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Definition

  • A perennial solar calendar for Earth based on astronomical observations
  • The calendar year begins at the northward equinox measured from the prime meridian
  • 360 calendar days + 5 or 6 intercalary days
    • 4 quarters of 90 calendar days + 1 intercalary day
    • 8 months of 45 calendar days
    • 40 weeks of 9 calendar days
      • 3 × 3 days
    • 1 or 2 intercalary transition days at the end of the year
  • Proposed epoch is the beginning of the human era (10001 BC)

New Year

The calendar year begins at the midnight closest to the instant of the northward equinox 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 instant should be based on calculations for the prime meridian 1
    • Local new year may be calculated from this instant using a time offset
    • The local new year should be celebrated, not that of the prime meridian 2
    • It may also be observed locally, even with a sundial
  • Inherits the 33-year intercalation cycle from the Persian calendar (Heydari-Malayeri, 2004)
    • Calculations should use the true northward equinox year, not to be confused with the mean tropical year 3

Units

  • year: 360 calendar days + 5 (or 6) intercalary days
  • quarter: 1/4 of a year's 360 calendar days + 1 intercalary day
  • octant: 1/8 of a year's 360 calendar days
  • nonad: 9 calendar days
  • triad: 3 calendar days
  • day: 1 nychthemeron
  • transition: a period of 1 (or 2) intercalary days

The names "octant", "nonad", "triad" and "transition" are descriptive only, better names may be chosen.

Structure

  • The year has 360 calendar days and 5 (common year) or 6 (leap year) intercalary days
  • The year is divided into 4 equal quarters, each having 91 days
    • 1 intercalary day that represents the equinox/solstice
    • 90 calendar days
  • The year's 360 calendar days may be divided as follows
    • Proposed division: 8 octants ("months") and 40 nonads ("weeks")
      • 8 octants of 45 calendar days (2 octants per quarter)
      • 40 nonads of 9 calendar days (10 nonads per quarter, 5 nonads per octant)
        • Each nonad may be further divided into 3 triads of 3 calendar days
    • Traditional division: 12 months
      • 12 months of 30 calendar days (3 months per quarter)
      • Drawback: A month can not fit a whole number of nonads (3.3 nonads per month)
  • The remaining 1 or 2 days at the end of the year are intercalary transition days before the new year

Proposed epoch

The midnight closest to the northward equinox of the Human Era epoch of the Holocene Calendar, 10001 BC, maintaining a reference to the currently dominant Anno Domini (12020 HE = 2020 AD).

Proposed notation

  • The formatting of dates should be universal
  • The numbering of units must be universal
    • Divisions of the year are 1-indexed (namely octants/months, nonads and quarters)
    • Days of the transition period and quarters are 0-indexed
      • Day 0 of a quarter is the quarter's intercalary day
    • Days of other divisions of the year are 1-indexed (namely octants/months, nonads and fiscal quarters)
  • The naming of units may vary by language, locale or culture

The quarters could be named A-D, as in Asimov's World Season Calendar, and X for the transition period (for example A-0, B-0, C-0, D-0, and X-0).

Notes:

  1. Instead of Tehran, this calendar's point of reference effectively becomes 0°N 0°E at sea level
  2. Could be the exact local instant of the northward equinox or local midnight as calculated from the prime meridian
  3. A widespread misunderstanding that must be avoided when implementing this calendar