On 02/02/2011 09:03, Stephen Colebourne wrote:
On 2 February 2011 15:33, Finkleman, Dave<[email protected]> wrote:
I suggest that the terms second, minute, hour, day, and month stated
without qualification have "normative" status: the SI second, 60 SI
seconds, 3600 SI seconds, 86,400 SI seconds, and Gregorian calendar
numbers of days expressed as 86,400 seconds.
Funilly enough, I'll start by disagreeing with those definitions. The
meaning of the things named "second" and "day" being key, the best
that consensus will agree to is precise definitions, rather than any
"land grab" of key terms.
The only consensus possible here is that 'seconds is an overloaded term
for both the length of time for so many CS atom oscillations, for the
amount of time the earth takes to rotate though 1/86400th of its
rotation, for 1/86400th of the average period of time it takes for earth
to rotate averaged over a year, and for 1/8400th of the average period
of time it takes the earth to rotate with various seasonal effects
included.' this corresonds to TAI/UTC, UT, UT1 and UT2 respectively.
This stems from a fundamental disagreement about time. Should it tick
off a fixed set of time, or should it tick off based on observations?
TAI is the latter, UT, UT1 and UT2 are different ways of account for the
former. UTC tries to split the baby and do both. There is a divergent
opinion bout which one people generally want to do because today the
difference between them falls well below the threshold of observable
effects on the human psyche. Humans are able to adopt to fairly large
difference between clock on the wall time and apparent solar time, but
there's no agreement as to how big this divergence can be, and the best
ways, if any, to keep things from drifting as well as being off today.
Until the fundamental disagreement is resolved, you aren't going to be
able to define these basic terms.
The terms SI-based-minute, SI-based-hour and SI-based-day will, I
suspect be acceptable to all. At the end of the process, the
defniition of the simple terms can then be considered.
Statements:
- an SI-based-minute is formed from exactly 60 SI-seconds
- an SI-based-hour is formed from exactly 60 SI-based-minutes and thus
exactly 3600 SI-seconds
- an SI-based-day is formed from exactly 24 SI-based-hours and thus
exactly 86400 SI-seconds
Even those statements aren't completely right. If you are in a TAI
frame of reference, they are right.
However, in a UTC frame of reference, they are all wrong. Minutes are
60 SI seconds, except when they are 61. Hours are 3600 SI seconds,
except when they are 3601. Days are 86400 SI seconds, except when they
are 86401.
Also, what is meant by mean solar X? what is the averaging time? what
are the requirements for smoothing?
Anything else requires qualification such as: mean solar seconds.
Actually I can't think of other forms of hour, day, etc. that require
qualification, since those are neither fundamental time intervals nor
time scales.
Defining things that are *not* fundamental time intervals nor time
scales is key to the problem.
The problem is very fundamental about what time should be.
Warner
I'll resend in the main thread an updated list so far.
Stephen
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