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 x 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 Holocene Era, year zero being 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, mathematician, philosopher and poet Omar Khayyam's 11th century reform of the Jalali calendar.
For more details, see Definition and Questions and Answers.
- Accurate — follows the true solar year
- Balanced – division of the year into equal parts
- Dynamic — allows for different variants and uses
- 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.
- 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)
Observation-based calendars embrace the non-uniform motion of the Earth around the Sun, as well as any short-term perturbations. The future can never be predicted with absolute certainty, due to the dynamic nature of the universe. The only way to know with absolute certainty the length of the year is through observation.
Calendars based on the Jalali calendar, like this one, are the most accurate in relation to the true solar year. Today's astronomical knowledge and computing power enable us to predict with very high precision the instant of the northward equinox. Even still, observational measurements are necessary to check the correspondence between the mathematical model and reality. The exact instant can now be measured to an accuracy of better than 1 millisecond (Heydari-Malayeri, 2004).
However, as Heydari-Malayeri writes,
The precise knowledge of the year duration is one thing, using it practically to construct a calendar system is another, because the calendar year of 365 entire days is not equal to the real solar year. A good calendar is therefore the one whose intercalation system yields a year length the nearest possible to the reality.
My aim has been to achieve this in a simple and useful way.
- Reform an existing calendar
- Follow the traditional 7-day week
- Incorporate the lunar phases, as lunisolar calendars are inherently complex and irregular
- Accurately follow the astronomical seasons, as their lengths change over time
- Align with the zodiac, due to the (lunisolar) precession of the ecliptic
However, features like these may be applied, just as they are applied to existing calendars. For example, the unbroken chain of 7-day weeks may be used just like in the Gregorian calendar, with weekdays retaining their traditional names and cultural/religious significance, if so is desired.
- A concise review of the Iranian calendar (Heydari-Malayeri, 2004)
- Calendar Reform (McCarty)
- Calendars New and Old (Meyer)
- The Non-implemented 33-Year English Protestant Calendar (Steel, 1999)
- How Britain got the Calendar Wrong (Steel, 1999)
- One Day Too Many (Schlag)
Doesn't mention the Persian calendar. This calendar would also solve all the faults of the Gregorian calendar. - The Persian calendar for 3000 years (Borkowski, 1996)