length of day

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From: Paul Doherty (pauld@exploratorium.edu)
Date: Thu Dec 30 2004 - 09:25:16 PST

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Message-Id: <l03110726bdf9e7f6140c@[192.168.112.4]>
Date: Thu, 30 Dec 2004 09:25:16 -0800
From: Paul Doherty <pauld@exploratorium.edu>
Subject: length of day

Here is a plot of the variation of the length of the day over the last few
years.

http://lupus.gsfc.nasa.gov/global/lod1102g.gif

The variations are on the order of 1 millisecond.(1000 microseconds)
The change in the length of the day due to the earthquake is predicted to
be 3 microseconds. So it might take a while to separate this small signal
from the large background. (But I'm still betting that it will be done.)

The expected change in the direction of the earth's axis is 0.8
milliarcseconds,
VLBI (Very long baseline interferometry) can measure positions to 0.1
milliarcseconds, so this should be measureable.

Here is a 1997 article on the phenomena affecting the length of the day and
the direction of the rotation axis.

http://lupus.gsfc.nasa.gov/core/final1.html

Paul Doherty

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