Warp  wrote in message <45c5ef88@news.povray.org>:
>   I think that mathematical interpolation of the movements of the Earth
> should give pretty accurate values for tens of thousands of years.

Except that it it not possible to interpolate, only to extrapolate, which is
much less accurate.

>   The problem with current calendars is that they are linear while the
> rotation of the Earth is not constant (which would require a non-linear
> calendar system). Linear calendars are acceptably accurate for only a
> few thousand years. If you want a calendar which is accurate to a fraction
> of a second for tens of thousands of years, you have to use a non-linear
> timeline (because of the slowdown of the Earth).

The computation system I was referring to, SMART97, is not linear at all. It
uses Poisson series, with thousands of terms.

The movement of Earth on its axis is just too complex to be computed
accurately over large periods of time.

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