see also: theAbysmal Calendar
lunar calendars, 365-day calendars, 364-day calendars, 363-day calendars, 361-day calendars
360 is such a marvellous number, as it can be divided in so many regular ways, and likely a larger number of irregular ones. In order to keep a 360-day calendar fixed to the Seasons, it requires the addition of 5 extra days, which are typically added at the end of the year.
World Calendars
As far as I’m aware, there are only a few 360-day calendars currently in use: the Coptic Christian and Ethiopian calendars, both of which are derived from the calendar of the Egyptians, and the Mesoamerican solar calendar, which, incidentally, does not observe a leap day.
Ethiopian & Coptic Calendars:
365 = 360 + 5 = 30 x 12 + 5
Maya & Aztec Calendars:
365 = 360 + 5 = 20 x 18 + 5
theAbysmal Calendar divides 360 days several ways, intended to accommodate a large number of market weeks.
Dividing 360
365 = 360 + 5 = 23 x 32 x 5 + 5
Weeks: 3-, 4-, 5-, 6-, 8-, 9-, 10-, 12-day
Longer Divisions: 180-day semester, 120-day term, 90-day quarter, 72-day fifth
The first calendar day of the 360-day system falls on Dec 22.
There are a few variations of skipped days, which don’t occur together at the end of the year like the Coptic and Mesoamerican calendars, but are distributed symmetrically to fall between months as follows:
360 A) Dec 21, Feb 5, May 7 (6 in a leap year), Aug 6, Nov 5
this applies to the 24- and 8-month calendars, and synchronizes with the Wheel of the Year, 365-day Binary Year as well as 364-day calendars.
360 B) Dec 21, Mar 4 (3), May 16 (15), Jul 28, Oct 9
this applies to the 20-, 15-, and 10-month calendars
these are the mid-fifth days of the 365-day year, and divides the 360-day year into even fifths of 72 days.
360 C) Dec 21, Feb 20, Apr 22 (21), Aug 21, Oct 21
this applies to the 12- and 6-month calendars.
360 D) Dec 21, Mar 12, (11), Jun 1 (May 31), Jul 12, Oct 1
this applies to the 18- and 9-month calendars.
A) 24-Month Year
This calendar is an analog to the 24-hour clock: the year begins at the Winter Solstice the way the clock begins at Midnight. This also ties in with the 24-day month of the 15-month year below. These months are also called hōra.
360 = 5 days x 3 weeks x 24 months
Weeks: 3-, 5-day
5 days x 3 weeks x 24 months – regular year
5 days x 3 weeks x 24 months – leap year
A) 8 Month Year
Like the 24-month year above, this calendar synchronizes with the Wheel of the Year, the Binary Year, and 364-day calendars.
360 = 9 days x 5 weeks x 8 months
Weeks: 3-, 5-, 9-day
9 days x 5 weeks x 8 months – regular year
9 days x 5 weeks x 8 months – leap year
B) 20-month year
360 = 6 days x 3 weeks x 20 months
Weeks: 3-, 6-, 9-day
6 days x 3 weeks x 20 months – regular year
6 days x 3 weeks x 20 months – leap year
B) 15-month year
The 24-day month is an analog to the 24-hour day and 24-month year.
360 = 6 days x 4 weeks x 15 months
Weeks: 3-, 4-, 6-, 8-, 12-day
6 days x 4 weeks x 15 months – regular year
6 days x 4 weeks x 15 months – leap year
360 = 8 days x 3 weeks x 15 months
8 days x 3 weeks x 15 months – regular year
8 days x 3 weeks x 15 months – leap year
B) 10-month year
The 36-day month provides a lot of options for subdivision.
360 = 9 days x 4 weeks x 10 months
Weeks: 3-, 4-, 6-, 9-, 12-day
9 days x 4 weeks x 10 months – regular year
9 days x 4 weeks x 10 months – leap year
360 = 12 days x 3 weeks x 10 months
12 days x 3 weeks x 10 months – regular year
12 days x 3 weeks x 10 months – leap year
C) 12-month year
This calendar divides the year like the Coptic and Ethiopian calendars do, 12 months of 30 days, which most closely approximates the lunar year.
360 = 6 days x 5 weeks x 12 months
Weeks: 3-, 5-, 6-, 10-day
6 days x 5 weeks x 12 months – regular year
6 days x 5 weeks x 12 months – leap year
360 = 10 days x 3 weeks x 12 months
10 days x 3 weeks x 12 months – regular year
10 days x 3 weeks x 12 months – leap year
C) 6-month year
These periods feel a little long to be called months, however, sixths is an unnecessarily spitty word to pronounce in English.
360 = 12 days x 5 weeks x 6 months
Weeks: 3-, 4-, 5-, 6-, 10-, 12-day
12 days x 5 weeks x 6 months – regular year
12 days x 5 weeks x 6 months – leap year
D) 18-month year
This calendar arranges the year like the Mesoamerican Haab’ and Xiuhpōhualli by creating months of 20 days.
360 = 5 days x 4 weeks x 18 months
Weeks: 4-, 5-, 10-day
5 days x 4 weeks x 18 months – regular year
5 days x 4 weeks x 18 months – leap year
D) 9-month year
360 = 8 days x 5 weeks x 9 months
Weeks: 4-, 5-, 8-, 10-day
8 days x 5 weeks x 9 months – regular year
8 days x 5 weeks x 9 months – leap year
360 = 10 days x 4 weeks x 9 months
10 days x 4 weeks x 9 months – regular year
10 days x 4 weeks x 9 months – leap year
Figurate Time
see: Figurate Time
Figurate numbers are used in mathematics to define geometric shapes. These can then be used to generate weeks of different lengths.
24 triangular months
360 = 24 x (1+2+3+4+5)
24 hexagonal months
360 = 24 x (1+5+9)
20 7-gonal months
360 = 20 x (1+6+11)
15 9-gonal months
360 = 15 x (1+8+15)
12 11-gonal months
360 = 12 x (1+10+19)
10 triangular months
360 = 10 x (1+2+3+4+5+6+7+8)
10 square months
360 = 10 x 62
10 13-gonal months
360 = 10 x (1+12+23)
9 octagonal months
360 = 9 x (1+7+13+19)
9 13-gonal months
360 = 9 x (1+13+26)
8 triangular months
360 = 8 x (1+2+3+4+5+6+7+8+9)
8 hexagonal months
360 = (1+5+9+13+17)
Rethinking Time 