[ntp:questions] Leap second functional question

Unruh unruh-spam at physics.ubc.ca
Tue Feb 26 12:36:36 UTC 2008

```ddunham at taos.com (Darren Dunham) writes:

>Unruh <unruh-spam at physics.ubc.ca> wrote:
>>>> 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
>> They are
>>>which case a leap second won't be needed. If it is systematic,
>> They would still be needed. Just because your computer's drift rate is both
>> positive and negative does not mean that compensation is not needed.
>> They do not necessarily average out on the time scale of years.
>>
>> There is a net drift to longer days. but superposed on that is a noise
>> which even over the time scale ofyears makes a difference. An earthquake in
>> Java rearranges the moment of inertia of the earth and changes the rotation
>> rate of the earth, and it can be positive or negative.
>>
>>>i.e. the changes are more in one direction than another, a leap second
>>>will be needed.
>>
>> It is needed even if it equal in both directions over a long time.

>It is needed if the noise is equal in both directions *and* if the
>average is somewhere near zero.

>Besides the noise, there is a strong forward bias as well.  The second
>is based on earth rotation in 1900.  The past century has allowed for
>the average rate to slow significantly since then.

>So a negative leap will only be needed if the noise is strong enough to
>wipe out the entire bias.  The recent speedup has only been strong
>enough to delay the positive second additions, not reverse them.

Yes. And? All you would need is twice the recent speedup and you would get
a decriment. It may not happen, but then again it may.

><http://en.wikipedia.org/wiki/Image:Leapsecond.ut1-utc.svg>
><http://maia.usno.navy.mil/lplot1.gif> (Excess Length of Day plot).

```