<HTML>Dave Moore wrote:
[...]
> Avry
> (IIRC) was fond of quoting 25,776 years for the precessional
> cycle, but certainly, given the calculations needed, I
> personally would hesitate to use such an accurate figure.
> Steve Tonkin will know however, as he's in touch with that
> sort of thing... [1]
>
> Certainly when it comes to a discrepancy of a hundred of
> years or so in calculations as far back as 10500 BC, I think
> we can ignore such discrepancies...
I assume that was an invitation to contribute.
Dave is correct -- the uncertainty in the precessional period is less than a year, i.e. it's known to within 1/200000. Or, put another way, going back to 10500 BCE, the accuracy is to within a few months.
Similarly, the obliquity of the ecliptic can be determined to better than an arcminute precision up to about 25000 years ago. It get's a tad less precise beyond that. Up to about 5000 years ago it is precise to a few arcseconds.</HTML>
