Re: Concalendrical reference point

On Wednesday 29 May 2002 14:43, And Rosta wrote:
> Does this mean that if we factor out the culture-specific Roman
> tax calendar, leaving us with just solar and lunar cycles, that
> a combined solar and lunar cycle is 28 * 19 = 532 years?
>
> Is it possible to work out dates in the past when, say, the spring
> equinox and the corresponding lunar phase (I don't know what it's
> called, but will enjoy someone taking pleasure in informing me)
> happen on the same day at notionally the exact same moment? The
> idea is that this would serve to locate the boundaries between
> the 532-year cycles.
        Unfortunately, no. Consider why we are using the Gregorian calendar, rather
than the Julian calendar. A 532 year cycle wusing the Julian calendar would
gradually drift against the seasons. The point at which both the solar and
lunar cycles re-sync is some rather large number that I have been unable to
recollect at the moment. I think it may be in the range of 650+ years, but I
would not be surprised if that is incorrect. The basic problem is that the
length of the cycles change, thanks to gravity and entropy. The moon is
gradually moving away from the earth, and the earth's rotation is slowing
down; factor in the sun and it's a really nasty n-body problem.
        :Peter