[time-nuts] New tide gauge uses GPS signals to measure sea level change

Jim Lux jimlux at earthlink.net
Fri May 30 19:05:17 UTC 2014

On 5/30/14, 2:41 AM, Dr. David Kirkby wrote:
> On 28 May 2014 14:06, "Tom Holmes" <tholmes at woh.rr.com> wrote:
>> Which begs the question: just where the heck, exactly, is the center of
> the
>> Earth given that it is in the 'middle' of a molten and dynamic core.
> I always thought that the centre was molten. There was something on the TV
> in the UK a couple of weeks ago which seemed to indicate that the centre is
> actually solid, although around that it is molten.

Molten, but it's a composite material under a lot of pressure, so the 
transition between "liquid" and "solid" isn't like between ice and 
water.   Think cold peanut butter.

> I did not see it all and was only watching bits of it,  but it would appear
> some female researcher had proven this. The proof appeared to be based on
> the time of travel of shock wases from earthquakes and the different speed
> they travel through solid and liquid.

Seismic evidence is how they knew it was liquid in the first place.  As 
you get better at doing the models, and getting better time measurements 
of the seismic propagation with higher performance seismometers, you can 
get a better model.

Combine that with precise orbit determination (using accurate 
measurements of time and frequency from orbits) which allows accurate 
gravity models (e.g. GRACE and GRACE-Follow-On)

> Dave.
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