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Old October 26th 17, 02:12 PM posted to sci.astro.amateur
Gerald Kelleher
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Default Time and timekeeping

On Thursday, October 26, 2017 at 9:13:32 AM UTC+1, Martin Brown wrote:
On 25/10/2017 18:59, Gerald Kelleher wrote:
The theorists assume they are discussing time when it is really
timekeeping they are referring to. Of course this goes back to a
person who decided to define timekeeping as time itself using a
calendar based facility known as the Equation of Time -


The equation of time is just the first order correction for a whole host
of other effects that alter the spin of the Earth. The transit of the
sun makes for a very poor time standard by comparison with a star.


This is a foolish statement, the 'Equation of Time' is a timekeeping facility that only works within the calendar framework so before the theorists so running after a notion that 'clocks measure' time, the job of a clock is merely to maintain a constant pace in terms of the AM/PM cycle or its subdivisions of hours,minutes and seconds. The language of astronomy and timekeeping is to determine where the dynamics of the Earth's orbital motion (producing the natural inequality in the total length for each meridian crossing of the Sun) meshes with human devised clock noon. The primary understanding is that the natural day with its variability is the anchor for the 24 hour weekday and the division into constant hours ,minutes and seconds.

The creation of the Lat/Long system imposed on the Earth's daily rotational geometry in terms of time/distance separation (15 degrees/hour) exploits the equalizing effects of the Equation of Time so that the 'average' 24 hour day is translated into 'constant' rotation at 15 degrees per hour, 1 degree for every 4 minutes or any other correlation. It is that neat trick of converting 'average' to 'constant' that allowed for terrestrial Lat/Long coordinates and more importantly the close but not exact correspondence between the 24 hour weekday and one rotation.

The RA/Dec framework is basically a shortcut which is built on the previous principle supplied by the Equation of Time. The EoT required a meridian line which followed the particular meridian from pole to pole where the observation is made. Only when this line was constructed could the observer determine natural noon on that meridian -

" Draw a Meridian line upon a floor... and then hang two plummets, each by a small thred or wire, directly over the said Meridian, at the distance of some 2. feet or more one from the other, as the smalness of the thred will admit. When the middle of the Sun (the Eye being placed so, as to bring both the threds into one line) appears to be in the same line exactly... you are then immediately to set the Watch, not precisely to the hour of 12. but by so much less, as is the Aequation of the day by the Table." Huygen's

https://adcs.home.xs4all.nl/Huygens/06/kort-E.html

The Ra/Dec observations are homocentric ,meaning that any two forefront references do not follow the Earth's rotation from pole to pole but track around the observer. The crucial point here is that unless an observer actually goes further back in history to the creation of the 4 year/ 4 orbital period calendar cycle can they make some progress and discover why it is important not to mix up the reference systems for either the Earth's daily/orbital motions or timekeeping. This language is as definite and intricate as computer language or any engineering language but few are familiar with the components.

Your description is purpose designed for calendar based RA/Dec predictions but at the expense of an astronomy that is bursting at the seams with new imaging. I have learned your language but unfortunately you may have to go back further in history to look at the few other astronomical/timekeeping languages to sort the whole thing out in an honest way.