Basic formulas for programmable calculation of celestial calendar dates

Calculation methods for converting calendar dates into Julian dates and vice versa are presented for several secular astronomical calendars. The use of computer programs for microcomputers and pocket calculators is discussed and the difficulty in finding a universal program for the different calendar types is emphasized. Equations for converting the Gregorian, Egyptian, Persian, and Islamic calendar dates into Julian calendar dates are presented. Attention is given to three suggestions for possible calendars: (1) the International Fixed calendar of 13 months of 28 days, (2) the World calendar with 12 months of 31, 30, and 30 day quarters, and (3) the Perpetual calendar with 30, 30 and 31 days in each quarter year.