[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

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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