On Thu, Dec 07, 2023 at 11:19:19PM -0500, gene heskett wrote: > [...] a method for determining leap years. It was also > used in some astronomical programs for lunar and solar eclipses. This I > think was the reason that all unix times start at midnight 1/1/1970. In the > FWIW dept this time formula is pretty accurate back to the middle of 4713 > BC.
You're not actually talking about leap years, are you? Are you maybe talking about *Easter*? Or something involving the spring equinox? Also, the idea that a calculation of *anything* in our current Gregorian calendar system would extend back to a BC date is ludicrous, as the Gregorian calendar was not in use at that time. It wasn't invented until thousands of years later. Even the *Julian* calendar used in ancient Rome wouldn't have been in use in 4713 BC. Any calendar would have been locally defined, if one existed at all.
