[LEAPSECS] The relation between calendars and leap seconds.

[Tony Finch]

On Mon, 10 Nov 2008, Peter Bunclark wrote:

> On Mon, 10 Nov 2008, Tony Finch wrote:

> >

> > On Sun, 9 Nov 2008, Peter Bunclark wrote:

> > >

> > > So a User requirement might be:

> > > The rythms of life, including the orbits of the earth and the moon,

> > > the rotation of the earth, and convenient sub-divisions of the rotation

> > > down to nearly the limit of human perception, shall be expressed in

> > > a single monotonic calendar.

> >

> > I guess you mean the limits of human perception as assisted by suitable

> > tools...

>

> No. Tools evolve a lot more quickly than we do.  I had around 1s in mind.


But unassisted human perception can't tell the time of day to 1s accuracy.

Perhaps I misunderstood you and you meant this to be a requirement on the
resolution of time measurements, and not (as I understood) some statement
about using the best available technology used to make those measurements.
If so that doesn't get us any further than the state of the art 100-200
years ago.


> We have months, which are lunar-ish.


They don't express the orbit of the moon, so they don't satisfy your
requirement.


> Again, I tried to be as timeless as possible.


You have to be careful that timeless requirements (haha) are not going to
be undermined by changes in technology. For example, there's no problem
dividing a day into 86400 equal seconds if you can't measure time
accurately enough to detect variations in the length of a day. If you need
the kind of accuracy you get from atomic time, you cannot satisfy the
requirement for equal subdivisions of a day.

While we are taking a historical view of calendars, it's probably worth
observing how past problems similar to the current situation have been
resolved. UTC is an observational calendar, and over history these have
almost always been replaced with arithmetic calendars: this eliminates
problems of communication from the observers who determine the calendar to
its users, gives users more independence and allows them to make more
accurate plans for the future, at the cost of a smallish error that makes
future dates drift away from the events they were previously attached to.
Calendars get reformed if they are not sufficiently predictable. This is
happening now to UTC, which seems to be the result of a timeless human
factors requirement in action.

I agree with your requirements 2,3,4 and I note that UTC doesn't satisfy
3, which is another statement of this timeless predictability requirement.
(Your requirement 4 is only relatively timeless, since it allows for
changes in the definition of the second.)

Tony.
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