[tz] Unearthly time zone in the news

Paul Eggert eggert at cs.ucla.edu
Sun Apr 7 22:27:53 UTC 2024

On 2024-04-03 22:51, Steve Allen via tz wrote:
> Ironically, as soon as that agreement went into
> effect the place over which the mean sun stands at 12:00 Universal
> Time began an increasing deviation eastward from Greenwich.

Yes, and it's also ironic that although the ITRF2020 definition of the 
prime meridian has reached new levels of accuracy (about 1 mm at the 
equator![1]), that meridian currently passes about 100 meters east of 
the Airy Transit Circle at Greenwich. Although there are good reasons[2] 
for the 100 meter discrepancy, this can all be pretty confusing to 
amateurs such as myself.

[1]: Altamimi Z, Rebischung P, Collilieux X, Métivier L, Chanard K. 
ITRF2020: an augmented reference frame refining the modeling of 
nonlinear station motions. J Geod 97, 47 (2023). 
[2]: Malys S, Seago JH, Pavlis NK, Seidelmann PK, Kaplan GH. Why the 
Greenwich meridian moved. J Geod 89, 1263–1272 (2015). 

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