[LEAPSECS] Mean ... Orbits

[Tony Finch]

On Fri, 4 Feb 2011, Steve Allen wrote:

>

> But cesium chronometers became available at the very same IAU meeting

> which defined UT2, and by the time cesium had been calibrated with ET

> and UT2 it was already evident that cesium revealed the earth, and

> thus UT2, was badly irregular.


I thought that this had been established before WWII, by highly stable
quartz clocks.


> So the time bureaus recognized that it was impractical to follow the

> CCIR recommendation, that broadcast signals wanted to be as regular as

> possible, and much more regular than UT2.  So for the sake of broadcasts

> the time bureaus created a cesium-regulated time scale aimed at roughly

> following UT2.


I got the impression that the key problem in the 1950s was that it
required lengthy observations to derive time and frequency corrections.
They had switched from using solar transitions to lunar occlusions because
the stability of the orbit of the moon is much greater than the rotation
of the earth. But this was not good enough for real-time broadcasts of
stable time and frequency references. Hence the rapid switch to atomic
clock references when they became available.

Tony.
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