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13 month sol calendar

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