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Old December 12th 17, 09:01 AM posted to sci.astro.amateur
Martin Brown[_3_]
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Posts: 189
Default The Equation of Time(keeping)

On 09/12/2017 14:53, Mikko wrote:
In article ,
"Chris.B" wrote:

Accurate clocks have been running to sidereal time for far longer than you
seem to realise.


Have you got any evidence?


Ptolemy's Almagest Volume III shows conclusively that the variable speed
of the sun across the heavens was well known to the educated ancients.
Although he explained it with circular epicycles rather than an
elliptical orbit he had computed pretty good tables for correcting solar
time. Epicycles were a crude predecessor of Fourier analysis.

https://en.wikipedia.org/wiki/Equati...on_and_E gypt

I can't find anywhere online with free access though. Closest is:

https://www.sciencedirect.com/scienc...15086013000530

Full article is behind a paywall.

The accuracy of the best clocks before pendulum clocks was abut 15
minutes per day. Before about 1650 the best pendulum clocks'
accuracy was about 10 seconds per day. In order to determine the
equation of time with a clock even one second per day, achieved by
Harrison in about 1760, is very little. Only in 1870 was accuracy of
0.1 seconds per day achieved, and equation of time determined with
a clock.


To measure the day to day variation directly you need this sort of
precision and a transit instrument to go with it. But to notice the
variation of the suns motion against the constellations at different
times of the year he could watch the movement of the sun against the
fixed stars. The suns motion was known to be uneven from the first
development of water clocks and calendars by the Babylonians.

The Chinese even had a mercury based liquid clock that was not subject
to the same viscosity problems as water. It kept better time year round.

--
Regards,
Martin Brown