[LEAPSECS] Reliability

[Rob Seaman]

Zefram wrote:


> Rob Seaman wrote:

>> It's the usual familiar layered architecture and the apparent  

>> position

>> of the Sun is from a higher layer then the - so-called - mean

>> position.

>

> Sidereal time isn't entirely linear in time either, as we all know.

> So if the mean behaviour is the more fundamental, presumably you  

> regard

> UT2R as more fundamental than UT1.


According to the IAU, sidereal time itself doesn't really exist :-)

And yet the Earth spins beneath a starry sky.


> The mean may well make a better coordinate system, but without those

> bizarre curlicues the mean wouldn't exist.



Mean solar time is highly regular and elegantly simple.  Regression to  
the mean (which I think is the notion underlying this disputation of  
terms) from unrelated measurements would not recover such a simple  
result.  Rather (to first order) the Earth spins at a constant angular  
rate.  The apparent positions of the Sun from day-to-day are not  
unrelated, they are related precisely by the fundamental angular  
velocity vector of the spinning Earth (http://www.analemma.com).

The fact that this results in apparent positions that vary  
flamboyantly reveals a number of hidden variables.  The eccentricity  
of the Earth's orbit.  The tilt of its axis.  The (near) spherical  
coordinate system on the surface of the Earth (http://en.wikipedia.org/wiki/Eratosthenes 
).

For civil timekeeping, these are irrelevant.  Civil timekeeping (even  
under the ITU proposal) is about the underlying diurnal period.  The  
curlicues obscure underlying reality, they don't create it.

Removing leap seconds (without providing an alternate mode of  
approximation) would just make the curlicues more bizarre.

Rob