[ntp:questions] Leap second functional question

Unruh unruh-spam at physics.ubc.ca
Fri Feb 22 01:29:07 UTC 2008


Greg Hennessy <greg.hennessy at localhost.localdomain> writes:

>On 2008-02-20, Unruh <unruh-spam at physics.ubc.ca> wrote:
>> No orbital dynamics obeys Newton's ( or Einstein's) law of gravitation only
>> in TAI not in UTC ot UT1.

>High precision orbital dynamics, such as the JPL's DE405, are done in 
>Barycentric Dynamic Time, which runs at a different rate than TAI, but
>is "TAI like" in that it has no leap seconds.

It does? The second was defined to make the speed of light a consant. Are
you saying they use a system in which the speed of light changes from time
to time? That sounds horrible. 


>> Of course I cannot. Leap seconds are to take into account the random
>> variations in the earth's rotation to one part in about 10^8. 

>Leap seconds take into account the systematic slowing of the earth's
>rotation. 

While it may be slowing on average, it is noise and it could well speed up
as well. For example there have been no leap seconds for the past 4 years
or so, while the "aveage slowing would have one every 1.5 to 2 years right
now. Ie there has been a speedup against the average recently






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