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 <[email protected]>, 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
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