Jos Kint asks:
> Has anyone an idea how to use a sundial for calculating if the current year
> is a leap year? And, if not, how many years we are behind the next leap year?
Probably not the answer you're looking for, but see p. 6 of:
http://futureofutc.org/2011/preprints/10_AAS_11-665_Hillis.pdf
A mechanical clock realized as a digital computer, the 10,000-year clock can
also be regarded as a fancy sundial since its solar synchronizer is used to
reset it every clear day. (Over 10,000 years it is expected there will be
periods when clear days are separated by several years, e.g., if the
supervolcano under Yellowstone goes off.)
Once you have a reliable time signal as input to a digital computer, the
computation of the Gregorian calendar is straightforward (as long as the clock
is never allowed to stop - and a future Pope doesn't revise the calendar). The
10,000-year clock is being built into a mine shaft 500 feet high, but there is
no reason a smaller sundial couldn't be coupled with a computer.
For proof of concept, imagine a solar cell connected to a microprocessor
powered by a rechargeable battery. Sunlight would both keep the battery
charged and present a diurnal input to the CPU to correct the internal clock.
Like I said, not what you're looking for.
If not a digital clock, one would need the equivalent analog clock. The
diurnal signal remains the most obvious to tap into (certainly for a sundial),
and your word "calculating" implies some sort of mechanism, however realized,
for accumulating days into years and performing modula arithmetic on the years.
The equation of time built into a sundial (or the 10,000-year clock) couples
the diurnal waveform to an annual waveform. Or via ever more faint orrery
signals to astronomical rhythms of the planets, etc.
Writ large, these mechanisms are monuments like Stonehenge, pyramids, etc.
(Though presumably the astronomical nature asserted for some of these is
spurious.) The computers in these installations were human acolytes, tending
to the associated ceremonies commensurate with the natural cadences.
I suppose one could imagine pegs built into a sundial like a cribbage board,
coupled with a simplified set of rules for moving the pegs given daily or
annual milestones. In some sense this is no different than moving a gnomon to
subsequent days on an analemma:
http://futureofutc.org/2011/friday_tour.html
Rob Seaman
National Optical Astronomy Observatory
Tucson, AZ---------------------------------------------------
https://lists.uni-koeln.de/mailman/listinfo/sundial
