This article is written in American English, which has its own spelling conventions (color, defense, traveled) and some terms that are used in it may be different or absent from other varieties of English. According to the relevant style guide, this should not be changed without broad consensus. |
This article is rated C-class on Wikipedia's
content assessment scale. It is of interest to the following WikiProjects: | |||||||||||||||||||||||||||||||||||||||||
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This article was nominated for merging with Changes of the length of day on 30 May 2012. The result of the discussion was do not merge. |
To basically sum up what Delta T is you just use the equation TT−UT1=Delta T.
—
68.47.224.141 on July 1, 2004.
Delta T is given by 32.184 + (TAI−UTC) + (UT1−UTC) seconds, where (TAI−UTC) is the number of leap seconds. (UT1−UTC) changes continually as the Earth's rotational rate varies; it's actual value must be determined by observation, but is often predicted by formulas. Leap seconds are adjusted to keep abs(UT1−UTC) below 1.0 seconds.
— Preceding unsigned comment added by 184.58.1.86 ( talk) 18:28, 29 May 2020 (UTC)
The title of this article was changed by Michael Hardy on December 30, 2004 to Delta minus T and all other instances of it, both here and in other articles, to Δ − T because he misread the hyphen in delta-T as a minus sign. Accordingly, I have changed its title to Delta T, which seems to be more popular than delta-T, to avoid further misunderstandings, and changed all other instances of it into its formal form, ΔT, as part of my rewrite. — Joe Kress 05:04, Jan 16, 2005 (UTC)
I think this sentance needs clarification. What is "−500 Earth's faster rotation"?
Just to advise, I work in Air Conditioning and Delta T is commonly used in Psychrometrics (the study of air) to indicate the temperature difference.
A typical formula is , where: Mass (flow rate) multiplied Constant specific heat capacity (of air) multiplied by the ΔT (difference in temperature) will result in Q (Heat added to air). (Note: This isn't 100% accurate, I'm attempting to find specific information on this which can be used) - ~Xytram~ 15:38, 22 November 2006 (UTC)
It appears we have problems with a symbol used for the tidal acceleration of the Moon's mean motion. There used to be a capital Gamma here. However the literature uses a dotted n. Recently I approximated this with an accented n (ń) from the Wiki markup characters, which I found acceptable because primed variables are commonly used to indicate derivatives. Joe Kress inserted a proper unicode char. Unfortunately it does not disply in my Internet Explorer, and I suppose this will bother more readers. Therefore I suggest to write d(n)/dt , for which the dotted n is an abbreviation; I believe it was originally in this article anyway. Tom Peters 09:46, 3 January 2007 (UTC)
The article currently says that TT is based on TAI and inherits its non-uniformity at the 10-14 level. This is not correct: TAI is actually a realisation of TT, and TT is by definition perfectly uniform. I corrected the article diff, but User:Joe Kress reverted my correction. What's your reasoning, Joe Kress? Your edit summary didn't explain what was wrong with my text. 195.224.75.71 14:28, 7 February 2007 (UTC)
I'm reapplying the change. The relation between TT and TAI is already explained in their articles, and Terrestrial Time has included a " platonic" link since I revised it in 2006-04. You must have seen that link, although you don't remember it, because you edited that article yourself for style shortly after my work. Unadorned "TT" does, strictly, refer only to the theoretical time scale. "TT = TAI + 32.184 s" is a common misunderstanding, and to propagate it (and all that it implies) is wrong. I think an encyclopaedia article does need to be strictly accurate, particularly on a matter so closely related to the article's main topic. As for signing in, I prefer not to register. I'm not entirely anonymous: see my user page. Finally, the unwanted line wrapping is a misfeature of Lynx, which I put up with because it doesn't affect how the article renders. 195.224.75.71 09:59, 13 February 2007 (UTC)
I'm reasonably happy with "theoretical" in place of "platonic", which is what you've done. I disagree with your notion that Plato has to be consulted on what qualifies as platonic, but I don't want to argue over the choice of word when I think both options are OK. As you've left the rest of my material about TT and TAI intact, I'm satisfied that the paragraph is now correct. 81.168.80.170 20:13, 14 February 2007 (UTC) (Zefram from a different IP address)
This could pose a problem in the distant future; I don't think fortnights of daylight and darkness would be well tolerated by terrestrial life. Has any thought been given to a plan to grind up the moon or otherwise diminish the threat it poses (admittedly very long term) to public safety? knoodelhed 04:04, 9 February 2007 (UTC)
The first paragraph of the article states: "[the extensive ice age icecaps melted], allowing the land under them to begin to rebound upward in the polar regions, which has been continuing and will continue until isostatic equilibrium is reached." Fair enough: I've hear this theory before, and have no problem with it. However, the article then goes on to say: "This "glacial rebound" brings mass closer to the rotation axis of the Earth, which makes the Earth spin faster (law of conservation of angular momentum)..." (my emphasis),
That doesn't make any sense. Surely the ground is moving upwards as stated earlier in the paragraph, due to rebounding after the ice age glaciers melted. Just because this rebounding is "in the polar regions", that doesn't make the direction of rebounding towards the centre of gravity; if it was, the land would be going down, not up. No, the net movement is outwards, away from the centre of gravity and not towards it.
Someone please explain if I have missed something here, or if this is the problem I think it is.
WikiReaderer 01:14, 23 October 2007 (UTC)
"Terrestrial Time (TT) is a theoretical uniform time scale, defined to provide continuity with the former Ephemeris Time (ET)." This sounds unnecessarily close to "theoretically uniform". If it means what I think it means, Terrestrial Time is an invariant time scale, and there's nothing "theoretical" about it, except that it's artificial, in the sense that it's defined independently of astronomical observations. "Continuity with" is meaningless to me. Perhaps that's supposed to indicate that TT is close to ET. Beats me. How can there be continuity between the two concepts? "Former Ephemeris Time" seems to me to imply that there are at least two definitions of Ephemeris Time, one "former" and another other than "former", which is misleading. If that means what I think it means, "former" ought to be deleted entirely, or replaced by something like "formerly used (for something)". Unfree ( talk) 01:16, 7 November 2009 (UTC)
In the very long term, it is indeed true to state (in the main article): "[Delta-T] will continue to increase at an ever faster (quadratic) rate in the future".
At the same time, it is interesting to note the diagram on p.33 in the [UK publication] New Scientist of 30th January 1999, illustrating Stephenson and Morrison's suggestion that there might be an oscillation effect - so, (if that oscillation is real), during the next few centuries Delta-T will not increase quite as much as envisaged. But perhaps this is still too speculative to qualify for a mention on the main page, is it? DLMcN ( talk) 20:50, 18 March 2011 (UTC) DLMcN ( talk) 20:52, 18 March 2011 (UTC)
The Bibliography near the bottom of our main page does actually include Stephenson and Morrison's paper "Long-term fluctuations in the Earth's rotation: 700 BC to AD 1990", and the [additional] abstract given by JSTOR ends with the remark: "Moreover, it is shown that besides this accelerative component, there is a fluctuation in the l.o.d. with a semi-amplitude of ~4 ms and a period of ~1500 yr". DLMcN ( talk) 21:13, 18 March 2011 (UTC)
From Unknown, initially rating this article as C-Class on the project's quality scale and Low-importance on the project's importance scale. Senator2029║ talk 06:47, 10 December 2011 (UTC)
2A01:E34:EC0A:CB40:CED:BCDA:7E58:C7C5 ( talk) 05:39, 7 September 2022 (UTC) Earth rotation fictitious time gap (ERFTG) would be a suitable and pertinent name.
The article sorely needs to be renamed: "ΔT" is not a name but merely a symbol that is meaningful only to specialists of this particular discipline -- i.e., an "algebraic jargon". Wikipedia articles must be written -- and named -- for the benefit of non-specialist readers. Thus, for example, the article about temperature must be titled "temperature" and not "T".
So please find (or invent) an appropriate name for this quantity, using English words, and rename the article with it. --
Jorge Stolfi (
talk) 03:24, 24 May 2012 (UTC)
"ΔT" has a much more specific meaning than "Time differential" or "Solar/Astronomical time differential". It is the difference between, in effect, atomic time at sea level on the surface of the earth and UT1, which is a specific approximation to mean solar time. Jc3s5h ( talk) 12:03, 25 May 2012 (UTC)
This article should simply be named "Difference between Universal Time and Terrestial Time". (In accordance with the policy that article names should not be abbreviations). T R 13:31, 7 June 2012 (UTC)
Let's look at a reliable source, the glossary of the Astronomical Almanac. There is an entry for ΔT and it is defined as "the difference between Terrestrial Time (TT) and Universal Time (UT): ΔT=TT-UT1". There are no entries beginning with the word "difference". There is no entry named "Time differential". There are no entries named "Solar/Astronomical time differential" and no similar terms that begin with "solar" or "astronomical".
McCarthy and Seidelmann (p. 124, see article for full bibliographic information) use "ΔT and Ephemeris Time Revised" as a section title.
So I believe we should follow the reliable sources and keep the article where it is. It would be appropriate to add a redirect from "Difference between Terrestrial Time (TT) and Universal Time (UT1)". Of course I would change my mind if someone can find a reliable source that uses some multi-word term for ΔT as a title, glossary entry, or dictionary entry. Jc3s5h ( talk) 14:00, 7 June 2012 (UTC)
The name of this article is clearly inappropriate and should be changed to something more descriptive. "T" is used for too many things in different contexts. TimothyRiass suggestion "Difference between Universal Time and Terrestial Time" sounds fine for me. Using sources that deal specifically with astronomy and time to support the current name is totally irrelevant for the name of an article in a general encyclopaedia. Liiiii ( talk) 15:58, 27 August 2015 (UTC)
Leap Second links here as an expansion of a section "Slowing rotation of the Earth". And there is another article Day length fluctuations. So this article should be titled something like Day length increase. Explain the phenomenon then introduce Delta T as effectively a measure of the cumulative increase since about 1900 (although formally it's the measure of theach increase since 1970 plus an offset). Humphrey Jungle ( talk) 23:19, 18 October 2018 (UTC)
I recently rated this article for Wikiproject Physics and was asked to give some pointers on how it could be made up to a B Class ( criteria here). Looking through the assessment criteria:
I'll address each point in order;
Lastly it's worth noting that the article should generally be compliant with the Manual of Style.
I hope this helps! I'd be happy to reassess if any editors feel these points have been addressed. — Preceding
unsigned comment added by
Newty23125 (
talk •
contribs) 14:49, 10 June 2012 (UTC)
Hello fellow Wikipedians,
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I updated the values of Delta T based on the latest work of Morrison and Stephenson, and added a reference to support the update. Acorann left my updates but deleted the reference, saying that there were already references to the work of L. V. Morrison and F. R. Stephenson. The existing references do not include all of the material I consulted. I could add the additional references, but combining works together, even from the same authors, is Original Research. To avoid that, I did the combining in a paper, which I referenced. Should I just add the additional references, or should I reference the paper that combines their results? John Sauter ( talk) 21:36, 19 May 2016 (UTC)
The recent addition of section headings sharpened a tension in this article between the idealistic version of a simple quadratic expression for ΔT, now in a separate section of Values prior to 1955, and the non-quadratic form of non-tidal terms discussed in the rest of the article. It leaves the reader with the impression that the complexities discussed earlier in the article can be ignored prior to 1955, when in fact, they really become significant when considering such long-term calculations.
I'm not certain how best to go about resolving this but it seems to me that the simple quadratic expression should be presented as a simplified model, while the more complex analyses based on the historical observations collected by Stephenson and Morrison more adequately should be presented as more complete expressions of the Earth's changing rotation over the long term. -- SteveMcCluskey ( talk) 20:52, 6 December 2016 (UTC)
This article of last December is probably the most comprehensive and up-to-date on this subject, so I suggest it be cited. Zero talk 11:14, 31 October 2017 (UTC)
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The given equations do not calculate delta T. They also introduce a symbol T meaning the Earth's rotation period, but in the expressionext delta T the symbol T means the time since the epoch. Humphrey Jungle ( talk) 23:24, 18 October 2018 (UTC)
I've replaced T in the equations with P. Humphrey Jungle ( talk) 08:57, 7 November 2018 (UTC)
The UK Hydrographic Office in Taunton, Somerset, has issued a diagram which gives a really excellent illustration of the final statement in the opening paragraph of this Wikipedia article - [namely: "Since 2017, the length of the day has happened to be very close to the conventional value, and ΔT has remained within a second of 69 seconds"].
This diagram is temporarily viewable in my private website at http://www.dlmcn.com/deltaT_March_2023_Short.pdf ... It could presumably be uploaded here if we get permission from the UK Hydrographic Office? -- DLMcN ( talk) 20:13, 6 March 2023 (UTC)
That^ UK office is presently servicing its website - so the diagram will probably be published officially quite soon. -- DLMcN ( talk) 21:28, 6 March 2023 (UTC)
Ref: CS-271713-G8T5 Your enquiry has been ... logged under this unique Reference Number, which should be quoted in any further correspondence with us.
Good day,
Thank you for your enquiry, this has been shared with our HMNAO team and they have provided the following;
“Thank you for your kind words, we are happy for you to use our diagrams for the Delta-T Wikipedia article. Unfortunately due to our site’s essential maintenance we do not have a permanent link to these images. To complicate matters further we also update these diagrams automatically every month and so placing them in another location in a static fashion would quickly become obsolete.
For now we are happy to send you the new files each month for updating, and when our website returns we will be sure to let you know of their new location.”
Kind regards Shaun Cockram <customerservices@ukho.gov.uk>, Customer Services, UK Hydrographic Office, Admiralty Way, TAUNTON, Somerset, UK, TA1 2DN, Tel: +44 (0)1823 484444 www.Admiralty.co.uk
-- DLMcN ( talk) 19:28, 14 March 2023 (UTC)
This article is written in American English, which has its own spelling conventions (color, defense, traveled) and some terms that are used in it may be different or absent from other varieties of English. According to the relevant style guide, this should not be changed without broad consensus. |
This article is rated C-class on Wikipedia's
content assessment scale. It is of interest to the following WikiProjects: | |||||||||||||||||||||||||||||||||||||||||
|
This article was nominated for merging with Changes of the length of day on 30 May 2012. The result of the discussion was do not merge. |
To basically sum up what Delta T is you just use the equation TT−UT1=Delta T.
—
68.47.224.141 on July 1, 2004.
Delta T is given by 32.184 + (TAI−UTC) + (UT1−UTC) seconds, where (TAI−UTC) is the number of leap seconds. (UT1−UTC) changes continually as the Earth's rotational rate varies; it's actual value must be determined by observation, but is often predicted by formulas. Leap seconds are adjusted to keep abs(UT1−UTC) below 1.0 seconds.
— Preceding unsigned comment added by 184.58.1.86 ( talk) 18:28, 29 May 2020 (UTC)
The title of this article was changed by Michael Hardy on December 30, 2004 to Delta minus T and all other instances of it, both here and in other articles, to Δ − T because he misread the hyphen in delta-T as a minus sign. Accordingly, I have changed its title to Delta T, which seems to be more popular than delta-T, to avoid further misunderstandings, and changed all other instances of it into its formal form, ΔT, as part of my rewrite. — Joe Kress 05:04, Jan 16, 2005 (UTC)
I think this sentance needs clarification. What is "−500 Earth's faster rotation"?
Just to advise, I work in Air Conditioning and Delta T is commonly used in Psychrometrics (the study of air) to indicate the temperature difference.
A typical formula is , where: Mass (flow rate) multiplied Constant specific heat capacity (of air) multiplied by the ΔT (difference in temperature) will result in Q (Heat added to air). (Note: This isn't 100% accurate, I'm attempting to find specific information on this which can be used) - ~Xytram~ 15:38, 22 November 2006 (UTC)
It appears we have problems with a symbol used for the tidal acceleration of the Moon's mean motion. There used to be a capital Gamma here. However the literature uses a dotted n. Recently I approximated this with an accented n (ń) from the Wiki markup characters, which I found acceptable because primed variables are commonly used to indicate derivatives. Joe Kress inserted a proper unicode char. Unfortunately it does not disply in my Internet Explorer, and I suppose this will bother more readers. Therefore I suggest to write d(n)/dt , for which the dotted n is an abbreviation; I believe it was originally in this article anyway. Tom Peters 09:46, 3 January 2007 (UTC)
The article currently says that TT is based on TAI and inherits its non-uniformity at the 10-14 level. This is not correct: TAI is actually a realisation of TT, and TT is by definition perfectly uniform. I corrected the article diff, but User:Joe Kress reverted my correction. What's your reasoning, Joe Kress? Your edit summary didn't explain what was wrong with my text. 195.224.75.71 14:28, 7 February 2007 (UTC)
I'm reapplying the change. The relation between TT and TAI is already explained in their articles, and Terrestrial Time has included a " platonic" link since I revised it in 2006-04. You must have seen that link, although you don't remember it, because you edited that article yourself for style shortly after my work. Unadorned "TT" does, strictly, refer only to the theoretical time scale. "TT = TAI + 32.184 s" is a common misunderstanding, and to propagate it (and all that it implies) is wrong. I think an encyclopaedia article does need to be strictly accurate, particularly on a matter so closely related to the article's main topic. As for signing in, I prefer not to register. I'm not entirely anonymous: see my user page. Finally, the unwanted line wrapping is a misfeature of Lynx, which I put up with because it doesn't affect how the article renders. 195.224.75.71 09:59, 13 February 2007 (UTC)
I'm reasonably happy with "theoretical" in place of "platonic", which is what you've done. I disagree with your notion that Plato has to be consulted on what qualifies as platonic, but I don't want to argue over the choice of word when I think both options are OK. As you've left the rest of my material about TT and TAI intact, I'm satisfied that the paragraph is now correct. 81.168.80.170 20:13, 14 February 2007 (UTC) (Zefram from a different IP address)
This could pose a problem in the distant future; I don't think fortnights of daylight and darkness would be well tolerated by terrestrial life. Has any thought been given to a plan to grind up the moon or otherwise diminish the threat it poses (admittedly very long term) to public safety? knoodelhed 04:04, 9 February 2007 (UTC)
The first paragraph of the article states: "[the extensive ice age icecaps melted], allowing the land under them to begin to rebound upward in the polar regions, which has been continuing and will continue until isostatic equilibrium is reached." Fair enough: I've hear this theory before, and have no problem with it. However, the article then goes on to say: "This "glacial rebound" brings mass closer to the rotation axis of the Earth, which makes the Earth spin faster (law of conservation of angular momentum)..." (my emphasis),
That doesn't make any sense. Surely the ground is moving upwards as stated earlier in the paragraph, due to rebounding after the ice age glaciers melted. Just because this rebounding is "in the polar regions", that doesn't make the direction of rebounding towards the centre of gravity; if it was, the land would be going down, not up. No, the net movement is outwards, away from the centre of gravity and not towards it.
Someone please explain if I have missed something here, or if this is the problem I think it is.
WikiReaderer 01:14, 23 October 2007 (UTC)
"Terrestrial Time (TT) is a theoretical uniform time scale, defined to provide continuity with the former Ephemeris Time (ET)." This sounds unnecessarily close to "theoretically uniform". If it means what I think it means, Terrestrial Time is an invariant time scale, and there's nothing "theoretical" about it, except that it's artificial, in the sense that it's defined independently of astronomical observations. "Continuity with" is meaningless to me. Perhaps that's supposed to indicate that TT is close to ET. Beats me. How can there be continuity between the two concepts? "Former Ephemeris Time" seems to me to imply that there are at least two definitions of Ephemeris Time, one "former" and another other than "former", which is misleading. If that means what I think it means, "former" ought to be deleted entirely, or replaced by something like "formerly used (for something)". Unfree ( talk) 01:16, 7 November 2009 (UTC)
In the very long term, it is indeed true to state (in the main article): "[Delta-T] will continue to increase at an ever faster (quadratic) rate in the future".
At the same time, it is interesting to note the diagram on p.33 in the [UK publication] New Scientist of 30th January 1999, illustrating Stephenson and Morrison's suggestion that there might be an oscillation effect - so, (if that oscillation is real), during the next few centuries Delta-T will not increase quite as much as envisaged. But perhaps this is still too speculative to qualify for a mention on the main page, is it? DLMcN ( talk) 20:50, 18 March 2011 (UTC) DLMcN ( talk) 20:52, 18 March 2011 (UTC)
The Bibliography near the bottom of our main page does actually include Stephenson and Morrison's paper "Long-term fluctuations in the Earth's rotation: 700 BC to AD 1990", and the [additional] abstract given by JSTOR ends with the remark: "Moreover, it is shown that besides this accelerative component, there is a fluctuation in the l.o.d. with a semi-amplitude of ~4 ms and a period of ~1500 yr". DLMcN ( talk) 21:13, 18 March 2011 (UTC)
From Unknown, initially rating this article as C-Class on the project's quality scale and Low-importance on the project's importance scale. Senator2029║ talk 06:47, 10 December 2011 (UTC)
2A01:E34:EC0A:CB40:CED:BCDA:7E58:C7C5 ( talk) 05:39, 7 September 2022 (UTC) Earth rotation fictitious time gap (ERFTG) would be a suitable and pertinent name.
The article sorely needs to be renamed: "ΔT" is not a name but merely a symbol that is meaningful only to specialists of this particular discipline -- i.e., an "algebraic jargon". Wikipedia articles must be written -- and named -- for the benefit of non-specialist readers. Thus, for example, the article about temperature must be titled "temperature" and not "T".
So please find (or invent) an appropriate name for this quantity, using English words, and rename the article with it. --
Jorge Stolfi (
talk) 03:24, 24 May 2012 (UTC)
"ΔT" has a much more specific meaning than "Time differential" or "Solar/Astronomical time differential". It is the difference between, in effect, atomic time at sea level on the surface of the earth and UT1, which is a specific approximation to mean solar time. Jc3s5h ( talk) 12:03, 25 May 2012 (UTC)
This article should simply be named "Difference between Universal Time and Terrestial Time". (In accordance with the policy that article names should not be abbreviations). T R 13:31, 7 June 2012 (UTC)
Let's look at a reliable source, the glossary of the Astronomical Almanac. There is an entry for ΔT and it is defined as "the difference between Terrestrial Time (TT) and Universal Time (UT): ΔT=TT-UT1". There are no entries beginning with the word "difference". There is no entry named "Time differential". There are no entries named "Solar/Astronomical time differential" and no similar terms that begin with "solar" or "astronomical".
McCarthy and Seidelmann (p. 124, see article for full bibliographic information) use "ΔT and Ephemeris Time Revised" as a section title.
So I believe we should follow the reliable sources and keep the article where it is. It would be appropriate to add a redirect from "Difference between Terrestrial Time (TT) and Universal Time (UT1)". Of course I would change my mind if someone can find a reliable source that uses some multi-word term for ΔT as a title, glossary entry, or dictionary entry. Jc3s5h ( talk) 14:00, 7 June 2012 (UTC)
The name of this article is clearly inappropriate and should be changed to something more descriptive. "T" is used for too many things in different contexts. TimothyRiass suggestion "Difference between Universal Time and Terrestial Time" sounds fine for me. Using sources that deal specifically with astronomy and time to support the current name is totally irrelevant for the name of an article in a general encyclopaedia. Liiiii ( talk) 15:58, 27 August 2015 (UTC)
Leap Second links here as an expansion of a section "Slowing rotation of the Earth". And there is another article Day length fluctuations. So this article should be titled something like Day length increase. Explain the phenomenon then introduce Delta T as effectively a measure of the cumulative increase since about 1900 (although formally it's the measure of theach increase since 1970 plus an offset). Humphrey Jungle ( talk) 23:19, 18 October 2018 (UTC)
I recently rated this article for Wikiproject Physics and was asked to give some pointers on how it could be made up to a B Class ( criteria here). Looking through the assessment criteria:
I'll address each point in order;
Lastly it's worth noting that the article should generally be compliant with the Manual of Style.
I hope this helps! I'd be happy to reassess if any editors feel these points have been addressed. — Preceding
unsigned comment added by
Newty23125 (
talk •
contribs) 14:49, 10 June 2012 (UTC)
Hello fellow Wikipedians,
I have just added archive links to one external link on
ΔT. Please take a moment to review
my edit. If necessary, add {{
cbignore}}
after the link to keep me from modifying it. Alternatively, you can add {{
nobots|deny=InternetArchiveBot}}
to keep me off the page altogether. I made the following changes:
When you have finished reviewing my changes, please set the checked parameter below to true to let others know.
An editor has reviewed this edit and fixed any errors that were found.
Cheers.— cyberbot II Talk to my owner:Online 08:56, 27 February 2016 (UTC)
I updated the values of Delta T based on the latest work of Morrison and Stephenson, and added a reference to support the update. Acorann left my updates but deleted the reference, saying that there were already references to the work of L. V. Morrison and F. R. Stephenson. The existing references do not include all of the material I consulted. I could add the additional references, but combining works together, even from the same authors, is Original Research. To avoid that, I did the combining in a paper, which I referenced. Should I just add the additional references, or should I reference the paper that combines their results? John Sauter ( talk) 21:36, 19 May 2016 (UTC)
The recent addition of section headings sharpened a tension in this article between the idealistic version of a simple quadratic expression for ΔT, now in a separate section of Values prior to 1955, and the non-quadratic form of non-tidal terms discussed in the rest of the article. It leaves the reader with the impression that the complexities discussed earlier in the article can be ignored prior to 1955, when in fact, they really become significant when considering such long-term calculations.
I'm not certain how best to go about resolving this but it seems to me that the simple quadratic expression should be presented as a simplified model, while the more complex analyses based on the historical observations collected by Stephenson and Morrison more adequately should be presented as more complete expressions of the Earth's changing rotation over the long term. -- SteveMcCluskey ( talk) 20:52, 6 December 2016 (UTC)
This article of last December is probably the most comprehensive and up-to-date on this subject, so I suggest it be cited. Zero talk 11:14, 31 October 2017 (UTC)
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I have just modified one external link on ΔT. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:
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The given equations do not calculate delta T. They also introduce a symbol T meaning the Earth's rotation period, but in the expressionext delta T the symbol T means the time since the epoch. Humphrey Jungle ( talk) 23:24, 18 October 2018 (UTC)
I've replaced T in the equations with P. Humphrey Jungle ( talk) 08:57, 7 November 2018 (UTC)
The UK Hydrographic Office in Taunton, Somerset, has issued a diagram which gives a really excellent illustration of the final statement in the opening paragraph of this Wikipedia article - [namely: "Since 2017, the length of the day has happened to be very close to the conventional value, and ΔT has remained within a second of 69 seconds"].
This diagram is temporarily viewable in my private website at http://www.dlmcn.com/deltaT_March_2023_Short.pdf ... It could presumably be uploaded here if we get permission from the UK Hydrographic Office? -- DLMcN ( talk) 20:13, 6 March 2023 (UTC)
That^ UK office is presently servicing its website - so the diagram will probably be published officially quite soon. -- DLMcN ( talk) 21:28, 6 March 2023 (UTC)
Ref: CS-271713-G8T5 Your enquiry has been ... logged under this unique Reference Number, which should be quoted in any further correspondence with us.
Good day,
Thank you for your enquiry, this has been shared with our HMNAO team and they have provided the following;
“Thank you for your kind words, we are happy for you to use our diagrams for the Delta-T Wikipedia article. Unfortunately due to our site’s essential maintenance we do not have a permanent link to these images. To complicate matters further we also update these diagrams automatically every month and so placing them in another location in a static fashion would quickly become obsolete.
For now we are happy to send you the new files each month for updating, and when our website returns we will be sure to let you know of their new location.”
Kind regards Shaun Cockram <customerservices@ukho.gov.uk>, Customer Services, UK Hydrographic Office, Admiralty Way, TAUNTON, Somerset, UK, TA1 2DN, Tel: +44 (0)1823 484444 www.Admiralty.co.uk
-- DLMcN ( talk) 19:28, 14 March 2023 (UTC)