Calendar Wiki

Dr. Irv Bromberg of the Univerity of Toronto has developed two leap week calendars, called the Symmetry010 Calendar and the Symmetry454 Calendar.  The Symmetry010 Calendar uses months with the lengths of 30-31-30–30-31-30–30-31-30–30-31-30/37(ly).  The Symmetry454 Calendar has months whose lengths are 28-35-28–28-35-28–28-35-28–28-35-28/35(ly).  But, he uses the names of the current months of the Gregorian Calendar for the names of the months in both Symmetry Calendars.  This can cause some confusion when trying to determine to which calendar the given date refers.        

To help alleviate this confusion, Walter Ziobro proposes the use of unique alternate month names for use in both of his Symmetry calendars.  The base of each name is derived from the corresponding Gregorian month name.  For months in the Symmetry010 Calendar, the endings indicate the position within each quarter, and the weekday which starts that month.  For the Symmetry454 Calendar, the endings indicate in which quarter the month occurs, and are derived from the endings used in the French Republican calendar. (Credit goes to Karl Parlmen for suggesting these naming conventions.)

In Dr. Bromberg’s Kalendis program, either Symmetry calendar can be used with several different leap week rules.  In the interest of synchronizing the Symmetry Calendars with the ISO 8601 week dating system, Ziobro uses the rule that adds the leap week in a year that has 53 ISO weeks.  Unique 3-letter abbreviations are in parentheses: 

 Alternate month names for Sym010/454
MM QM Symmetry010  Symmetry454
Name Abbr Days Start Name Abbr Days Start
01 Q11 Janum   (Jam) 30  W01-1 Janose (Jao) 28  W01-1
02 Q12 Februm (Fbm) 31  W05-3 Febrose (Fbo) 35  W05-1
03 Q13 Marcha (Mra) 30  W09-6 Marchose (Mro) 28  W10-1 
04 Q21 Aprilum (Apm) 30  W14-1 Aprial (Apl) 28 W14-1
05 Q22 Mayum (Mym) 31  W18-3 Mayal (Myl) 35 W18-1
06 Q23 Juna (Jna) 30  W22-6 Junal (Jnl) 28 W23-1 
07 Q31 Julum (Jlm) 30 W27-1 Julidor (Jld) 28  W27-1
08 Q32 Augustum (Aum) 31  W31-3 Augidor (Aud) 35 W31-1
09 Q33 Septa (Spa) 30 W35-6 Septidor (Spd) 28  W36-1 
10 Q41 Octum (Ocm) 30  W40-1 Octaire (Ocr) 28  W40-1
11 Q42 Novum (Nvm) 31  W44-3 Novaire (Nvr) 35  W44-1
12 Q43 Deca (Dca) 30/37 W48-6 Decaire (Dcr) 28/35  W49-1 

See also[]