THE 13 MONTH SOL CALENDAR


   Configuration:

        * Twelve contiguous and identical months of exactly 28 days.  
        * The last, thirteenth month of the year (December) has 29 days 
          normally and 30 days in a leap year.  
        * The new month (Sol) occurs between June and July.

   Features:

        * Avoids the use of intercalary days and the disruption of the
          standard week.  
        * Implementations the 13 period financial calendar already in wide 
          use in business and accounting.  
        * Placing the new month (Sol) at mid-year minimizes the seasonal 
          displacement of the traditional months.  
        * Placing the extra day(s) year-end allows all months to be identical 
          for their first 28 days in any given year.
        * Although not perpetual, the calendar does offer an easy method for 
          date/day calculations.

   Simple Calculations:

      To calculate any day or date in a given year you only need three bits
      of information.  First, what day of the week did January 1st fall on? 
      Secondly, is this a leap year?  Lastly, remember the numbers 1, 8, 15
      and 22 (1, 1+7, 1+14, 1+21).

      Let's assume January 1st was a Friday and it's a leap year. That means
      that the first, eighth, fifteenth and twenty-second day of every month
      is a Friday.  The twenty-ninth day of December (1+28) is also a Friday
      and, since it's a leap year, Saturday the 30th is the last day of the
      year.  The calculations are simple enough to do in your head:

      What is the third Monday in May? - Again assuming January 1st was a
      Friday, the third Friday in any month is the 15th so, with a bit of
      addition on our fingers, we discover the third Monday is the 18th. 
      What day of the week is August 13th?  Well August 8th is a Friday (as
      is August 15th) so with a bit more finger work, either adding or
      subtracting, we deduce the date is a Wednesday.


   Calendar Examples:

   06
   Mo Tu We Th Fr Sa Su
                     1
   2  3  4  5  6  7  8
   9  10 11 12 13 14 15
   16 17 18 19 20 21 22
   23 24 25 26 27 28 29


   07
   Mo Tu We Th Fr Sa Su
   1  2  3  4  5  6  7
   8  9  10 11 12 13 14
   15 16 17 18 19 20 21
   22 23 24 25 26 27 28
   29


   08
   Mo Tu We Th Fr Sa Su
      1  2  3  4  5  6
   7  8  9  10 11 12 13
   14 15 16 17 18 19 20
   21 22 23 24 25 26 27
   28 29 30

   

      Jim Eikner (2006)

      Creative Commons License
      This work is licensed under a Creative Commons
      Attribution-Noncommercial-Share Alike 3.0 License.