[LEAPSECS] Consensus building 2
dot at dotat.at
Thu Feb 3 05:45:02 EST 2011
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
> * 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
> * 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
> * 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
> * a UT1-day is the most commonly recognised form of a humanity-day
Definitely not, because of DST.
f.anthony.n.finch <dot at dotat.at> http://dotat.at/
HUMBER THAMES DOVER WIGHT PORTLAND: NORTH BACKING WEST OR NORTHWEST, 5 TO 7,
DECREASING 4 OR 5, OCCASIONALLY 6 LATER IN HUMBER AND THAMES. MODERATE OR
ROUGH. RAIN THEN FAIR. GOOD.
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