[LEAPSECS] How good could civil timekeeping be?
dot at dotat.at
Thu Feb 14 09:07:52 EST 2008
On Wed, 13 Feb 2008, Rob Seaman wrote:
> The "day" is a key concept in our civilization. The "mean solar day" is
> the natural way to implement this. Sundials have nothing to do with the
> mean solar day, but rather the apparent solar day.
How does the mean solar day relate to ephemeris time? Between the period
where time signals were based on observing solar transitions and the
period where time signals were based on atomic clocks, official time was
ephemeris time. ET is more uniform than the Earth's rotation so a second
of ET is not 1/86400 day any more than an SI second is - and of course the
final definition of the SI second was chosen to match ET.
If we can imagine what things might have been like if essens had a
different period, can we imagine how astronomers would have handled the
discrepancy between ET and UT1 in the absence of atomic clocks?
f.a.n.finch <dot at dotat.at> http://dotat.at/
WEST VIKING: NORTHEASTERLY VEERING SOUTHERLY 3 OR 4. ROUGH. FAIR. GOOD.
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