[LEAPSECS] Do good fences make good neighbors?

[Joe Gwinn]

At 3:03 PM -0700 1/14/11, Rob Seaman wrote:

>On Jan 14, 2011, at 2:40 PM, Poul-Henning Kamp wrote:

>

>>  In message <F1C36C4F-A32A-4EBB-BFDE-C51C8A156557 at noao.edu>, Rob 

>>Seaman writes:

>>

>>>  My answer has always been that both are necessary.  Leap seconds 

>>>are one possible way to reconcile these very different flavors of 

>>>time.

>>

>>  They are not different flavors of time, one is a measurement of 

>>time, the other a measurement of speed of rotation.

>>

>>  Both are needed, for sure, but that does not make the both 

>>measurements of time.

>

>If you wish.  In that case, note that sexagesimal notation is used 

>for angles, while systems like Unix often express "measurements of 

>time" intervals as unending counts of seconds (SI or otherwise) 

>since some epoch.  That epoch, eg midnight 1 Jan 1970, was itself 

>selected as representing an angle related to the Earth.


UNIX chose 00:00:00 GMT 1 January 1970 as their epoch simply to be 
synchronized with civil time, at least initially.  In IEEE 
1003.1-1988 (the Ugly Green POSIX.1 standard), this became 00:00:00 
UTC 1 January 1970, as GMT had been replaced, at least in California. 
But the UNIX/POSIX folk cared little about angles.  Nor is POSIX time 
UTC, even though the epoch is defined in UTC: there are no leap 
seconds in POSIX time.   POSIX time is in theory a form of TAI (and 
thus is independent of Earth rotation), but in practice is whatever 
GPS and NTP say it is (and will follow leap seconds to the degree the 
chosen GPS and NTP do).

In any event, POSIX time is not an argument for or against any of the 
debated leapsecond proposals.

Joe Gwinn