VMs: Re: Random discoveries in the library

[Jorge Stolfi <stolfi@xxxxxxxxxxxxx>]

    > I cannot find a single copy of this figure on any
    > of my old pages. Even the photocopy has gone missing.
    > I know that Dennis had a copy too, for a while, and
    > somewhere in the mailing list archive there is a
    > reference to another web page with the same figure
    > stating it is actually part of the VMs. (Jim Reeds
    > found that one).

It took some searching, but I found a copy of it in my cache of
Voynichanea (which is sort of like my desk, only several orders of
magnitude bigger):

  http://www.ic.unicamp.br/~stolfi/voynich/misc/rene-astro-diag.gif
  
    > the [symbol] for Aries (a V with an under- score) looks exactly
    > like the first red doodle on VMs f1r.

Yes.  The VMS author must have thought so too. ;-)

    > Didn't Gauss (well post-VMs) invent a way to predict
    > the dates of Easter using a method involving
    > prime numbers, a.o. 17?
    
Hmmm... Well, the usual algorithm is based on a *19* year cycle. It
uses other divisors, but mostly to account for leap years and the
Gregorian change, and to find the month and day-of-week:

    http://aa.usno.navy.mil/faq/docs/easter.html

    c = y / 100
    n = y - 19 * ( y / 19 )
    k = ( c - 17 ) / 25
    i = c - c / 4 - ( c - k ) / 3 + 19 * n + 15
    i = i - 30 * ( i / 30 )
    i = i - ( i / 28 ) * ( 1 - ( i / 28 ) * ( 29 / ( i + 1 ) )
        * ( ( 21 - n ) / 11 ) )
    j = y + y / 4 + i + 2 - c + c / 4
    j = j - 7 * ( j / 7 )
    l = i - j
    m = 3 + ( l + 40 ) / 44
    d = l + 28 - 31 * ( m / 4 )

The algorithm may be due to Gauss, but knowledge of the 19-year cycle
is certainly much older.

All the best,

--stolfi