Re: Calendrical Module

[Craig Markwardt <craigm(at)cow.physics.wisc.edu>]

bouncenews@contessa.phone.net (Mike Meyer) writes:
> 
> Out of curiosity, was the patent applied for before or after the first
> publication of these algorithms? If it was after, then they won't be
> able to get a patent outside the US (last time I looked, anyway). That
> would make the world of date/time calculations almost as interesting
> as the one of cryptography...
> 
> 	<mike

Pardon my lurking, but I would like to mention that astronomers have
certainly been concerned about calendar date conversions, at least
from a historical perspective.  Astronomers typically convert back and
forth between Julian Days, since they are a useful, continuous
represetation of the calendar, but historical astronomers also need to
know how to convert the calendar systems of the ancients.

Here are two references to published algorithms, which appear to
predate the Reingold work.

Hatcher, D. A., "Simple Formulae for Julian Day Numbers and Calendar
Dates," 1984 Quarterly Journal of the Royal Astronomical Society, 25,
53-55.

Hatcher, D. A., "Generalized Equations for Julian Day Numbers and
Calendar Dates", 1985 Quarterly Journal of the Royal Astronomical
Society, 26, 151-155

The articles are very short, and have an elegant calendar date
conversion algorithm.  The second paper is more general, and includes
coefficients for various calendar systems, including the Egyptian,
Alexandrian, Roman, Gregorian, and Islamic.

Craig

-- 
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Craig Markwardt, Ph.D.              
EMAIL: craigmNOSPAM@lheamail.gsfc.nasa.gov 
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