[LEAPSECS] Consensus building 2

[Tony Finch]

On Thu, 3 Feb 2011, Stephen Colebourne wrote:

>

> * TAI-2008 does not definitively imply a definition for minutes, hours and days


Yes it does, since the usual way of writing a TAI instant is in ISO 8601
format.


> * definition: solar-time - time kept or measured by the Sun


time measured by the rotation of the earth relative to the sun.


> * the accurate measurement of solar-time is complex and typically

> achieved via cooperation


How accurate? Does a precision sundial not count? What about a clock
regulated by a transit instrument?

Since you say this for every form of time it sounds like a redundant
platitude.


> * the length of a mean-solar-day in in SI-seconds varies over time

> * the length of a mean-solar-day in in SI-seconds is on average

> increasing with time

> * the length of a mean-solar-day is not a fixed number of SI-seconds


This last definition is redundant. (There's a similar redundancy for UT1.)


> * definition: UT - a time scale based on the rotation of the Earth

> (defined in detail elsewhere)


based on the rotation of the Greenwich meridian relative to the Sun.
(The specific meridian is what distinguishes it from solar time in
general.)


> * definition: UT1 - a smoothed variant of UT (defined in detail elsewhere)


Mean solar time for the Greenwich meridian.


> * the UTC-1972 time-scale is a continuous count of SI-seconds


It uses TAI seconds.

The number of seconds in a UTC interval cannot be deduced from the
standard representation of the start and end UTC instants without the
assistance of an auxiliary table of leap seconds.


> - a humanity-day is interpreted in line with the rising and setting of the Sun


Except in tricky situations like transcontinental flights and living near
the poles.


> * a UT1-day is the most commonly recognised form of a humanity-day


Definitely not, because of DST.

Tony.
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