Re: CHAT: Passover

> Date:         Wed, 26 Apr 2000 20:10:37 -0400
> From: Nik Taylor <fortytwo@...>
>
> Lars Henrik Mathiesen wrote:
> > The definition I was taught is that Easter Sunday is the first Sunday
> > after the first full moon after the vernal equinox.
>
> Close - the first Sunday after the first full moon *on or after* the
> vernal equinox.  The official full moon can occur on March 21, but
> Easter cannot, because Easter cannot be on that full moon.
>
> Of course, in reality, the full moon and vernal equinox are not used,
> but merely calculated.  Thus, it's conceivable that a full month could
> occur between what astronomical observation would indicate and the
> calculation, since both the actual vernal equinox and the actual full
> moon can vary a day or so from the calculated point.
Understand that I'm only playing around with what would happen if
everybody defined the dates of equinoctes and full moons according to
astronomy and their local time.

The scenario now looks like: Full moons at Saturday March 20 20:30 UTC
and Monday April 19 09:13 UTC, with spring equinox occurring at Sunday
March 21 04:30 UTC.

        time zone       equinox         Ea. full moon   Easter Sun
        +13 to +4       Sun Mar 21      Sun Mar 21      Sun Mar 28
        +3 to -4        Sun Mar 21      Mon Apr 19      Sun Apr 25
        -5 to -11       Sat Mar 20      Sat Mar 20      Sun Mar 21

Now throw in DST and cultures for whom the date changes at local
sunset, and you'll have a right mess.

> > The same can happen with any observation-based methods of determining
> > the dates of equinox and full moon, of course. So it really does make
> > sense to fix a meridian, if only to know when 'Sunday' starts.
>
> If you want unity in celebration, certainly.  But, that's not used for
> Easter.
I'm not sure exactly what 'that' refers to here. Within each church
there _is_ unity in celebration---Easter falls on the same date---
because the calculations used for equinox and full moon give dates,
not UTC times, making the local time zone irrelevant.

But where I came in, someone (I lost track) was talking about a
proposed new Easter calendar that would be based on astronomical
events or even observation.

Lars Mathiesen (U of Copenhagen CS Dep) <thorinn@...> (Humour NOT marked)