User:Jc3s5h/extreme date conversion

The Gregorian dates below were calculated using the knowledge, derived from the United States Naval Observatory Multiyear Interactive Computer Almanac that noon, Universal Time, 25 February 1996 is Julian date 2,450,139. In addition, Gregorian dates, days of week, and leap year status repeat after 400 years and 400 Gregorian years contain exactly 146,097 days. Julian calendar dates were obtained by entering the calculated Julian date into the website https://www.fourmilab.ch/documents/calendar/

The year sign convention for INPUT JULIAN YEAR OUTPUT GREGORIAN YEAR and is that there is no year 0 and -4714 means 4714 BCE, as in versions of ISO 8601 before the 2004 revision, and certain software who's authors were foolish enough to read ISO standards. This convention is contrary to the convention of astronomers since 1740.

There is a correction contained in JulianDateTimeValueCleaner to follow the convention followed by astronomers and ISO 8601:2004. This correction is not incorporated in this table. A simplified version of JulianDateTimeValueCleaner was created which could be run on the Windows command line to test the cal_to_jd and jdtogregorian PHP functions, without the negative year convention correction.