Talk:Day length fluctuations

Merger proposal
This article is being discussed for deletion because it seems that many other pages cover the same content. One of these is ΔT. On that page, there is discussion of the appropriateness of the name, which is a symbol that can represent many things. However, according to the Morrison & Stephenson reference in ΔT, this quantity is a measure of changes in the length of day. Why not solve the name problem and save this article at the same time - by merging ΔT into this article? RockMagnetist (talk) 17:21, 30 May 2012 (UTC)
 * I see several problems with this proposal.
 * First, ΔT and LOD are two different, but related, quantities. ΔT is a summation of the difference in the length of day from the present (or some other chosen epoch of reference) to a moment in the distant past or future.  To quote from the ΔT article: "the Earth's rate of rotation must be integrated to obtain time, which is Earth's angular position."
 * Second, the Changes in the length of day article is very much concerned with the short term measurement of the Earth's rotation (and other elements of the Earth's orientation); the ΔT article is concerned with the evaluation of ΔT over extended periods of time (which is really what you'd expect for a quantity that is generated by a long term summation.
 * Third, the Change in the length of day article is probably closer to the article on Universal Time or perhaps even to the article on the International Terrestrial Reference System than it is to ΔT.
 * SteveMcCluskey (talk) 17:46, 30 May 2012 (UTC)


 * In addition to what SteveMcClusky wrote, the title "Changes of the length of day" can apply to ΔT (and the associated LOD), to the amount of daylight in a solar day, or the length of an apparent solar day. Jc3s5h (talk) 17:55, 30 May 2012 (UTC)
 * So you would need a disambiguation page with three entries for "Changes of the length of day". How many entries would you need for ΔT? RockMagnetist (talk) 19:17, 30 May 2012 (UTC)
 * There is no need for a disambiguation page for ΔT, as far as I can tell. Anyone able to understand this article, or "ΔT", understands that in algebra, any Roman or Greek letter may be used as a variable and defined to represent any quantity, and that Δ may be pre-pended to any such variable to indicate the change in the variable. It is not the practice in Wikipedia to create disambiguation pages consisting of every published usage of every variable that has been so defined. ΔT is distinct from such variables because it is the name used for the topic by professionals in the field, and there is no corresponding full-length name. — Preceding unsigned comment added by Jc3s5h (talk • contribs) 19:23, 30 May 2012


 * Oppose merger for reasons discussed at AfD. -- 202.124.74.1 (talk) 00:14, 31 May 2012 (UTC)


 * I am going to close this discussion and delete the merger tags. I am no longer in favor of it either. RockMagnetist (talk) 04:47, 2 June 2012 (UTC)

Single-source theory
The theory section is unbalanced. It appears to be covering the theory in a single research article (Volland 1996). Several mechanisms have been proposed for LOD changes, so devoting so much space to one theory gives it undue weight. Also, a reliable third-party source should be found to demonstrate that it is not a fringe theory. RockMagnetist (talk) 15:18, 8 June 2012 (UTC)
 * The problem isn't so much one of a single theory (in the sense of rival, competing theories) as it is one of a single factor explanation, when there are several generally accepted factors that all influence the changes of the length of day. These include the steady, long term, changes due to the tidal transfer of angular momentum between the Moon and the Earth; the medium term changes caused by the changing figure of the Earth; and the rapid fluctuations due to the atmospheric coupling discussed in the article.
 * A complete article should discuss all of these factors, perhaps beginning with the steady long term changes and ending with the more rapid atmospheric coupling. --SteveMcCluskey (talk) 03:55, 12 June 2012 (UTC)
 * One factor contributing to the imbalance in this article is that it was first drafted by User:Bnland, whose edits focus on the work of Hans Volland, and whose work he frequently cites.. It appears this is a single purpose account and the editor's work, while reflecting real expertise, should be scrutinized for lack of balance. The descriptions in the images  and, which User:Bnland uploaded, suggest that he created the images published in Volland's book, in which case we may be facing a form of self promotion.
 * It may also be worth noting that another single purpose account, User:Ennasus.k, also edits in the same narrow area. SteveMcCluskey (talk) 01:25, 16 June 2012 (UTC)
 * I just looked at a few of Bnland's and Ennasus.k's images on the commons. According to the EXIF metadata, they both use the same model scanner at the same resolution settings.  Given their similar editing patterns, this is beginning to look like a case of sockpuppetry, although it is not a disruptive one. SteveMcCluskey (talk) 01:20, 17 June 2012 (UTC)

Dispute the accuracy
I dispute the accuracy of this entire article. The errors are too numerous to list, so I will start at the beginning and show the density of errors in just the first few paragraphs. And that's just the first few paragraphs. Jc3s5h (talk) 16:13, 15 June 2012 (UTC)
 * 1) "The day is normally considered a unit of measurement of the period for the rotation of the Earth. The length of this period changes, as the Earth's rotation is not constant, and for the solar day, the start and end points are not constant, as the Earth revolves around the Sun, shifting these points." Since the start and end points are not defined, this statement is meaningless.
 * 2) "The Earth's rotation relative to the Sun and its orbit about the Sun determine our standard time of one day and one year. According to Kepler's second law, the movement of the Earth one an ellipse is not constant." The second sentence is so ungrammatical that it has no meaning.
 * 3) "Therefore, a mean solar day of 86400 seconds has been introduced where one SI second is its mean value measured between 1750 and 1892 and chosen by S. Newcomb as the ephemeris second." An ephemeris day is different from a mean solar day. "Deviations from the true solar day are given by the equation of time." Deviation of what from the true solar day. Also, "true solar day" is undefined.
 * 4) "Currently, the second is slightly longer than the SI second, and leap seconds have to be used from time to time to correct for those differences." Which second is longer than the SI second?
 * 5) "Indeed, the lunar tidal torque acting on the tidal bulge of the ocean together with the effect of oceanic friction causes a secular spindown of the Earth's rotation by about 1.5 ms per century in the length of the day (LOD)." The stated cause is only one of two major causes.


 * Answer: Concerning the four first points, one may see the article "Earth`s Rotation". I have restriced myself in the reviced form to the term mean solar day which- I hope- is well defined. Concerning point 5, I do not know a second cause. Why does the user Jc3s5h not introduce himself his version? I hope is has become clear that my intention is merely to describe the  short term changes of LOD (days to a few years). Bnland 12:25, 18 November 2012 (UTC)  — Preceding unsigned comment added by Bnland (talk • contribs)


 * Bnland's comment clarifies what he had in mind in creating this article. He was not dealing with the long term astronomical changes in LOD caused by tidal acceleration or with mid-term changes caused by variations in the Earth's moment of inertia but with short term changes caused by atmospheric phenomena.  This makes my earlier comments about LOD in response to the proposal to merge this article with ΔT irrelevant.


 * It also suggests several ways to move forward on this article:
 * One way would be to restrict it explicitly to short term fluctuations in the length of day by rewriting the introduction and (perhaps) changing the title to Fluctuations in the length of day.
 * The second, which I prefer somewhat, would be to restructure the article with three sections:
 * One dealing with long term changes in the length of day,
 * One dealing with mid-term changes in the length of day,
 * One dealing with short term changes in the length of day (which would take the present article as the starting point).
 * Anyone have any comments on these options? --SteveMcCluskey (talk) 17:58, 18 November 2012 (UTC)

Answer: Thank you very much for so quick an answer. If you look into the last version of the article, you may find that I restricted myself to your first suggestion concentrating on the short time fluctuations. I believe that the long term changes have already been treated in the article Earth's rotation. I shall change the title according to your suggestion Bnland 11:48, 19 November 2012 (UTC)