[time-nuts] UTC and leap seconds

[jimlux]

Magnus Danielson wrote:
> On 06/12/2010 03:36 PM, jimlux wrote:
<bunch o' stuff>

> While it would be fun to know, the practical impact of such a change is 
> very, very small, to the level of being ignored. Considering of a major 
> event actually consisting of many hundreds of earth quakes spread over a 
> rather longish period, it becomes more interesting to see how the 
> aggregate behaves. But you also needs to understand what the effect was 
> prior to the event as it built up. What is the effect over a 1000 year 
> period (a short period in geological sense)? Consider the build-up of 
> pressure and magma under a volcano, which progresses over many years 
> before it finally accelerate. Gravimeters is routinely used to monitor 
> this build-up. There are thus more sources to consider. Someone is 
> probably studying that.
> 

That's one of the things that missions like GRACE (earth) and GRAIL 
(moon) are designed to do.  They make very high precision measurements 
of the gravity field of the body around which they orbit. It's done by 
measuring the  distance between a pair of satellites  very, very 
precisely.  The measurement uses phase measurements on RF signals 
derived from high performance ovenized quartz oscillators (USOs).  Hence 
the relevance to timenuts... good clocks are used everywhere...