Re: slowing down the earth's spin

[David Bowman <dbowman@TIGER.GEORGETOWNCOLLEGE.EDU>]

Regarding Carl Mungan's question:

> > The actual moment of inertia of the Earth about its spin axis is much
> > closer to I = 0.33078*M*R^2 where R is the equatorial radius.
>
> How was this value obtained? From a model of the earth or from some
> timekeeping kind of measurement?

I don't know how the value was obtained.  I obtained it from an
online lecture for a geological science course at U. Mich.
(http://www-personal.umich.edu/~youxue/GS114.11.pdf).  Since finding
this value I snooped around a little bit more on the net and found
other values (of possibly dubious authority) that differ a little
from this one (& each other) in the 4th sig fig.  I suspect that
maybe NASA, USGS, NIST, or some other such outfit by have the
definitive value on line somewhere.

My suspicion (and only that) is that possibly the result was obtained
from observations of anomalies in the orbits of satellites combined
with the observed spin precession of the Earth in the mean
solar-lunar gravitational field gradient.

David Bowman

This posting is the position of the writer, not that of SUNY-BSC, NAU or the AAPT.