: Nice. Far too much certainty given to hypotheses in most sciences.
In the section 'equations' there is:
T = 3GM/r^3 ...
I don't see any support for that not other result, and none of references to this solution also. What this is a pseudoscience or religion? — Preceding unsigned comment added by 217.99.107.103 ( talk) 00:06, 12 December 2014 (UTC)
17:38, 28 December 2014 (UTC)17:38, 28 December 2014 (UTC) 83.26.156.68 ( talk) 17:38, 28 December 2014 (UTC)
http://adsabs.harvard.edu/abs/1994AJ....108..711W
I don't see there any derivation, just this same formulas - the final. BTW. The suppositin the potential of an oblate spheroid is responsible for a precession of the same spheroid is wrong, because the momentum can be conserved in other way, for example the orbital momentum can change accirdingly.
The method of solution and these formulas are adequate for a satelite's orbital precession of the Earth, but not for the Earth itself.
The suppositin the potential of an oblate spheroid is responsible for a precession of the same spheroid is wrong, because the momentum can be conserved in other way— Can you rephrase this? I'm not sure what you're saying. In particular, are you suggesting a change to the article? Can you be more specific about the change you'd like to see? ErikHaugen ( talk | contribs) 19:16, 30 December 2014 (UTC)
00:50, 7 January 2015 (UTC) 217.99.238.57 ( talk)
"The term (C−A)/C is Earth's dynamical ellipticity or flattening, which is adjusted to the observed precession because Earth's internal structure is not known with sufficient detail."
So, it's rather evident it's just a manipulation of numbers, not any real solution.
What is a precession speed of a massive ring or disk inclined at angle i, and spinning with speed w?
No valid observation has been made across 26,000 years yet. It is unproven, so the title of the article must be presented as an experiment in vitro. All information should be re-evaluated in this regard. The article must be changed to "Axial Precession Theory", as written in heading of this new section. — Preceding unsigned comment added by 72.94.152.209 ( talk) 12:18, 26 February 2015 (UTC)
It seems to me very questionable if the section "Mithraic question" belongs here at the present length, or at all. At least most of it is wholly outside the topic. It is not even known whether Mithraic Mysteries had anything to do with the precession at all; it is just the wiev of one scholar. It belongs rather to the article Mithraic Mysteries, which this question actually is handled. In this article, a much shorter mentioning of this hypothesis would be enough, but of course, there should be a link to the article Mithraic Mysteries. Indeed, that section could be replaced with a more general one, with headline "Astrological, mythological and religious interpretations", or "Effects on astrolgical beliefs and religions", or something like that. There namely are (or have been) quite a few religious beliefs which have at least sometimes been interpreted as inspired by the fact of precession; Mithraic mysteries are just one example among others. According to some scholars (as I have somewhere read, I do not remember where), even the fish ( Ikhthus) as an early Christian symbol, generally thought to be just an acronym, might have been inspired by the fact that what astrologers call " Age of Pisces" (Fishes) had begun just a little before the time of Jesus. - KLS ( talk) 11:23, 14 January 2016 (UTC)
IceDragon64 ( talk) 23:02, 15 July 2018 (UTC)
I would like to see some graphic which depicts the Earth's inclination in relation to the sun when Vega is the pole star in another 12,000 or so years. Vega will have scarcely changed its relation to our solar system in this time (in fact, it is reputed to be moving directly towards us, and we towards it). But Vega lies (now) at a current astronomical latitude of about 39°N., some 50+° away from Polaris. Given that the angle of obliquity, when doubled, equals this 50° more or less, and Vega is completely on the other side of the path through the heavens described by the polar axis, my comment could perhaps be labelled correctly as an inability to visualize what the future inclination of the planet will be. However, I can conceive that significant changes in which areas of the Earth would come directly under the sun, and also that the yearly periods of their being under the sun would change drastically. Would the angle of obliquity of the axis always remain between ~24° and ~21°? Obviously the apparent positions of the stars in the skies will change, as they have changed before, but I would like to read something from a knowledgable source about what this means in relation to apparent latitude of the sun as seen from different areas of Earth. A good graphic would help. Not meant to be a criticism of any one or any theory. — Preceding unsigned comment added by Daniel Sparkman ( talk • contribs) 09:58, 11 May 2016 (UTC)
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There are many statements in the article about the period of precession. The last section gives a general discussion of the fact that different models are designed to maximize accuracy over time periods chosen by the modelers, and those periods may be much less than one precession cycle. I would like to see various precession values made consistent throughout the article when they are valid for the same time span. I also think that the more general, introductory statements should use values that are valid for at least one full cycle, because that is how non-specialist readers will think of a precession cycle, not a small fraction of a cycle centered around AD 2000. Jc3s5h ( talk) 20:56, 18 May 2018 (UTC)
I think this paragraph is probably written by somebody who already fully understands the Indian references, but doesn't make much sense to me. I'm sorry I can't do it myself, but in order to gain much information from it, it needs to be fully translated into scientific English.
IceDragon64 ( talk) 22:50, 15 July 2018 (UTC)
The Standard Gravitational Parameter is usually given as µ (lower-case Greek mu) rather than Gm or GM.
I'm reluctant to make an arbitrary edit for fear of hurting readability/usability of the formulae.
My citation for making this statement is /info/en/?search=Standard_gravitational_parameter.
216.145.100.72 ( talk) 21:40, 1 September 2018 (UTC) -- Ian Moote
Article missing constellation list earth precision pass trougth:
Ursa Minor Draco Hercules Lyra Cygnus Cepheus
Axet ( talk) 09:39, 10 April 2019 (UTC)
The pole does not depict the closed circle. The inclination of the Earth's axis is changed [7]. Because the Earth’s orbit is also precessing [8] about 4 degrees [9]. Voproshatel ( talk) 05:51, 4 September 2019 (UTC)
More correct trajectory http://www.astrokot.kiev.ua/slovar/images/precessiya.gif or https://rutlib5.com/book/7353/p/i_007.jpg Voproshatel ( talk) 06:11, 9 November 2020 (UTC)
Yet more correct trajectory against the still sky of the epoch J2000.0 ru:Файл:Прецессия_северного_полюса_Земли.png Voproshatel ( talk) 18:09, 2 February 2021 (UTC)
The 3rd image on the page, provided by user Cmglee, appears to illustrate Apsidal Precession, the variation of Perihelion and Aphelion over an approximate 20,000 year cycle, rather than Axial Precession, which varies with an approximate 26,000 year cycle. -- George Fergus ( talk) 02:59, 22 December 2019 (UTC)
Has anyone a photo available to visualize the precession effect in an actual celestial observation everyone could see with their own eyes and a clock? What would be better to visualize: the change of the local solar time of the day of the midnight culmination of a star from year to year or the change in maximum elevation the midnight culmination of a specific star reaches? Stars near the celestial equator should show the largest effect and near the celestial pole the smallest in my understanding. My guess would be the time of the midnight calculation is easier to measure it should move by a maximum of 3.34s if I understand the discussion here correctly. All my consideration was of course with ignoring the individual proper motion of a star. Isenberg ( talk) 04:06, 3 November 2023 (UTC)