[LEAPSECS] drawing the lines

[Tony Finch]

Zefram <zefram at fysh.org> wrote:


> Actually it's got me thinking that the UT1<->ET interface wasn't so

> bad after all; maybe UT1 really *was* a time scale, and the mistake

> was just to describe it in angle units.  That is, in units that we've

> retrospectively decided were `really' angular all along.  See how tough

> the ontological bifurcation makes things?


The way I like to think about it is a bit Platonic: there are various
theoretical timescales which are the perfectly uniform proper time of some
body, e.g. what TT aims for; then there are the somewhat muddy
realisations of timescales which approach the ideal more or less closely
depending on the effort we make, e.g. TAI, or some lab's atomic time, or
what my clock says; big spinning rocks in space make fairly adequate
clocks and some of them have a lot of historical importance, and for
several reasons we put a lot of effort into measuring their motion very
precisely, e.g. UT1; but the more you concentrate on measuring precise
position, the less your activity is about getting a uniform measurement of
time.

UTC is not a timescale or an angular measurement, but an inconvenient way
of labelling the seconds of an atomic timescale to get a bad approximation
of an angle.

Tony.
-- 
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