[time-nuts] Re: Brain Burp re Noon and the Sun!

[Steve Allen]

On Thu 2023-11-23T22:59:53+0000 Poul-Henning Kamp via time-nuts hath writ:
> Even with +/- 15 minutes of pictures and quite advanced imageprocessing,
> it was not possible for me to nail the moment of shortest shadow better
> than approx 40 seconds.

Looking at the azimuth of the sun visually yields about the same level
of uncertainty.  Using the azimuth of a long sun shadow allows a
little better on any given day, but either way this is telling us why
astronomers shifted to measuring sidereal time to calculate mean solar
time at subsecond precision.

Worse for the sundial worshipper, from year to year the Gregorian
calendar plus lunar and planetary perturbations still mean that raw
measurement leaves a range of around 30 s in the determination of
noon.  See the zoomed-in plots of all the analammata during my
lifetime and the span of meridian crossings for all of them

https://www.ucolick.org/~sla/temporary/myanalemma.pdf

It is imperative to have worldwide agreement on the value for the
basis of civil time to a microsecond or better.  There is no point in
having the value of civil time try to track earth rotation to better
than 30 s.

--
Steve Allen                    <sla at ucolick.org>              WGS-84 (GPS)
UCO/Lick Observatory--ISB 260  Natural Sciences II, Room 165  Lat  +36.99855
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