The Gregorian Interface
Converting dates between the Jewish and Gregorian calendars is a rather major challenge. Adding to that challenge is the fact that every small amount of millennia an unusual adjustment has to be made to the Gregorian calendar. The same is true with the Jewish one as well. This is because the two calendars are not absolutely perfect in keeping "in sync" with the exact solar year. It takes the earth 365 days, 5 hours, 48 minutes and 46 seconds (approximately 365.2422 days) to complete what is known as a tropical orbit around the sun. Fortunately (at least based upon what I have come across so far), as far as Jewish-Gregorian conversions are concerned, this shouldn't present a problem from the Jewish year 1 up to well past the Gregorian year 2000 CE, except that a Gregorian adjustment in 1582 CE (elimination of a period of ten days in October from the 5th to the 14th) has to be accounted for. I have yet to check for other possible adjustments (pre-1582 CE). I also am not sure of the time zone that the molad refers to, but if I had to guess, it would probably be Jerusalem Standard Time.
One of my earlier programs, a Jewish year evaluation utility, is provided below. It gives some information about such a year. Enter an unsigned integer for the year (up to 4 digits). There is the option of entering a Gregorian year (from which the Jewish will be determined). If a Gregorian year before the Common Era is to be used, simply enter the number of that year, and select the Before Common Era entry (make sure that the Gregorian entry is selected as well). PLEASE NOTE: This uses the system that places the year 1 CE immediately after 1 BCE (no intervening "year 0"). This means that while Rosh Hashanah for the Jewish year 3762 took place during the Gregorian year 1 CE, Rosh Hashanah for the Jewish year 3761 (not 3760) took place during the Gregorian year 1 BCE. Thus valid Gregorian BCE years for this utility are 1 through 3761.
The above utility uses CGI (Common Gateway Interface), which I started getting involved with back in the late 1990's CE.
Provided in the next section is a long-awaited utility which I have more recently developed—an informative Gregorian-Jewish date converter!
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