>
> In article <Pine.LNX.3.95.980622082303.1910B-100000@chaos.analogic.com> you wrote:
> > On Sat, 20 Jun 1998, Rogier Wolff wrote:
>
> >> The gregorian calendar will be off-by-a-day after about 51395 years.
> >> This does not take any "slowing" effects into account.
>
> > Isn't this the reason for the "leap-second" thrown in every so often
> > by the regulatory authorities (NIST in the USA)? I understand that
> > the number of days in a year has been adjusted by convention, to be
> > some number that is exactly represented. The result is adjusted to
> > be, on the average, correct by use of the leap-second.
>
> There's a mistake in there somewhere. The leap second adjusts for
> variations in the length of a day (ie the time it takes for the earth
> to spin around its own axis). It cannot adjust for the length
> of a year (ie the time it takes (in days!) to orbit the sun once).
>
You can't measure the length of a year with a different kind of 'second'
than you measure the length of a day. If you try, the vernal equinox and
autumnal equinox (equal day/night time-line) will shift. This will cause
the months to lose synchronization with their true position relative to
the sun.
The earth does not rotate in exact synchronization with its orbit around
the sun. In other words, it does not make an integral number of rotations
during its trip. Instead, a point on the surface of the earth moves
across a fixed point in space every approximately 22 years.
The whole yy:mm:dd:hh:mm:ss ball of wax must be synchronous. At
last reading, this was done by "Convention", i.e., international
agreement. The drift of Earth time from Celestial time is periodically
taken out by leap-seconds.
Cheers,
Dick Johnson
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