# Talk:Earth's rotation

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## German Wikipedia

This article needs more information. Maybe someone is able to translate something from the German Wikipedia. I do not have the time at the moment. Weird Bird 17:23, 27 August 2006 (UTC)

## Why does Earth rotate

It is not mentioned in this article why does the Earth rotate ? 202.68.145.230 14:18, 3 June 2007 (UTC) Amit Rana

Maybe the mentioned site http://curious.astro.cornell.edu/question.php?number=416 tells a good reason for Earth's rotation. 202.68.145.230 14:20, 3 June 2007 (UTC)Amit Rana

There is a section "origin of rotation" right now, which has good information, but for me it was not yet really clear why the earth was actually rotating. After consulting the above website, and another, im going to add it to the "origin of rotation" section. MrZap (talk) 14:02, 29 January 2008 (UTC)
Earth's present rotation period is the result of tidal friction slowing Earth's rotation from an initial value of about 6 hours 4.5 billion years ago to its present value of 24 hours. Any initial rotation acquired from the collapse of the primordial solar nebula was overwhelmed by the rotation imparted to the Earth by the tangential impact of the Mars-sized Theia/Orpheus. — Joe Kress (talk) 05:13, 30 January 2008 (UTC)
I added this, seems very plausible. Could not verify the extend to which factor would be the largest. MrZap (talk) 20:17, 20 March 2008 (UTC)

Related question: Is there any non-random natural explanation that might explain why the earth rotates one way instead of the other? Thanks. K61824 (talk) 19:31, 24 June 2009 (UTC)

Yes, the 18th century solar nebular hypothesis already mentioned causes all planets to rotate in the same direction as their orbital revolution. But we now know that two planets (excluding Pluto) do not obey this hypothesis, Venus and Uranus. These exceptions, plus Earth's rapid rotation (and its moon) prove that the solar nebular hypothesis is incomplete. The Late Heavy Bombardment period may explain these exceptions. — Joe Kress (talk) 00:36, 25 June 2009 (UTC)

But what about rotation of those planet not having any type of fluid Durgesh0 (talk) 05:54, 4 May 2016 (UTC)

## Introduction

Removed confusing remarks about magnetic compass from second sentence.CharlesHBennett (talk) 12:25, 2 November 2008 (UTC)

## Manifestations and evidence of rotation, Foucault Pendulum

Added section on Coriolis effect and early demonstrations of earth rotation based on the Coriolis effect in falling bodies, described in German Wikipedia. Condensed Foucault pendulum section. CharlesHBennett (talk) 09:19, 2 November 2008 (UTC)CharlesHBennett (talk) 12:25, 2 November 2008 (UTC)

## Earth's rotation speed

Can we remove all the high school physics? The earth is not 6,378,137 meters in circumference, that's about 3,963 miles. Russia is probably bigger than 4,000 miles. Let's just list the speed at the equator at sea level, and delete all bad equations. —Preceding unsigned comment added by 216.64.167.250 (talk) 18:13, 28 January 2009 (UTC)

(Add new sections at the bottom, please, by clicking the "new section" button.)
True that the earth's circumference is not 6378137 meters. Its radius, though, is widely reputed to be about that, as the article says. —Tamfang (talk) 07:10, 6 February 2009 (UTC)

## infuence of earth rotation on the direction of water vortex

earth rotates in counter clockwise direction.how does it affect the direction of wind and in turn affecting the direction of vortex in water.how does the winds move from equator to the poles. 210.212.244.133 (talk) 16:13, 3 March 2009 (UTC)

See Coriolis effects in meteorology. —Tamfang (talk) 05:35, 4 March 2009 (UTC)

## Earth's rotation in 24 hours

The Earth's Equatorial circumference is 24901.5 miles where 1 degree of geographical separation equates to 69.17 miles.That 69.17 miles also equates to 4 minutes of clock time so that the Earth rotates a full 24901.5 miles in 24 hours exactly.

http://www.ncgia.ucsb.edu/education/curricula/giscc/units/u014/tables/table02.html

The rapid transition from daylight to darkness at the Equator is due to the lower latitude within the intertropical zone and thus, sun sets on the horizon along a line close to the vertical which, in turn, makes that transition very short. --Fev 20:36, 20 September 2015 (UTC)

This formal proof using rotational cause,daylight/darkness transitional effect and the table of distances and time values in support obliterates the poor line of reasoning which leads to the 'sidereal time' value,a value cannot explain the daylight/darkness transition effect nor can it link in with the values for planetary circumference at different latitudes.Oriel36 (talk) 16:27, 10 July 2009 (UTC)

Please read the talk page guidelines. A talk page is only for suggested improvements to its article. You have not made any suggestion. Furthermore, your personal view is not allowed on Wikipedia unless you can provide a reliable source which makes the same argument. Your personal arguments are considered original research which is not allowed on Wikipedia. I suspect that you want all reference to Earth's rotation relative to the fixed stars, its sidereal/stellar rotation, removed from the article, or at least noted that it is wrong. That cannot happen because Wikipedia only repeats what is written in the secondary literature, which in this case is adequately referenced. It does not pass judgement on whether it is right or wrong. See Wikipedia's five pillars and What Wikipedia is not. Earth's rotation relative to the Sun, which you apparently prefer, is already in the article. — Joe Kress (talk) 19:41, 10 July 2009 (UTC)

This is clearly incorrect,the suggestion is in title that the Earth rotates in 24 hours with the historical table of values which clearly state the division of the Earth into 360 degree parts organised around its rotational characteristics where 1 degree of geographical separation equates to 4 minutes of clock time and 24 hours and 360 degrees in total.Because these values are crucial to the correct fact for daily rotation,I am compelled to put forward the tables again which link planetary shape and dynamics together -

http://www.ncgia.ucsb.edu/education/curricula/giscc/units/u014/tables/table02.html

The effect is also widely known where the transition from daylight to darkness,due to daily rotation,varies from rapid at the Equator to relatively slow towards the geographical North and South Poles therefore any objection or appeal to 'original research' must be considered disingenuous with the effect and cause of this phenomenon.The latitudinal correlation between time and distance explains the observed effect through the historical and technical details surrounding clocks,longitude and planetary dynamics and geometry.Depending on the level at which readers approaches this topic,here are two excellent websites -

http://www.grand-illusions.com/articles/longitude/page04.shtml

The 'sidereal time' value cannot explain the observed effect and it is foolish even to consider trying with the latitudinal values which represent rotational speeds and determine that the Earth rotates at its Equatorial circumference in 69.17 miles every 4 minutes and 24 901.5 miles in 24 hours.Oriel36 (talk) 21:15, 10 July 2009 (UTC)

I will not continue this discussion unless you state the specific words you want added to or removed from the article. — Joe Kress (talk) 04:49, 11 July 2009 (UTC)
grand-illusions.com is a toy shop, not a science site. Does its summary of the Longitude Problem even mention the equation of time? —Tamfang (talk) 19:19, 15 July 2009 (UTC)

The three basic planetary facts of shape,rotation and the length of time it takes the planet to turn once are bound together in that incontrovertible fact that the Earth turns through 360 degrees in 24 hours.A person who uses the table of values which determine the distance through 1 degree of planetary geometry/geography and also the latitudinal rotational speed for 4 minutes can be satisfied with the reason why transition from daylight to darkness,due to overall planetary rotation,is quicker at the Equator and less so at the poles but will also develop a distinct antipathy towards the 'sidereal time' value in the process.

I am well aware of the domino effect which distinguishes the correct 24 hour value from the alternative false value posited for daily rotation through 360 degrees in all areas of study which focus on time and planetary dynamics however,in a non confrontational spirit,I appeal to contributors to give the simple cause and effect due to the Earth's rotation more thought in order to correct this serious breach of reasoning which leads to the 'sidereal time' value.Oriel36 (talk) 07:03, 11 July 2009 (UTC)

See Twilight#Length: the time during which the Sun is below the horizon, but high enough to light up the sky, is shorter at the Equator because the apparent motion of the Sun is near perpendicular to the horizon there; not because the Equator moves faster. The speed of the Sun's apparent motion in the sky is the same at every latitude. — Apart from that, I don't see what you're getting at, other than that you apparently have an unshakable belief that rotation of Earth is the sole contributor to the apparent motion of the Sun. That assumption is useful for the measurement of geographic longitude, but untenable for extrasolar astronomy. —Tamfang (talk) 22:23, 13 July 2009 (UTC)

You are literally trying to disprove that the different latitudinal rotational speeds of the Earth do not influence rapid transition from daylight to darkness at the Equator and slower towards the geographical poles.It is daily rotation which causes the transition from daylight to darkness while the spherical characteristics of a rotating Earth determine how twilight is experienced at different latitudes,to believe otherwise is truly remarkable.It is that twilight effect and the table of values which determines,without question,that the Earth's rotation through 360 degrees is 24 hours and until you find a way to explain daylight/darkness transition using the 23 hour 56 minute 04 second value for rotation through 360 degrees in tandem with the 24901.5 mile Equatorial circumference,you will have to consider that 'sidereal time' value and the reasoning behind it as invalid.The 'sidereal time' value and the reasoning behind it is bogus and that represents the clearest description of a serious problem.Oriel36 (talk) 21:39, 14 July 2009 (UTC)

Are you aware that rotation is not the only movement, that Earth as a whole also moves around the sun? —Tamfang (talk) 05:14, 15 July 2009 (UTC)

The Earth's rotation is an independent motion and its effects can be considered independently of orbital motion,one of the effects of daily rotation is that it turns from daylight to darkness and the twilight transition at different latitudes is faster or slower as a consequence of the shape of the rotating Earth.There are definite speeds for each latitude with a maximum speed of 69.17 miles every 4 minutes at the Equator and turning the entire 24901.5 mile circumference in 24 hours.The technical reasons which determine that the Earth turns once in 24 hours are contained in the history of longitude whereas the 'sidereal time' value has a beginning with John Flamsteed and is extremely crude,it certainly cannot explain the twilight effect at different latitudes nor can it represent the shape and size of the planet as the 24 hour value can.In case you do not get the point,if children presently come to the main Wiki article looking for information on planetary shape and rotation,they will receive the wrong answer for both,that is not an opinion but a geometric certainty.Oriel36 (talk) 05:53, 15 July 2009 (UTC)

Both motions affect the timing of daylight, so no, they cannot be considered independently. (Without some motion other than simple rotation, there would be no seasonal variation in daylight and no analemma.) And no, the duration of twilight has nothing to do with speed of rotation; if the world were flat, the duration of twilight would still depend on the "latitude", i.e. the angle between the surface and the axis of rotation.
Are you attached to the solar day merely because it's older? Are you aware that it is less constant (over a year) than the sidereal day? —Tamfang (talk) 19:13, 15 July 2009 (UTC)

The values in the following table reflect the shape and rotational characteristics of the planet with the dynamical effects of not only the day and night cycle but the latitudinal differences in the transition from daylight to darkness which reflect that the Earth is a rotating sphere.You must provide an alternative set of values to disprove what the following table determines in respect to cause and effect of a rotating Earth for opinions without values are no longer accepted as a response - http://www.ncgia.ucsb.edu/education/curricula/giscc/units/u014/tables/table02.html . Those values determine that the Earth rotates through its full 24901.5 mile Equatorial circumference in 24 hours or a full 360 degree rotation in 24 hours.Oriel36 (talk) 19:58, 15 July 2009 (UTC)

If the linear speed of rotation is not the cause, then a different set of values for that speed will not account better for the effect. I have already seen the table you mention; you may post the link a fourth and fifth time, if you like, without persuading me that it is relevant. It's not just the data that count, it's how you apply them.
On second thought, yours is not a completely silly way to look at the matter. Twilight is a band of (practically) constant width behind the terminator; this width does represent a greater angle of longitude, and thus a longer time, at higher latitudes — but the relation of that duration to the rotational speed is transcendental, not inverse linear as you suppose. —Tamfang (talk) 21:29, 15 July 2009 (UTC)

The Earth's shape and rotation exist as one of the most fundamental facts which children worldwide will reference through Wikipedia and the only acceptable values are in that table representing speed,distance and 4 minutes of clock time which ultimately translate into the full facts that the Earth is a rotating sphere and takes 24 hours to rotate through its full Equatorial circumference of 24901.5 miles.Your personal opinions are worthless without the values which express the major planetary facts which are both simple and understandable in terms of cause and effect.The bogus 'sidereal time' value cannot hope to explain the effect of the day and night cycle and the latitudinal specifics of twilight transition as a location rotates into the orbital shadow of the planet at varying speeds.Oriel36 (talk) 22:23, 15 July 2009 (UTC)

Earth is not a sphere (it's oblate and bumpy), and it does not take 24 hours to make a full rotation, although that is a useful fiction for purposes of the Longitude Problem. Your objection to sidereal time is in the ignorant minority. Have you LOOKED at the illustration whose caption begins "On a prograde planet"? Have you READ that caption? Do you understand it well enough to paraphrase it? Do you see how it's relevant to the difference between solar and sidereal time? If you think it contains either a fallacy or a factual error, can you say what's wrong WITHOUT reminding us of the length of the Equator (which is completely irrelevant here; your argument would be no more nor less valid if it were 24 miles or 26 million miles) or linking to a toy shop's simplified summary of the Longitude Problem? Can you account for the equation of time? —Tamfang (talk) 05:45, 16 July 2009 (UTC)

The proof for daily rotation in 24 hours is simple,effective and mathematically incontrovertible requiring only basic arithmetic to attain the facts for planetary shape and rotational characteristics from the table of values and the effect of daylight to darkness transition at different latitudes. http://www.ncgia.ucsb.edu/education/curricula/giscc/units/u014/tables/table02.html . A teacher standing before students explains that daily rotation causes the day/night cycle with a rapid transition from daylight to darkness at the Equator and longer and longer twilight experienced at higher latitudes as rotational speeds diminish towards the geographical poles.There is no point responding if you cannot supply values which contradict the 24 hour value for rotation through 360 degrees and I know you cannot.The idea is for people to enjoy the cause and effect with the certainty of the values which support rotation in 24 hours.Oriel36 (talk) 20:29, 16 July 2009 (UTC)

A 24-hour day-cycle would imply 24-hour rotation if rotation were the only thing affecting the day-cycle, but it is not (see Copernicus). Your favorite table says absolutely nothing about rotation, so citing it casts doubt on your understanding. — If you want your reactionary heresy to be taken at all seriously, you might consider answering (or at least acknowledging) the questions in my previous entry. —Tamfang (talk) 05:21, 17 July 2009 (UTC)
Checking the numbers, I see that that table shows oblateness. —Tamfang (talk) 22:39, 17 July 2009 (UTC)

Check the numbers for the radius in the article and you get an Equatorial circumference of 40,075 km from a radius of 6378137.0 meters.Divide the circumference by 360 degrees and the value is 111.32 km per degree or 1669.8 miles every 15 degrees.The article comes out with false arithmetic of 1,674.4 km per 15 degrees of rotation with a trainwreck Equatorial circumference of 40,186 km for 360 degrees of rotation.Where those who propose the 'sidereal time' value for rotation through 360 degrees are going to put the excess 111km Equatorial geography is anyone's guess but this is a serious matter and needs a thorough review with the specifics of cause and effect along with latitudinal speeds as a guide.Oriel36 (talk) 17:58, 18 July 2009 (UTC)

Oriel36 has finally mentioned something that may require clarification in the article. The article's equatorial speed of 1674.4 km/h uses a sidereal hour, not a solar hour. But earthly speeds usually use the solar hour. Multiplying 1674.4 km/sidereal hour by 1.002738 sidereal hour/solar hour yields 1679.0 km/solar hour, not 1669.8. However, I cannot find 1679 km/h mentioned anywhere in the first few pages of a Google search. But I find several references to 1674 km/h, including this discussion that highlights its use of the sidereal day, even though the writer notes that the difference is "probably important only to the truly pedantic." Thus the quandary: Should we mention an equatorial speed that has no support in addition to the well known sidereal value, or simply note that 1674.4 km/h uses a sidereal hour? — Joe Kress (talk) 03:42, 19 July 2009 (UTC)
We should divide 1674.4 by the factor 1.002738 to obtain 1669.8, which can be found in many sources. However, the synodic surface speed is not constant throughout the year. If we add information on it, we should indicate a range (will be close to 1669.4 to 1670.1). −Woodstone (talk) 05:52, 19 July 2009 (UTC)

It is the geography of the Earth that maintains integrity here where the Equatorial circumference of 40,075 km divided by 360 degrees equates to 111.32 km per degree therefore the Earth rotates 1669.8 km per 15 degrees of rotation and 40,075 km through 360 degrees.The 'sidereal time' 1,674.4 km value for 15 degrees does not reflect the 360 degree Equatorial circumference distance and the geography of the planet let alone the speed at the Equator per hour.Introducing a blizzard of different time periods obscures the simple and effective fact that the transition from daylight to darkness is rapid at the Equator and becomes longer towards the geographical poles as the rotational speeds diminish with latitude.Those values which express 1 degree of planetary geography,4 minutes of clock time and organised around the rotational characteristics of the Earth renders invalid the entire article on the Earth's rotation .As it presently stands,the article on the Earth's rotation serves nobody and especially not children who wish a clear explanation for the cause of the day and night cycle and people who travel and experience the variations in twilight length as they move between latitudes.This is a sign-out comment.Oriel36 (talk) 07:14, 19 July 2009 (UTC)

Woodstone is correct—the erroneous figure is 1669.8 km/h, the same value Oriel36 and the many sites Woodstone found state. It is derived by dividing Earth's circumference (2π×6378137 m = 40075017 m = 40075.017 km) by 24 hours, yielding 1669.792 km/h. The common error here is assuming that Earth rotates once in 24 solar hours. Because Earth moves along its orbit while it rotates, it must rotate slightly more than once before the mean Sun passes overhead again. An easy way of correcting this is to multiply Earth's circumference by 1.002737812, the number of sidereal days in a solar day, meaning that a point on Earth's equator must move 40075.017 km × 1.002737812 = 40,184.735 km in 24 solar hours. This recognizes that 1669.792 km/h actually uses a sidereal hour, not a solar hour. Hence Earth's equatorial speed is 1.002737812×1669.792 km/sidereal hour = 1674.364 km/solar hour, which can be approximated as 1674.4 km/h or 1674 km/h, the other figures commonly quoted.
A more correct derivation starts with Earth's angular speed, 7.29211510 × 10−5 rad/s, given on the IERS page of useful constants cited in the article. The "second" here is an SI second, that is, a second of mean solar time. The rate of Earth's rotation is much more uniform than the time it takes for the true sun to pass overhead, so the mean solar second is more correct that a second of true solar time. Multiply by (180°/π rad)×(86400 s/24 h), yielding 15.04106708°/h. This is slightly more than 15°/h obtained by assuming that Earth rotates 360° in one mean solar day. Both figures are correct in their own way because "360°" in astronomy does not have the same meaning as it does in geometry. In astronomy it means returning to the same point in time, regardless of what that time scale may be. In this case, 1669.8 km/h uses the sidereal hour, whereas the figure that should be used with a solar hour is 1674.4 km/h. — Joe Kress (talk) 09:27, 19 July 2009 (UTC)
Thanks for checking the numbers! I hadn't bothered because Oriel36's fundamental premise (that rotation is the sole cause of the day cycle) is clearly wrong. —Tamfang (talk) 21:43, 19 July 2009 (UTC)

Absolutely not !,the Earth's Equatorial circumference of 40,075 km divided by 360 degrees yields 111.32 km per degree and 1669.8 km for 15 degrees.As rotation through 15 degrees is a valid statement and that value is 1669.8 km with a full 360 degree rotation giving the total Equatorial circumference of 40,075 km,any other value for 15 degrees does not correlate with planetary dimensions of circumference,radius and Equatorial speed.The values which determine the dimensional facts are organised around the Earth rotational characteristics and if you determine that the Earth rotates 1674.4 km through 15 degrees you end up with a nonsensical Equatorial circumference and planetary radius.Rotation of 1669.8 km per 15 degrees of planetary geography is a valid statement,likewise the fact that 1 hour corresponds to 15 degrees of planetary geometry as known through the longitude problem, so denying the basic fact that the Earth rotates through 360 degrees in 24 hours with different latitudes rotating at different speeds,due to the spherical shape of the Earth,is basically denying the entire history of planetary and timekeeping astronomy.What do you propose to do ? - make rotation through 15 degrees or 360 degrees an invalid statement for there are precise values for both at the Equator ,the former yields 1669.8 km and the latter amounts to a total 40,075 km.Oriel36 (talk) 12:27, 19 July 2009 (UTC)

I, for one, remain unmoved by your ability to divide the length of the equator by 24 and 360, and unrepentant in my preference for post-Copernican astronomy over pre-Copernican. —Tamfang (talk) 03:17, 15 April 2010 (UTC)

## Angle of rotation

Could the angle of rotation in the picutre be changed pleaseHpurcell (talk) 08:46, 17 November 2009 (UTC)

Please clarify. Do you object to the size of the angle or to its direction? The size is much larger than it is in reality for clarity. The direction is as viewed from the North star. — Joe Kress (talk) 21:01, 17 November 2009 (UTC)

## Origin Section is wrong and written poorly!=

I usually don't do any unilateral editing, but the section on the origin was written so poorly and the explanation was flat-out wrong that I had to at least fix it somewhat. As my cite shows, the original rotation does not have to do with any initial external supernovae or shock wave or anything like this--it is a property of a inhomogeneous dust cloud. Feel free to change anything, but please cite your work if you do. --68.195.44.36 (talk) 05:38, 23 March 2010 (UTC)

## variation of day length

User:Jc3s5h asked (in an edit summary),

Short of writing a bunch of computer software myself, where can I find the maximum deviation between actual and mean solar days?

Well, what's the maximum derivative of the equation of time? —Tamfang (talk) 23:22, 11 April 2010 (UTC)

Now answered in the article. A related integral is ΔT, a parabola that is the integral of the rate of increase in the length of the mean solar day, which is linear. Integration of the very small rate of 1.7 ms/day/cy produces the very large change in ΔT of 31 s/cy2, or conversely, the rate is the derivative of ΔT. — Joe Kress (talk) 05:45, 12 April 2010 (UTC)

The article states: "The true solar day tends to be longer near perihelion when the Sun apparently moves along the ecliptic through a greater angle than usual, taking about 10 seconds longer to do so. Conversely, it is about 10 seconds shorter near aphelion. It is about 20 seconds longer near a solstice when the projection of the Sun's apparent movement along the ecliptic onto the celestial equator causes the Sun to move through a greater angle than usual. Conversely, near an equinox the projection onto the equator is shorter by about 20 seconds." If someone has done the calculation, I think it would be useful to show the eccentricity and obliquity components of the longer or shorter true solar day for selective dates, perhaps for the first day of each month; e.g., for January 1: True Solar Day: +29 seconds -- Eccentricity Component: +10 seconds; Obliquity Component: +19 seconds Rodneysmall (talk) 02:45, 28 November 2010 (UTC)

I do not know of any source which plots the components separately. However, it can be done if the formula for the equation of time is given in a differentiable form. Unfortunately, neither component of the canonical form given in the equation of time article is differentialble. Instead, both components must be replaced by their series expansions. The equation of time article does give the largest term of both series. The series expression which replaces the true anomaly is called the equation of the center. The first three terms of both series are given by Jean Meeus in Mathematical astronomy morsels page 341. — Joe Kress (talk) 06:05, 28 November 2010 (UTC)

Thanks, Joe, I guess this is an even more complicated subject than I thought. However, looking at a couple of equation of time/length of solar day tables for early January (perihelion) and early July (aphelion), it appears that the maximum eccentricity component is more like 8.5 (not 10) seconds and the maximum obliquity component is more like 21.5 (not 20) seconds. Rodneysmall (talk) 02:42, 29 November 2010 (UTC)

## Significant Figures

Are twenty digits really necessary everywhere? That can't be real precision.--137.112.129.166 (talk) 07:30, 13 April 2010 (UTC)

I checked the references for a few of the numbers, and the precision was indeed real. Feel free to check all of them yourself; it's always good to have another pair of eyes to see that things were copied correctly. And there are only about 14 significant figures, not 20. Jc3s5h (talk) 15:45, 13 April 2010 (UTC)
The figures (14–16 digits) are those provided by the IERS, the international agency responsible for disseminating this information. The associated precision of about 1×10–15 is that typical of modern atomic clocks. — Joe Kress (talk) 18:51, 13 April 2010 (UTC)

## Other more subtle effects?

I see that the difference between the overly-simple sidereal time and a correction for precession of the orbit is well covered here and in other articles. But it also says that this "stellar time" is synonomous with inertial rotation. But I'm wondering about more subtle effects such as the sun's orbit in the galaxy, the galaxy's rotational motion within the dynamics of the local group, etc. 1 rotation every 250 million years would affect k' by 4×109 which is well within the 17 decimal places it is known to.

So I'm wondering if the article is sloppy in wording and the stellar time is really the measurement against an inertial non-rotating frame, including all effects (of which the precssion of the V.eq. is the largest component after the orbit of the earth), or the stellar time accounts for the v.eq. only and is not in fact the total of rotation components.

Długosz (talk) 22:58, 22 April 2010 (UTC)

Please define k' and v.eq. Earth's inertial rotation is affected by seasonal, decadal and longer variations, which are subtle effects only briefly mentioned in the article. The seasonal and decadal variations together exceed 2×107 of a day, which swamp any galaxy or local group effects. — Joe Kress (talk) 01:14, 24 April 2010 (UTC)
From context, v.eq. is apparently the vernal equinox, but k' is a problem. It might be related to the Gaussian gravitational constant, which is usually symbolized by k, but that is only defined to 10 significant digits (0.01720209895). — Joe Kress (talk) 08:03, 25 April 2010 (UTC)
According to the reference 6 the stellar day is derived from k', which is "Ratio mean solar day/stellar day". The reference claims it is consistent with the definition of the nominal Earth angular velocity ΩN. ΩN is the reference angular velocity corresponding to the epoch 1820. There is a very similar but not identical value in Aoki et al. on page 361. Jc3s5h (talk) 08:53, 25 April 2010 (UTC)

## Image clarification/concern

File:AxialTiltObliquity.png is a nice diagram illustrating all relative orientations and directions of the various motions. However (prompted in part by a Science Reference-Desk reader question), the "Orbit direction" vector is ambiguous because we do not know the perspective from which the diagram is made (from "inside" the orbit vs from afar looking in towards the sun). One of those is correct, one of those is not (would give the wrong Orbit direction direction). My addition to the caption clarifying that issue, in accord with the image's own description page statement "Earth is shown as viewed from the Sun; the orbit direction is counter-clockwise (to the left)" was reverted with comment "View is actually from the direction that is perpendicular to the Earth's axis and lies in the plane of Earth's orbit." and reverter recommended bringing here to figure out how to procede (nuke image vs improve caption vs ...). I think it's a good image for tying together multiple topics but needs a clear statement about the perspective. What's a good wording for that? DMacks (talk) 15:16, 31 August 2010 (UTC)

After thinking about it and making some drawings, yes, indeed, the view is from the Sun, but on the day of the March equinox. On any other day, the angle between the normal to the plane of the earth's orbit and the axis of Earth's rotation will appear different, from the Sun. For example, on the day of the January or June solstice, the axis of rotation will appear to coincide with the normal to the orbital plane, from the point of view of the Sun. I'm not sure how to express that concisely in the caption. Jc3s5h (talk) 16:39, 31 August 2010 (UTC)
I had assumed that your concern was that the POV does not precisely lie in the plane of the ecliptic. Is that not the case? I would think that it is close enough to say, "viewed from the sun"-- ToET 17:28, 31 August 2010 (UTC)
My concern is not whether the point of view is precisely in the plane of the ecliptic. I think saying "viewed from the Sun" is close enough. The problem is that if we don't say what day the view is valid on (the day of the March equinox) someone might think the direction of the axis of rotation constantly changes so that the angle between it and the normal to the ecliptic as viewed from the Sun is always about 23 degrees. In other words, the precession of the equnoxes goes through a cycle every year instead of every 23,000 years or so. Jc3s5h (talk) 17:34, 31 August 2010 (UTC)
I appended "... as viewed from the Sun during the vernal equinox" to the caption. -- ToET 05:39, 1 September 2010 (UTC)
Jc3s5h's description is better. The March equinox is vernal only in the Northern Hemisphere. DOwenWilliams (talk) 20:29, 5 September 2010 (UTC) David Williams

## TV "earths" often rotate the wrong way

Why is it that, when images of the earth are shown on TV, they are very often rotating in the wrong direction? Does nobody in the TV business know which way the earth rotates, or can't they figure it out from the way the sun moves across the sky?

DOwenWilliams (talk) 18:32, 1 September 2010 (UTC) David Williams

Are there particular examples you can think of? Note that the earth, when viewed from a non-retrograde, less than geosynchronous orbit, would appear to "rotate backwards". -- ToET 01:35, 2 September 2010 (UTC)
True, but such a close-up view would show only a smallish part of the earth. On TV, a full hemisphere of the earth is often shown, rotating the wrong way. DOwenWilliams (talk) 20:37, 5 September 2010 (UTC) David Williams
One major TV news department made such an animation for a special show about (i think) the Space Shuttle, and kept it in their main titles for years until they got tired of being told that it was turning backward. —Tamfang (talk) 18:26, 3 September 2010 (UTC)
A couple of nights ago, on CBC Television (I'm in Canada), the closing credits for the Ron James Show showed the earth turning backwards. Immediately afterward, the opening credits for the Rick Mercer Report also showed the earth, also turning the wrong way.
A year or so ago, I sent an e-mail to the producers of The Hour, which is CBC TV's late-night talk show, pointing out that they showed the earth rotating in reverse. The next time I saw the show, the problem had been fixed. Complaining can produce results. Whether it teaches lessons is another matter...
In shopping malls around here there are screens that show news summaries and the like, along with a lot of advertising for the stores in the mall. Many of the introductions to the news segments show the earth, almost always turning the wrong way. I don't know who generates the programming for these screens.
I'm sure I'll see more examples soon.
DOwenWilliams (talk) 20:19, 5 September 2010 (UTC) David Williams
Although I've never seen Earth rotating backwards, I have seen several rotating Earths without Antarctica. Their animators apparently used an outline world map that excluded Antarctica, such as a Mercator projection between 60°S and 85°N, and wrapped it around a globe, causing South America to almost reach the South Pole and Greenland to be too close to the North Pole. — Joe Kress (talk) 03:49, 6 September 2010 (UTC)
The rotating Earth that appears at the top of the "Article" page of this discussion does a pretty dreadful job of depicting Antarctica. There's just a white cap covering the South Pole and surrounding area. There's no trace of the peninsula that points northward toward South America, nor of other major features that exist around the coast of the real continent.
Oh well.... Terra incognita, I guess. DOwenWilliams (talk) 00:41, 7 September 2010 (UTC) David Williams
Could floating pack ice disguise the peninsula? —Tamfang (talk) 07:24, 8 September 2010 (UTC)
Not according to my trusty globe, which shows the extents of ice cover in summer and winter. The peninsula extends well outside the Antarctic Circle, almost to Cape Horn. There's no persistent ice there.
Actually, I have the impression that the rotation animation was made from data that did not include anything much further south than South America. The white area is far too big. DOwenWilliams (talk) 14:41, 8 September 2010 (UTC) David Williams
An example of a rotating Earth without Antarctica is on Wikipedia Commons as File:Rotating earth (large).gif. Indeed, even the southern tip of South America is missing. This distorts the rest of the Earth, causing South America to be a small continent totally within the Southern Hemisphere, and causing the equator to appear to pass through Cuba and northern India. — Joe Kress (talk) 07:07, 1 October 2010 (UTC)

## Coriolis effect on golf balls

I did a quick calculation of the effect of the earth's rotation on a golf ball that is driven a couple of hundred metres, staying in flight for ten seconds or so. In temperate latitudes, I think the ball will land a few centimetres from the point where it would have landed if the earth were not rotating. If the ball were initially exactly on target to go into the hole, the Coriolis effect would make it miss.

Of course, the effect would be zero at the equator, and in opposite directions in the two hemispheres. This suggests that maybe golfers who have practiced in the Northern Hemisphere might be at a slight disadvantage if they play in the Southern Hemisphere, and vice versa. The effect would be very small, but it might show up in a statistical analysis of a large number of shots.

Has anyone heard of this being done?

DOwenWilliams (talk) 23:14, 7 September 2010 (UTC) David Williams

It has an effect on ridiculously large cannons. See the Paris Gun, with a range of 120 kilometers.--RaptorHunter (talk) 19:45, 27 March 2011 (UTC)

## Obliquity vs Inclination

I just got through rewriting the reference to the equation of time. Although true solar time is related to the equation of time it is not the result of the derivative operator from calculus. Both are dependent on changes in the Earth's orbit. Obliquity vs inclination is a little tricky since they are interrelated. One refers to the inclination of the Earth's orbit but this is relative to the geocentric reference frame and the celestial equator. Similarly, the tilt of the Earth is relative to the fixed stars and varies over time. So for consistency I switched to the orbital term. Note that although the reference to the equation of time refers changes in the obliquity it was left intact. It's just point of view.

The obliquity has an effect on true solar time and the equation of time since it affects the meridian position of the Sun but the length of the solar day as a whole would not be affected by this. Changes in the speed of the Earth's rotation over long periods of time may have more of an effect. --Jbergquist (talk) 00:52, 15 February 2011 (UTC)

## First section, "Rotation period"

This material very much duplicates what is in the article Solar time. And this material also belongs to this other article! That the orbit of the Earth around the Sun is eccentric and that the plane of this orbit (the ecliptic plane) is inclined to the equatorial plane really has nothing to do with the Earth rotation as such! But precession/nutation belongs here! (and should be extended!)

Stamcose (talk) 20:02, 9 June 2011 (UTC)

## Rotational phase

This article starts with section "Rotational period".

But it would be better to start with a section "Rotational phase" having as essential content a reference to Newcomb's formula which when used together with UTC gives rotational phase (and therefore also rotational rate) relative vernal equinox with a very good accuracy. And in case the absolutely highest accuracy possible is desired, the correction terms determined by International Earth Rotation and Reference Systems Service to UTC time for use in Newcomb's formula should be employed!

Newcomb's formula is central!

Stamcose (talk) 10:06, 19 June 2011 (UTC)

Newcomb's formula was used to give sidereal time as a function of UT1, or more commonly, was used in the reverse direction to find UT1 given sidereal time that had been found by observation of stars. But Newcomb's formula is no longer in use. See, for example this article by Capitaine et al.

## Rewrite to get a less complicated and more logical structure

I think this whole article gets a bit messy mainly because it start with rotation relative the Sun which is irregular because of the orbit of the Earth.

I think the order should be

1. Proper rotation is rotation relative the fixed stars/quasars which is very stable and constant. (Tidal friction is certainly there but is it observable? References! Possibly less then the spin variation due to the change of the moment of inertia from Earthquakes etc?)

2. Next minor variation (but still very small) comes from the use of the Vernal equinox as reference point, the Vernal equinox being affected by the precession/nutation . Here Newcomb's formula is central. UT1 is even directly defined from Newcomb's formula!

3. Next comes the much larger irregularities from the Earth orbit (non-zero inclination and eccentricity). But this is not really "Earth rotation", this is just a phenomenon coming from the use of the Sun as reference!

This logical structure would make the article much easier to read and understand!

Stamcose (talk) 18:41, 29 June 2011 (UTC)

Following an advice above I had a look at the German version of this article, "Erdrotation", that seems to have been written by a real expert! This is very much in line what I proposed! It also confirms my assumptions that spin rate change due to tidal friction is much less then the spin rate changes due to the variation of the moment of inertia!

It says:

Die Gezeitenreibung übt ein bremsendes Drehmoment auf die Erde aus, so dass die Tageslänge langsam, aber kontinuierlich zunimmt. In den modernen Messreihen wird dieser Effekt völlig von den oben beschriebenen Fluktuationen verdeckt. Da er sich über längere Zeiträume aber aufsummiert, lässt er sich mit Hilfe überlieferter antiker und mittelalterlicher astronomischer Beobachtungen bestimmen.

Stamcose (talk) 19:03, 29 June 2011 (UTC)

For a historical overview of the variable rotation of the Earth, and a summary of the current understanding, read TIME: From Earth Rotation to Atomic Physics by Dennis McCarthy and P. Kenneth Seidelmann, published by Wiley-VCH in 2009. The current theory is that there are two principal secular effects; lunar tides increase the length of day by 2.3 ms day-1 cy-1, while post glacial rebound of portions of the Earth's crust shortens the length of day by -0.6 ± 0.1 ms day-1 cy-1, so the net effect is 1.7 ms day-1 cy-1. Irregular effects are of similar magnitude, and "are attributed to the interactions of the Earth's mantle and the liquid core."
Also, although Newcomb suspected variations in the length of the day, irregularities in the observations available to him, combined with the limited accuracy of the clocks available in the 1800s, prevented him from including any allowance for that in his Tables of the Sun. Hence, UT1 is no longer defined by Newcomb's expression for the longitude of the fictitious mean Sun, and rather is defined by the implicit relationship
ERA = 2π(0.7790572732640 + 1.00273781191135448Tu) radians
where Tu = (Julian UT1 date - 2451545.0) (McCarthy & Seidelmann 2009, pp. 15–17, 62–64, 68–69, 76)
The Earth Rotation Angle is found by measuring the position of extra-galactic radio sources using Very Long Baseline Interferometry. See the article Universal time for further discussion. Jc3s5h (talk) 22:31, 29 June 2011 (UTC)

But this is precisely what I have said all the time!

MJD2000 starts at mid-night! MJD is therefore Julian UT1 date - 2451544.5 and your T is t-0.5 in formula

${\displaystyle 99.96779469\ +t\ \ 360.98564737\ +t^{2}\ \ 2.907\ 10^{-11}}$

Using T instead of t the constant gets

${\displaystyle {\frac {99.96779469+0.5\ 360.98564737}{360}}\ =\ 0.779057273}$!

and the linear term gets

${\displaystyle {\frac {360.98564737}{360}}\ =\ 1.002737909}$

The last decimals are 909 while you have 812

And yes, UT1 is defined through Newcomb's formula which is precisely

ERA = 2π(0.7790572732640 + 1.00273781191135448Tu) radians

if the quadratic term is ignored and the least significant decimals 909 are changed to 812

Why do you write:

"Hence, UT1 is no longer defined by Newcomb's expression for the longitude of the fictitious mean Sun, and rather is defined by the implicit relationship"

?

What I call Newcomb's formula and clearly define has nothing to do with any "fictitious mean Sun". There is a perfect agreement between "McCarthy & Seidelmann" and myself (except for the last 3 least significant decimals)

79.216.180.27 (talk) 10:26, 30 June 2011 (UTC)

You asked why I wrote "Hence, UT1 is no longer defined by Newcomb's expression for the longitude of the fictitious mean Sun, and rather is defined by the implicit relationship...." Simon Newcomb died in 1909. The earliest mention I can find of anything related to Earth Rotation Angle is "Determination of the motion of the pole, and comparison with astrometry" by B. Guinot in Royal Society (London), Philosophical Transactions, Series A, vol. 294, no. 1410, Jan. 14, 1980, p. 329-334. It uses the term "instantaneous ascension" for a concept similar to Earth Rotation Angle. Since 1980 is several decades after Newcomb's death, no expression based on concepts first published in 1980 should be called Newcomb's formula. You say that you define it as Newcomb's formula. I do not accept your authority to label it Newcomb's formula. Jc3s5h (talk) 13:55, 30 June 2011 (UTC)
Let me add that if you were to read the sources I provided you would learn that the definition I gave above was recommended by the International Astronomical Union in 2000 and has since been accepted throughout the world by timekeeping authorities. Since it is a definition rather than a measurement, it is perfectly accurate, and any expression that differs from it in the slightest way (such as the addition of a quadratic term) is not the definition. Jc3s5h (talk) 14:16, 30 June 2011 (UTC)

The "mean solar second" as chosen by Simon Newcomb (without access to atomic clocks) was accurately chosen. The "mean solar day" (86400 "mean solar seconds") was then the time unit to describe the Earth rotation through "Newcomb's formula" that again was very accurate.

Long after Newcomb's death the "UTC second" was chosen to be as close as possible to Newcomb's "mean solar second" and the UT1 time was directly defined by the Earth rotation angle (relative vernal equinox) through Newcomb's formula. This is all no revolution in concepts but an adaption of the Newcomb concepts to accurate atomic clocks.

As the UTC time is slightly biased to run faster then UT1 leap seconds are introduced from time to time to keep the difference between UT1 and UTC below 1 second.

That UTC time driven by the Earth rotation relative vernal equinox (i.e. UT1) still fits sunrise, noon, sunset is thanks to the well selected factors of Newcomb's formula to fit the "mean solar year"

You write: "no expression based on concepts first published in 1980 should be called Newcomb's formula"!

The International Astronomical Union just adapted the Newcomb standards to new hardware,i.e. atomic clocks. Newcomb is not around anymore but Newcomb's formula still lives and is extremely relevant for these concepts published 1980!

Is

TIME: From Earth Rotation to Atomic Physics by Dennis McCarthy and P. Kenneth Seidelmann, published by Wiley-VCH in 2009

saying something different?

Stamcose (talk) 21:30, 30 June 2011 (UTC)

Newcomb's work was very good and was used for many purposes until the Astronomical Almanac for the Year 1984. However, there were other formulas of the same form as Newcomb's that weren't bad either. Considering that several formulas with only slightly different coefficients exist from the 19th century, any change to the coefficients requires a change to the name. Also, the most recent formula is of a different form than Newcomb's. When I compare the expression for Greenwich Mean Sidereal Time printed in the Explanatory Supplement to the Ephemeris, printed in 1961 and based on Newcomb's Tables of the Sun to the Naval Observatory's Multi-Year Computer Almanac which is based on the latest conventions, the Newcomb-based formula is, at 00:00 UT January 1, 0.06 s fast in 1800, 0.02 s slow in 1900, 0.08 s slow in 2000, and 1.04 s slow in 2050.
By the way, what is the source for the formula you posted above? Jc3s5h (talk) 22:02, 30 June 2011 (UTC)

## Length of Day

The previous Wiki article *Length of Day* redirects to this article unconditionally. However, *Length of day* has a second meaning, namely "the length of the bright day as opposed to the dark night." This seems to be covered by the article *Daylight* now. Can someone more familiar with Wiki's formatting templates maybe insert the text "For other uses, see Daylight", please? Gulliveig (talk) 09:14, 6 July 2011 (UTC)

Done. Jc3s5h (talk) 14:04, 6 July 2011 (UTC)

## Too many solar time articles

Please see Wikipedia talk:WikiProject Time#Too many solar time articles Jc3s5h (talk) 17:34, 2 August 2011 (UTC)

## History of Lat/Long system ,the AM/PM cycles and the Earth's rotation

Extended content

The Earth's rotation once in 24 hours is derived from the conversion of natural noon AM/PM cycles to 24 hour AM/PM cycles of which there are 1461 such astronomical events enclosed in 4 orbital circuits of the Earth.The steady and constant progression of 24 hour days substitutes for constant rotation therefore there is no natural external reference for daily rotation as an independent motion no more than there is an external reference for the 24 hour average day,this is verified by all authorities from Christian Huygens to John Harrison,the two main contributors to civil timekeeping and the resolution of location on the planet using the Lat/Long system and the AM/PM cycles.http://www.youtube.com/watch?v=kDWHM00sZJc .The entire article on the Earth's rotation is unsuitable for students at any level.Gkell1 (talk) 19:50, 26 April 2012 (UTC)

The preceding is gibberish and anyone who edits the article on the basis of the preceding should anticipate adverse reaction. Jc3s5h (talk) 00:49, 27 April 2012 (UTC)

The astronomical equivalent of 2+2=4 is that the Earth turns 360 degrees in 24 hours,it is so technically and historically attested to that any alternative correlation amounts to 2+2=5 and at variance with common experience of the effects within a 24 hour day in step with one rotation of the planet.It is a serious dereliction of duty to knowingly propagate false information at this level as the 24 hour day/rotation is not a theory and does not lend itself to anything other than an expression of a fundamental fact.Gkell1 (talk) 20:00, 28 April 2012 (UTC)

False. You know it's false. You are a troll and if you put this trash in an article you will be treated as a vandal. This is your last warning. Jc3s5h (talk) 23:19, 28 April 2012 (UTC)
2+2=4 is a definition. That the day-length roughly coincides with the rotational period is an observation. The difference is vital. —Tamfang (talk) 22:58, 27 May 2012 (UTC)

Tread carefully,the insertion of rotational dynamics as a mechanism into the 'Plate Tectonics' topic came long after I proposed the mechanism linking the planet's spherical deviation with crustal motion/evolution and that entire subject is dependent on a maximum equatorial speed consistent with rotation once in 24 hours or 1037.5 miles/15 degrees per hour.The issue is far reaching for not only the topic itself but the manner of creative editing without attribution.Gkell1 (talk) 16:17, 29 April 2012 (UTC)

The image of stellar circumpolar motion in conjunction with daily rotation is an affront to astronomy - star trails indicate constant rotational alignment,nothing more or less.The primary reference for diurnal rotation is gauged against the Earth's orbital motion and these two motions combine to create the variations in the natural noon cycle which is referenced to the central Sun and out of which the average rotation across 4 orbital circuits is derived.It is not possible to isolate daily rotation using stellar circumpolar motion no matter how popular the ideology has become whether through the original error deduced using pendulum clocks (Flamsteed) or VLBI. Gkell1 (talk) 18:27, 11 June 2012 (UTC)

If the stars are rejected as a reference background (because their apparent motion conflicts with your definition of 'rotation' as one day-night cycle), how do you measure orbital motion? Or do you define it as that which occurs in one Julian calendar year? —Tamfang (talk) 23:13, 11 June 2012 (UTC)

One 24 hour day meshes with one 360 degree rotation of the Earth is not a definition but an experience in such a way that the expanded experience of this fact is set within the boundaries of 4 orbital circuits as 1461 rotations to the nearest rotation. The observation that the central Sun appears 1461 times in a 365/366 rotational format spread across 4 circuits obliterates the assertion that a circumpolar star returns 1465 times for the same period.The entire article is not fit for general readership and considering this is the primary experience between planetary dynamics and terrestrial effects,the lax way this is being handled is just as relevant as the technical details. Gkell1 (talk) 07:36, 12 June 2012 (UTC)

In science, unlike theology, a pre-existing theory does not "obliterate" a conflicting observation. These two observations together demonstrate that Earth's rotation is not the only thing that contributes to the apparent motion of the Sun. I asked you once before to demonstrate either that you understand this point or that it's false, and all you offer is tautology: 360°÷24=15° and 24×15°=360°, hurrah! —Tamfang (talk) 17:20, 12 June 2012 (UTC)
Elsewhere you make a big deal of the appearances of Sirius. Is Sirius trustworthy because it's not circumpolar? —Tamfang (talk) 17:59, 12 June 2012 (UTC)

## Tidal effects

In the newly-extended lead, I changed "tidal friction" to "tidal effects". As I understand it, friction as the water moves due to the bulge in the oceans caused (mostly) by the Moon's gravity is an essential component to the slowing, because the friction causes the bulge to be dragged slightly ahead of the Moon. The transfer of angular momentum from the Earth to the Moon is possible because the bulge is not exactly on the line from the center of the Earth to the center of the Moon. But the slowing is primarily a transfer of momentum and energy from the Earth to the Moon, rather than a dissipation of energy as the word "friction" implies. Jc3s5h (talk) 16:10, 10 August 2012 (UTC)

It occurs to me that due to the irregular distribution of the continents there is probably more tidal friction in one hemisphere of the Earth than the other. (I guess in the Northern hemisphere, as the continents stretch across the entire hemisphere.) Would this not tend to affect the direction of the Earth's axis, and if so would the effect be significant over a long enough period?86.152.31.240 (talk) 14:56, 8 June 2013 (UTC)

## definition of Siderial

I'm not too happy with the note that siderial is "arguably a misnomer". It asserts that "the dictionary definition of siderial" (as if there were only one dictionary, and only one definition) is the same as stellar. I doubt that's true. At any rate, there is no reference for it. I purpose to remove it after a reasonable interval. Rwflammang (talk) 22:00, 29 November 2012 (UTC)

## Coriolis?

The section now titled Empirical tests contains the sentence "Because of this Coriolis effect, falling bodies veer eastward from the vertical plumb line below their point of release." Is it correct to call this a Coriolis effect or does it have its own name? Does anyone know? The reason I don't think it's Coriolis is that this effect is at a maximum at the equator and disappears at the poles--precisely the reverse of Coriolis. (It is of course minute, which was why it was very hard to observe.)

There's a reference to Riccioli quoting this as an objection to the movement of the earth (objection B6 p70 of the cited text). But as with cannon ball argument (B17 p75) which credits Tycho Brahe, the falling object argument was used by Tycho: "Tycho Brahe maintained that this argument about the falling stone was unanswerable." (see Dreyer p356). I'm inclined to agree with Dreyer 2 pages earlier when he says, re Riciolli (abbreviating slightly) "It would be useless to set forward the arguments from the Scriptures against the movement of the earth in the 16th & 17th C; they are much the same as the Fathers of the Church used 1,000 years earlier in defence of the Babylonian system of the world" (though of course the whole style of argument is Aristotelian not biblical.) Chris55 (talk) 20:50, 4 October 2013 (UTC)

Yes, it's part of the Coriolis effect and has the special name Eötvös effect.−Woodstone (talk) 04:56, 5 October 2013 (UTC)
No, that's not it. That results from "eastbound or westbound velocity". This effect is due simply to something falling vertically from a height. Chris55 (talk) 08:18, 5 October 2013 (UTC)
It fits perfectly in the definition and formulas of the Coriolis force. The Coriolis force is perpendicular to the movement and to the Earth's axis and proportional to the sine of the angle between them. So something falling above the equator will veer East because of it. Something falling at higher latitude will veer East as well, but less. At the pole there is no effect. Reversely, something moving East along the equator, will drift upwards. At higher latitude it will veer up at an oblique angle to the surface, but straight from the Earth's axis. Both effects are known under the name Eötvös. −Woodstone (talk) 17:34, 5 October 2013 (UTC)
Ah, thank you. I could see there was a ${\displaystyle \cos \varphi }$ in the vector but was using the simplified explanation further on in the Coriolis effect article. I was thinking naively in terms of velocities, whereas I see it's actually an acceleration, and therefore ended up with a figure somewhat higher than in the article. Of course, in the 16th/17th century neither Tycho or Riccioli attempted any calculations; I presume Newton could have, though I don't know whether he did−or is that the point of the Hooke story? Chris55 (talk) 19:43, 5 October 2013 (UTC)

## Even some astronomers...

A recent edit and its corresponding comment betray a lack of understanding in the nature and cause of the paradigm shift from a geocentric to a heliocentric model in the Early Modern period. The offending comment was, One rather bad experimenter a century later does not count as "many". And Copernicus predated the telescope by 70 years.

The comment apparently refers to the author of Almagestum novum, the ninth chapter of which is a compilation of arguments written by many different astronomers for and against the heliocentric model. Chris55, who wrote the comment, seems to think that it is the opinion of only one astronomer, the author who compiled it. But the Almagestum novum was the standard astronomical textbook used by all astronomers of the time, including Newton. It was not the work of a lone eccentric but was representative of the views of the astronomical community. The jibe about the author's experimental competence does not seem germain, given that no superior experimentalist was able to demonstrate the existence of Coriolis effects before the 18th century.

Chris55 wants to emphasize the importance of Aristotelian physics and the Bible in inspiring those who disputed diurnal rotation of the earth. This view is problematic for several reasons.

• Aristotelian physics began to fall out of favor long before Copernicus and that fall was complete in the astronomical community 60 years after the publication of De revolutionibus, but this had no effect on the popularity of the various geostationary models. That means that Aristotelian physics can hardly be viewed as critical to geostationary models, even if geostationary models were critical to Aristotelian physics.
• Although astronomers found inspiration and some corroboration for their geostationary models in the Bible, the same was true of Copernicus, Kepler, and Galileo. Later widespread acceptance of geomobile models led to no corresponding rejection of the Bible. And so here too biblical interpretation can hardly be viewed as critical to geostationary models.

The reason for astronomers disputing geomobility had to do with the fact that there was, at the time, absolutely no observational evidence in its favor. The theoretical advantages of geomobility were entirely subjective before Kepler published his Rudolphine tables. Even then, it was not really apparent whether Kepler's model represented any kind of physical reality, or whether it was just a really cool mathematical device that just happened to give a calculational advantage over its competitors. When Newton provided a dynamical explanation of Kepler's model with his theory of gravitation, only then were the geostationary models abandoned. The diurnal rotation of the earth must be true since the heliocentric model was true. There was still no direct evidence of diurnal rotation, but using Newtonian mechanics, natural philosophers were able to calculate the magnitude of the rotational effects and see that they were very small indeed.

So the article has it stands now has the following problems.

• It assigns prominence to secondary issues in the geostationary-geomobile dispute (Aristotle and the Bible) while ignoring the primary issues, which were non-evidence and the obvious lack of expected Coriolis effects.
• It erroneously gives the impression (even some astronomers, it says) that most astronomers did, or should have, agreed with Copernicus. Although that is true today, it was not true in 1543, nor was it true one hundred years later.

Too bad it's not directly referenceable, but a real bogging tour de force showing the issues surrounding the paradigm shift, if not all its details, can be found here and in its eight sequels. Rwflammang (talk) 02:03, 7 October 2013 (UTC)

I'm glad that Rwflammang has revealed their true allegiance by the link in the last paragraph.
Unlike him/her, I didn't delete an opposing point of view, but tried to put it into context and even provided a proper citation. In fact, reading Graney's account of Riccioli, I'm reminded of nothing more than Carpenter's 100 proofs that the world is flat. Ok, I admit that's an order of magnitude worse, but the method of argument is very similar: quote an apparently "obvious" truth, assert that your opponent's position contradicts this truth, and move on to the next argument. At the end, weigh the arguments. Schofield writes: "Riccioli's anti-Copernican arguments from the motion of falling bodies were considered so futile, for a man of Riccioli's calibre, as to strongly suggest prevarication."
To do a proper experiment in science it's necessary to come up with an estimation, and preferably a calculation, of what the result will be. Riccioli doesn't attempt this: if he had, he would have realised that the effect is so small as to be utterly undetectable with the instruments then available.
This experiment was evidently Tycho Brahe's favourite refutation of the heliocentric position and it's more understandable that he couldn't do the maths. After all, at the time, Galileo hadn't proved the constant acceleration of falling bodies. (But Riccioli thought he'd disproved that too.) I wonder why Rwflammang uses Riccioli rather than Tycho Brahe as the support, even though he was recycling his arguments. Is it because he isn't so well known?
You say Aristotelianism was going out of fashion. I agree, but read Riccioli's arguments. e.g. He constantly refers to the idea that circular motion is the only 'natural' motion (see arguments A3, A49, B1 etc.) - totally Aristotelian and with no basis whatsoever. And that is only one example.
You deny there were advantages for astronomers before Kepler, but Christoph Clavius used the Prussian Tables of Erasmus Reinhold, which were based on Copernicus, to propose the Gregorian calendar in 1582.
I haven't attempted any estimation of what the balance between support and opposition is because I haven't yet found a list of the opposition astronomers in the 16th century. There were some such as Franciscus Patricius who accepted the rotation of the earth even though they denied the revolution of the earth about the sun. It's interesting to note that Ptolemy's estimate of the radius of the starry sphere was about 100 million miles, so the assumed speed of the stars must have been about 27m mph. I doubt anyone calculated that at the time though the problem was perhaps obvious. (Of course with current estimates the speed of the nearest star would be approaching 10,000 times the speed of light.) Chris55 (talk) 15:17, 7 October 2013 (UTC)
I'm glad that Chris55 have revealed their true allegiance by the link to Dreyer above. Could any writer other than Dreyer be more comically whiggish? (White, I suppose.) But "even" Dreyer had no illusions about the balance between support and opposition. He bemoans, "It is therefore not to be wondered at, that with the exception of the few men we have mentioned, nobody accepted the Copernican doctrine as true during the first half century after 1543, though everybody used the Prutenic tables". (Pardon my emphasis; I do not mean to shout.)
The point about "proper scientific experiments" is right as far as it goes, but then, experimental shortcomings were hardly a characteristic of one camp or the other in those days; they were characteristic of the age, which was still awaiting Newton. Not that any of that is relevant; these shortcomings are directly traceable neither to Aristotle nor to the Bible, so my objections still stand.
The point about Clavius' use of the Prutenic tables, however, is a very good one. I don't really know why he used them, but I'm not convinced that it was because they were over all more accurate. Certainly I will concede that they were no less accurate than the Alphonsine tables. My understanding, gathered by reading sundry sources over the decades, is that they were a wash; more accurate in some parts, less accurate in others. I'd like to know more details. I somehow doubt that calendar reform relies in any way on the more intricate motions of planets, just the relatively simple and direct motion of the sun and moon. It is hard for me to see why one world system should be preferable to the other for such purposes.
The point about Tycho vs. the Almagestum novum is also a good one. Why even mention the new Almagest? The best arguments in it are Tycho's! This is, of course, pointed out in the Almagest itself. The reason for citing the Almagest is twofold.
• The Almagest Chapter 9 was a compendium of all of the reasonable (or at least notable) debating points put forward by contemporary geomobile modelers and geostationary modelers. The fact that Tycho still dominated the argument a half century after his death is more notable than just mentioning him as one of even some astronomers, as some sort of outlier.
• The new Almagest is not merely Tycho's mouthpiece. It is a survey, the closest thing we have today of a consensus of the astronomical community at the time of its publishing, at the time shortly before the dissolution of the geostationary world system ushered in by Newton.
I do not object to including Tycho, but I do object to mentioning him as if he were some kind of crazy eccentric, who just couldn't convince himself (like all reasonable astronomers) to go along with Copernicus.
Rwflammang (talk) 00:43, 9 October 2013 (UTC)

You are both trying to rewrite history or airbrush out the real concerns which emerged when Copernicus developed arguments which resolved apparent retrograde motion and the daily return of the Sun using the Earth's motions rather than any motions attributed to the Sun or the other planets.The greatest difficulty was whether the system which predicts astronomical events and the relationship of celestial objects to each other could be used to prove the Earth moves.The short answer is that it doesn't even though the later empiricists in the late 17th century tried to prove it does and still do.Orion216 (talk) 07:35, 9 October 2013 (UTC)

No, we are not. And Coriolis forces are not motions of celestial objects. But neither of these points is relevant, since they do not pertain to my objections about the article as enumerated above. Rwflammang (talk) 02:50, 10 October 2013 (UTC)

## Criminal incompetence

The technical qualifiers for the erroneous notion that the Earth's rotation can be extracted directly from stellar circumpolar motion demonstrates to a 100% certainty that waking up to one 24 hour cycle is also waking up to another rotation of the planet with no mismatch or divergence between the AM/PM cycle and rotations. Despite the awful Wiki attempt to squeeze the planet's rotation into a 'geology project',without the correlation between one 24 hour cycle and one rotation there is absolutely no mandate to discuss cause and effect between planetary dynamics and terrestrial sciences.It is that serious and this topic requires serious people.Orion216 (talk) 07:27, 9 October 2013 (UTC)

And your proposal to improve the article is what exactly? Please feel free to respond when you are sober. Rwflammang (talk) 03:24, 10 October 2013 (UTC)

Improve !!!,the structure of the article is corrupt to the point of criminal incompetence insofar as the first things students should read is that the Earth turns once in 24 hours.The homocentric observation that a star returns to the same foreground reference in 23 hours 56 minutes 04 seconds is based on the average 24 hour day within the 356/365/365/366 day framework and cannot be used to explain much less prove constant daily rotation.The Lat/Long system in tandem with the 24 hour AM/PM system is the only acceptable framework for constant rotation where the planet turns at a rate of 15 degrees per hour and it is unconscionable that anyone would believe otherwise.Orion216 (talk) 06:16, 12 October 2013 (UTC)

As a matter of fact, it is very conscionable; get over it. What the length of a Julian year might have to do with a measure of the Earth's rotation rate, you leave obscure. I request a reference. Rwflammang (talk) 00:37, 13 October 2013 (UTC)

I am afraid you need an education rather than a reference and indeed so does the entire empirical community. The core 24 hour AM/PM system in tandem with the Lat/Long system is not based on the rotation of the Earth, it is based on the proportion of rotations to orbital circuits which turns out to be 1461 rotations to 4 orbital circuits to the nearest rotation.The 24 hour average day is extracted from those 1461 natural noon cycles where the average is transferred to constant rotation as an assertion and the specific reference was originally the apparent motion of Sirius along the ecliptic axis and nothing whatsoever to do with stellar circumpolar motion,something that originated with Flamsteed and the late 17th century equatorial coordinate system. I realize that discussing this material is like discussing the inner workings of a microchip to people who have never seen a computer so it is irritable for me in dealing with the sort of incompetence that wrote that article and then expects students to make sense of it.Orion216 (talk) 01:25, 13 October 2013 (UTC)

I have an education. I see no evidence that you have one. Sounds like a brainwashing is more what you have in mind, anyway. Good luck finding a reference for that! Per WP:FRINGE, your proposed changes will not be made. Rwflammang (talk) 00:49, 14 October 2013 (UTC)

The article on the Earth's rotation is written by intellectual charlatans with no appreciation whatsoever for the Lat/Long system and where it meshes with the 24 hour AM/PM system around the Earth's rotational and orbital characteristics.It is not compliant with the historical and technical details which create the 24 hour average from the 1461 natural noon cycles covering 4 orbital circuits,an equalizing system that does not include any stellar circumpolar components beloved of the 'solar vs sidereal' cult.The Earth does not turn once to the Sun in 24 hours nor does the homocentric observation that a star returns to any indiscriminate foreground reference constitute constant rotation through 360 degrees,two flawed perspectives that are used in tandem to create the mess seen in that article.I do not see a serious treatment of this topic and especially the incredible decision to squeeze planetary rotation into a subset of 'geology'Orion216 (talk) 13:48, 15 October 2013 (UTC)

## The tangential speed of Earth's rotation at a point on Earth

Under Angular speed there is comments with the "tangential speed of Earth's rotation at a point on Earth", but this is only the speed in respect to the poles, not in respect to tangential speed of fixed stellar or solar coordinates. — Preceding unsigned comment added by 98.95.17.73 (talk) 04:09, 18 December 2014 (UTC)

## The direction of the rotation

The article claims that the Earth moves from west to east. This sentence is redundant and means nothing. Here is my explanation.

Assume we are viewing the Earth on its side, not on either its poles. The north is on top of the circle we see On the most westerly visible point we mark a point X. The article says that the Earth moves counter-clockwise as viewed looking at the north pole. To achieve this, X would move from left to right. This is a case in which the statement in question is correct.

However, even if X moves leftwards, thereby moving out of site, then reappear on the right, it would still have moved from west to east. Therefore, I propose the deletion of the statement in question. The Average Wikipedian (talk) 09:07, 22 January 2015 (UTC)

## Would be nice to have concrete data on how fast Earth spun historically

Like some kind of graph with time on the x axis and day length on the y axis. Ideally it would cover the billions of years since the beginning of rotation to the present day, with major epochs marked. I've been scouring the internet for anything more than vagueness like "in the distant past, the Earth spun once every 5/6/8/14/20 hours", with no citation given nor any attempt to quantify just how far in the past we're talking about. Is the slowdown linear? Exponential? Wobbly? I would love to know :(

143.167.146.175 (talk) 14:46, 2 March 2015 (UTC)

Some data and a nice plot (on page 2) of what you are looking for exist in Williams (2000): "Geological constraints on the Precambrian history of Earth's rotation and the Moon's orbit". (Though the plot only contains accurate points for the last 600Myr and contains any points for the last 2Gyr). However, it is under AGU copyright so it can't presently be uploaded directly to this page.

--Bencbartlett (talk) 19:05, 29 June 2016 (UTC)

## Is there any proof the Earth rotates?

Is there any proof that the Earth rotates? What proof is there that the Earth isn't 100% fixed and everything else rotates around the Earth?

ZhuLien (talk) 12:23, 26 March 2015 (UTC) ZhuLien — Preceding unsigned comment added by 116.240.194.132 (talk)

### A short answer

The Foucault's Pendulum is a valid proof of the Earth's rotation and, besides, of the direction of this rotation (counterclock wise in the northern hemisphere and clockwise in the southern one). --Fev 20:58, 20 September 2015 (UTC)

## Earth's rotation 2,500 years ago

An editor recently added this text to the end of the first paragraph: “ though some researchers claim the slowdown is significantly greater - as much as 4-5 hours over the past 2,500 years”. The reference for this text is to an article about Jerry Mitrovica in Harvard Magazine which says this: “...ancient eclipse records extending back thousands of years from “Babylonian, Chinese, Arab, and Greek astronomers indicate that the earth’s rotation has slowed about four hours” in two and a half millennia, Mitrovica explains. ”

First, the four hours in the quotation has been rendered as 4--5 hours. More importantly, I think the editor has misunderstood the quotation. The claim is not that the day was 20 hours long in 500 BCE, but rather that the accumulated difference between the day as measured by the rotation of the Earth and the modern definition of 24 hours will amount to 4 hours when you get back to 500 BCE.

The accumulated difference between the rotation of the Earth and a clock which measures time uniformly is called Delta T. That Wikipedia article mentions that Delta T in 500 BCE is estimated at 4.75 hours. That might be the source of the editor's modification of 4 (from his source) to 4--5 hours. However, it renders the whole phrase unnecessary, since there is general agreement about the value of Delta T; it is not just the opinion of “some researchers“.

If there is no objection, I will remove the edit. John Sauter (talk) 04:48, 6 September 2016 (UTC)

I agree. In context, the added text seems to claim the day was only about 20 hours (72,000 SI seconds) long in 500 BCE, but the literature, including the 2004 Morrison and Stevenson paper cited in this article, indicate that 4 hours is the accumulated error, also known as ΔT. I went ahead and reverted the edit. Jc3s5h (talk) 13:42, 6 September 2016 (UTC)

## Long term variation

There is a new study, just published in the Proceedings of the Royal Society A by Hohenkerk, Morrisoson Stephenson et al. which has had some coverage in the popular media. Unfortunately, I am unable to pursue this right now, but a simple search of the news under "earth rotation slowing" turns up several reports. I would be like to be able to pick out a nice, clear, correct report which will be accessible to the public to add here. I would think that this is interesting enough that it deserves more than a single sentence. TomS TDotO (talk) 16:34, 7 December 2016 (UTC) TomS TDotO (talk) 16:34, 7 December 2016 (UTC)

Tom, this is a subject that has been researched for a long time. I'm sure the new report will be very thorough, but I think the article in Astronmy & Grophysics is accessible to the average Wiki reader. Isambard Kingdom (talk) 16:45, 7 December 2016 (UTC)
This seems to be worth a section here - if not worth an indeprendent article. More than just a cryptic sentence. TomS TDotO (talk) 02:28, 8 December 2016 (UTC)
Earth rotation is a deep subject, and it can be difficult to understand all the affects and effects. A really good book, which is not, for reason, cited in this article, is that by Munk and MacDonald: [1]. It is an oldish book (slightly older than me!), but it contains lots of interesting material and it is written very clearly. Isambard Kingdom (talk) 02:49, 8 December 2016 (UTC)