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
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