[ntp:questions] Leap second functional question

Greg Hennessy greg.hennessy at localhost.localdomain
Fri Feb 22 03:23:26 UTC 2008

On 2008-02-22, Unruh <unruh-spam at physics.ubc.ca> wrote:
>>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. 

I am saying that high precision orbital dynamics are done from the
reference frame of the solar system, which we call the barycentric
frame. The barycentric time rate is different from that of TAI by a
factor of about 1e-15 if I remember correctly. 

> While it may be slowing on average, it is noise and it could well speed up
> as well.

Noise implies that the changes are both positive and negative, in
which case a leap second won't be needed. If it is systematic,
i.e. the changes are more in one direction than another, a leap second
will be needed.

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