Talk:Universal Time

Mean Second UT1

Ladies Gentlemen,

Please let me say, at my talk page, I have introduced the notion of mean second UT1. Your comments there, or here, will be well appreciated.

With regards and friendship. Georges Theodosiou. The Straw Man. Georges T. (talk) 08:20, 18 January 2017 (UTC)

UT1R & UT1S

This seems to be wrong:

UT1R [...] includes 62 smoothing terms, with periods ranging from 5.6 days to 18.6 years.

Actually, that is (was) named UT1S; UT1R includes 41 smoothing terms with periods up to 35 days only. IERS Conventions (2010), p. 123, 178, IERS Conventions (1996), p. 73.

BTW, there are also references to UT2R which is UT1R (or sometimes UT1S?) with periodic seasonal variations removed. --92.75.49.5 (talk) 21:41, 27 November 2017 (UTC)

Variety of English?

This article is inconsistent in its use of English. "Synchronise" is British English but "synchronize" is usually American English. Since UT is a successor to GMT and is associated with Greenwich, I suggest British English is more appropriate for this article. Jc3s5h (talk) 18:02, 14 March 2023 (UTC)

Actual Clock?

Is there a single clock somewhere to which all others are referenced? How is the time to be set on that clock determined? How do the other clocks reference that that one? 74.127.201.97 (talk) 12:43, 17 January 2024 (UTC)

No. National time laboratories such as the US National Institute of Standards and Technology disseminate time signals, such as WWV, controlled by a master clock for that laboratory, which is constantly checked against other clocks in the same lab. The times from the various time labs are compared to each other are computed by the International Earth Rotation and Reference Systems Service. Each month they publish a "Bulletin B" which indicates how well an individual lab agreed with the weighted average of all the participating labs. The International Bureau of Weights and Measures gathers real time information from the participating time laboratories and each month issues a "Circular T" which shows the difference between UTC, calculated after-the-fact as a weighted average, and the time at each participating lab. Jc3s5h (talk) 19:09, 17 January 2024 (UTC)

Just to add some context, these are atomic clocks, which are extraordinarily precise. So any differences between them are so small as to be irrelevant to almost everybody. For more info, see Atomic clock#Accuracy--𝕁𝕄𝔽 (talk) 20:06, 17 January 2024 (UTC)

The questioner may not appreciate that the Earth is a terrible clock by comparison with atomic clocks or even with a fairly average digital watch; it gains (or loses!) a second over a ten year period – ish. Consequently we have to add (or subtract) leap seconds occasionally so that solar noon at the IERS Reference Meridian happens at 12:00 on the dial.--𝕁𝕄𝔽 (talk) 16:36, 18 January 2024 (UTC)

In my experience good quality watches may gain or lose a second over a month. Since 1972 there have been 27 leap seconds, so about 1 every other year, on average. If the technology in a modern digital watch is refined into a laboratory crystal-controlled clock (not atomic) clock it can detect the variations in the earth's rotation, but won't be good enough to use for years at a time, so in the 1930s and 1940s these clocks had to be corrected to astronomical observations. Only with the invention of the atomic clock in the 1950s did it become an option to dispense with astronomical observations. Jc3s5h (talk) 17:40, 18 January 2024 (UTC)

I'm sure you are right. I confess that I haven't worn a wristwatch in at least ten years. But STANDS TO REASON! 𝕁𝕄𝔽 (talk) 20:02, 18 January 2024 (UTC)

February 2024 citation needed templates

A number of citation needed templates were added in late February 2024 and I have been trying to find suitable citations. One passage claimed that methods such as GPS satellite orbits and lunar laser ranging were used to determine UT1. I looked at the website of one of the key scientific bodies involved with UT1, the [[International Earth Rotation and Reference Systems Service. They have a subpage with their conventions. The glossary of the IERS Conventions (2010) has this definition:

UT1 angle of the Earth's rotation about the CIP axis defined by its conventional linear relation to the Earth Rotation Angle (ERA). It is related to Greenwich apparent sidereal time through the ERA (see equation of the origins). It is determined by observations (currently from VLBI observations of the diurnal motions of distant radio sources). UT1 can be regarded as a time determined by the rotation of the Earth. It can be obtained from the uniform time scale UTC by using the quantity UT1−UTC, which is provided by the IERS. [NFA Glossary], p. 123.

Since this definition makes no mention of anything but VLBI, I removed the claims about the other methods from the article. Jc3s5h (talk) 17:01, 1 March 2024 (UTC)