In case folks haven't noticed, Steve and I have each (separately) been
trying to talk about new topics (or, at least, new facets of old
topics :-)
Meanwhile...Poul-Henning Kamp replies:
The heart of civil timekeeping is the dynamic tension between the
two definitions of the "second":
- as 1/86400 of a mean solar day, and
- as the SI unit of time
I have still not found where the first definition have any
importance in civil timekeeping, apart from sundials. Can you give
more detail ?
Look back at a hundred arguments in a thousand emails. The "day" is a
key concept in our civilization. The "mean solar day" is the natural
way to implement this. Sundials have nothing to do with the mean
solar day, but rather the apparent solar day. Apparent solar time has
nothing to do with either UTC (as we currently know it) or TAI.
The problem at the heart of civil timekeeping is that the rules for
counting time are only known for the next six months at any one time.
My colleague, Dr. Steve, and I perceive the heart, you perceive a
narrowly construed pathology. Your stethoscope is tuned to the murmur
and you aren't hearing the healthy heart sounds (http://en.wikipedia.org/wiki/Heart_sounds
). lub dub...lub dub...lub dub
The solution to your problem won't become evident until you perceive
the beating heart of the larger design. To stress the analogy perhaps
a little too far, the ITU is about to sew up the patient's chest
cavity with the forceps still inside.
In any event, there are lots of things you will need to know in six
months that are hidden from you today. Addressing such issues is
simply a requirement placed on whatever systems are involved.
How we count, what we count and what it adds up to in the long run,
is totally without relevance in this picture, the problem is,
crudely put, that we know how many seconds there are in the next six
months, but not the next 12 months.
And that is because you are confusing two different meanings of time,
that is, of the word "second".
It's not the seconds, it's how we count them.
Put your O-O glasses on. It is BOTH the attributes AND the methods of
the class called "civil time".
Rob Seaman
NOAO
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