On 2021-05-22 21:38, Steve Allen via tz wrote:
On Sun 2021-05-23T10:54:16+0800 Philip Paeps via tz hath writ:
This is a good point. Particularly since LMT is only "correct" for very narrow regions within any given timezone.
In general LMT is not even correct for the city at the given location.
Prior to 1834 the Nautical Almanac tabulated Greenwich Apparent Time, not Greenwich Mean Time.
As illustrated by Greenwich relative to London it was often the local university, naval academy, other closest observatory, or transit telescope owner who defined the latitude and offset of local solar time, and as stated, whether apparent or mean time was calculated, distributed, and used locally.
In the US insurers during the 19th century wrote policies which specified the expiration at noon on a particular date because it was reasonably likely that witnesses could testify as to whether the fire started while the sun was on the east side of buildings or the west side of buildings. For the purposes of the insurance legal time was local apparent solar time, not local mean solar time.
From the legal viewpoint in the English common law based legal world, which is most of the Commonwealth of Nations and former colonies including the USA, mean solar time represented by UT and some offset(s) still applies, due to pre-atomic precedents, regardless of IAU, ISO, or ITU opinions about ephemerides, atomic physics, or radio signals. If tested, I would expect the current definition of the second may have no legal basis in those jurisdictions, and it would be interesting to see if a case could be made on the technicality that times commonly used and often relied upon may not be legally valid. -- Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada This email may be disturbing to some readers as it contains too much technical detail. Reader discretion is advised. [Data in binary units and prefixes, physical quantities in SI.]