[LEAPSECS] What happened in the late 1990s to slow the rate of leap seconds?

Brooks Harris brooks at edlmax.com
Mon Nov 9 09:15:29 EST 2015

Hi Steve,

I just wanted to compliment you on the huge about of work in these 
pages. Its a fantastic collection of facts and your explanations and 
commentary are extremely helpful. Well done and thank you.


On 2015-11-08 10:15 PM, Steve Allen wrote:
> On Sun 2015-11-08T18:51:37 -0800, Hal Murray hath writ:
>> Was there a geological incident that explains things?
> The crust of the earth has accelerated its rate of rotation during
> most of the past 100 years.  The slowest rotation ever was around
> 1912, and since then it has been rotating faster.  By happenstance,
> the rate of rotation of the crust was at a local minimum in 1972 at
> the inception of leap seconds, and since then it accelerated again.
>> There is another warp in the graph in the late 1980s.  Things slowed down for
>> several year, but not as dramatically as the early 2000s.
> Don't look at the graph of Delta T, that's effectively the integral of
> the rate of rotation and its smoothness hides what the slope is
> telling you.  Look at the graph of Length of Day.  That
> integral/derivative pair are the first two graphs at
> http://www.ucolick.org/~sla/leapsecs/amsci.html
> For a historic view of the LOD going back 2000 years look at the plots on
> http://www.ucolick.org/~sla/leapsecs/dutc.html
> --
> Steve Allen                 <sla at ucolick.org>               WGS-84 (GPS)
> UCO/Lick Observatory--ISB   Natural Sciences II, Room 165   Lat  +36.99855
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