A perennial solar calendar based on astronomical observations.

The calendar year consists of 360 calendar days + 5 or 6 intercalary days. It is divided into 4 equal quarters of 1 intercalary day + 90 calendar days. The remaining 1 or 2 days of the year are intercalary transition days between years.

The 360 calendar days may be divided into 8 months of 45 days, as well as 40 weeks of 9 days (3 × 3, based on tridays). Alternatively, one can use the more traditional 12 months of 30 days and a 7-day week. A zero-indexed variant based on the 9-day week is also possible. See Variants for more.

The calendar year begins at the midnight closest to the instant of the northward equinox as measured from the prime meridian. Consequently, if the northward equinox falls before solar noon on a particular day, then that day is the first day of the year. If the northward equinox occurs after solar noon, the following day begins the calendar year.

The calendar's proposed epoch is the beginning of the human era (10001 BC).

Essentially, it's the Persian calendar with a different epoch, a different meridian and a different division of the year. The calendar and its astronomical basis is deeply indebted to Persian astronomer Omar Khayyam's 11th century reform of the Jalali calendar.

For more details, see the calendar's project page.

Advantages[edit | edit source]

  • Accurate — follows the true solar year
  • Balanced – division of the year into equal parts
  • Dynamic — grouping of days into 3 × 3 is a powerful concept
  • Predictable — has a consistent, perennial structure
  • Simple — easy to learn and uncomplicated to use

It is structured, yet flexible enough to adapt to different uses and cultures:

  • Agriculture — follows natural cycles
  • Business — divided into equal parts, allows for flexible schedules
  • Civil — simple and predictable

The calendar is not tied to any culture/religion, except inevitably to that of the current scientific paradigm. While it is scientifically grounded, it does not oppose combination with cultural or religious concepts.

Disadvantages[edit | edit source]

  • Unfamiliarity — new divisions, units and beginning of year
  • No simple leap year rule — a tradeoff for astronomical accuracy over time
  • Yet another calendar — made by some commoner named Joakim (who is not the pope)

Variants[edit | edit source]

The foundation of this calendar enables several different implementations.

Traditional 12-month variant[edit | edit source]

This variant maintains the traditional 7-day week and 12 months, each month having 30 days. The months are perennial, but the weekdays are not.

Intercalary days belong to the seasons (named A-D) and the transition period (named X).

Months are offset from those of the Gregorian calendar, as new year is around March 20.

Season Month Days Gregorian
A 00
1 01 02 03 04 05 06 07 3 - 4
08 09 10 11 12 13 14
15 16 17 18 19 20 21
22 23 24 25 26 27 28
29 30
2 01 02 03 04 05 4 - 5
06 07 08 09 10 11 12
13 14 15 16 17 18 19
20 21 22 23 24 25 26
27 28 29 30
3 01 02 03 5 - 6
04 05 06 07 08 09 10
11 12 13 14 15 16 17
18 19 20 21 22 23 24
25 26 27 28 29 30
B 00
4 01 02 03 04 05 06 07 6 - 7
08 09 10 11 12 13 14
15 16 17 18 19 20 21
22 23 24 25 26 27 28
29 30
5 01 02 03 04 05 7 - 8
06 07 08 09 10 11 12
13 14 15 16 17 18 19
20 21 22 23 24 25 26
27 28 29 30
6 01 02 03 8 - 9
04 05 06 07 08 09 10
11 12 13 14 15 16 17
18 19 20 21 22 23 24
25 26 27 28 29 30
C 00
7 01 02 03 04 05 06 07 9 - 10
08 09 10 11 12 13 14
15 16 17 18 19 20 21
22 23 24 25 26 27 28
29 30
8 01 02 03 04 05 10 - 11
06 07 08 09 10 11 12
13 14 15 16 17 18 19
20 21 22 23 24 25 26
27 28 29 30
9 01 02 03 11 - 12
04 05 06 07 08 09 10
11 12 13 14 15 16 17
18 19 20 21 22 23 24
25 26 27 28 29 30
D 00
10 01 02 03 04 05 06 07 12 - 1
08 09 10 11 12 13 14
15 16 17 18 19 20 21
22 23 24 25 26 27 28
29 30
11 01 02 03 04 05 1 - 2
06 07 08 09 10 11 12
13 14 15 16 17 18 19
20 21 22 23 24 25 26
27 28 29 30
12 01 02 03 2 - 3
04 05 06 07 08 09 10
11 12 13 14 15 16 17
18 19 20 21 22 23 24
25 26 27 28 29 30
X 00
01

in leap years

·

·

Proposed 8-month variant[edit | edit source]

This variant has 8 octants of 45 days each, grouped into nonads of 9 days each.

Intercalary days belong to the seasons (named A-D) and the transition period (named X).

Season Octant Days
A 00
1st 01 02 03 04 05 06 07 08 09
10 11 12 13 14 15 16 17 18
19 20 21 22 23 24 25 26 27
28 29 30 31 32 33 34 35 36
37 38 39 40 41 42 43 44 45
2nd 01 02 03 04 05 06 07 08 09
10 11 12 13 14 15 16 17 18
19 20 21 22 23 24 25 26 27
28 29 30 31 32 33 34 35 36
37 38 39 40 41 42 43 44 45
B 00
3rd 01 02 03 04 05 06 07 08 09
10 11 12 13 14 15 16 17 18
19 20 21 22 23 24 25 26 27
28 29 30 31 32 33 34 35 36
37 38 39 40 41 42 43 44 45
4th 01 02 03 04 05 06 07 08 09
10 11 12 13 14 15 16 17 18
19 20 21 22 23 24 25 26 27
28 29 30 31 32 33 34 35 36
37 38 39 40 41 42 43 44 45
C 00
5th 01 02 03 04 05 06 07 08 09
10 11 12 13 14 15 16 17 18
19 20 21 22 23 24 25 26 27
28 29 30 31 32 33 34 35 36
37 38 39 40 41 42 43 44 45
6th 01 02 03 04 05 06 07 08 09
10 11 12 13 14 15 16 17 18
19 20 21 22 23 24 25 26 27
28 29 30 31 32 33 34 35 36
37 38 39 40 41 42 43 44 45
D 00
7th 01 02 03 04 05 06 07 08 09
10 11 12 13 14 15 16 17 18
19 20 21 22 23 24 25 26 27
28 29 30 31 32 33 34 35 36
37 38 39 40 41 42 43 44 45
8th 01 02 03 04 05 06 07 08 09
10 11 12 13 14 15 16 17 18
19 20 21 22 23 24 25 26 27
28 29 30 31 32 33 34 35 36
37 38 39 40 41 42 43 44 45
X 00 01

·

·

Zero-indexed variant[edit | edit source]

This variant is an even greater departure from traditional calendars. Although fairly simple, it is likely harder to grasp due to its unfamiliarity. Especially the concept of zero, which is here used to denote holidays at the start of a season.

A calendar year has 4 seasons, each having 10 sets (a grouping of days). Years, seasons, sets and holidays are zero-indexed, while nonads (9 days) and their workdays are one-indexed.

The days of the zeroth set of a season are holidays. The remaining 9 sets are ordinary nonads. That makes for a total of 36 nonads, or 324 workdays, per year. Using the concept of tridays, a person may work ⅔ of those (216 days per year), with 10-day seasonal holidays each quarter.

In this variant, the transition period is placed at the start of the year. Conceptually, it is between years, but every day must have a date. Here it belongs to the year it introduces, becoming the zeroth season.

Season Set Days
0 – Transition 0 0 1
1 – Spring 0 0 1 2 3 4 5 6 7 8 9
1 1 2 3 4 5 6 7 8 9
2 1 2 3 4 5 6 7 8 9
3 1 2 3 4 5 6 7 8 9
4 1 2 3 4 5 6 7 8 9
5 1 2 3 4 5 6 7 8 9
6 1 2 3 4 5 6 7 8 9
7 1 2 3 4 5 6 7 8 9
8 1 2 3 4 5 6 7 8 9
9 1 2 3 4 5 6 7 8 9
2 – Summer 0 0 1 2 3 4 5 6 7 8 9
1 1 2 3 4 5 6 7 8 9
2 1 2 3 4 5 6 7 8 9
3 1 2 3 4 5 6 7 8 9
4 1 2 3 4 5 6 7 8 9
5 1 2 3 4 5 6 7 8 9
6 1 2 3 4 5 6 7 8 9
7 1 2 3 4 5 6 7 8 9
8 1 2 3 4 5 6 7 8 9
9 1 2 3 4 5 6 7 8 9
3 – Autumn 0 0 1 2 3 4 5 6 7 8 9
1 1 2 3 4 5 6 7 8 9
2 1 2 3 4 5 6 7 8 9
3 1 2 3 4 5 6 7 8 9
4 1 2 3 4 5 6 7 8 9
5 1 2 3 4 5 6 7 8 9
6 1 2 3 4 5 6 7 8 9
7 1 2 3 4 5 6 7 8 9
8 1 2 3 4 5 6 7 8 9
9 1 2 3 4 5 6 7 8 9
4 – Winter 0 0 1 2 3 4 5 6 7 8 9
1 1 2 3 4 5 6 7 8 9
2 1 2 3 4 5 6 7 8 9
3 1 2 3 4 5 6 7 8 9
4 1 2 3 4 5 6 7 8 9
5 1 2 3 4 5 6 7 8 9
6 1 2 3 4 5 6 7 8 9
7 1 2 3 4 5 6 7 8 9
8 1 2 3 4 5 6 7 8 9
9 1 2 3 4 5 6 7 8 9

In these examples, seasons are named in English for the northern hemisphere. While the numbers are universal, the names will vary by hemisphere and language.

Dates are expressed using numbers and interpunct:

year · season · set · day

Season, set and day are single-digit. For example (2020-09-17 Gregorian):

2020·2·9·9

In the northern hemisphere, 2 · 9 · 9 tells you it's the 2nd season of the year, meaning summer. It is the last set (9) of that season, and therefore the last day (9) of summer. Autumn is upon us, and winter is coming. More dates:

2020·0·0·0 – Transition day

2020·0·0·1 – Leap day (2020 was a leap year)

2020·1·0·0 – New year's day, and the zeroth day of spring holidays

2020·1·0·1 – First day of spring holidays

2020·1·1·1 – First workday after spring holidays

2020·2·4·9 – Halfway point of the summer season (at noon)

2020·2·5·1 – The following day (there is no 2·5·0)

2020·4·9·9 – Last day of the year, and of the winter season

Any date with a zero in it is a holiday.

An interesting side effect is that the year can be rendered as a circle of 400 gradians, where the "skipped" zero-days function as separators between nonads.

In the 12-month and 8-month variants, a circle of 360 degrees can represent all calendar days.

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