28x Time Standard

Draft v0.1

Status: Draft (public)

Canonical Home: 28x.org

Scope: Calendar structure, epoch, date format, and normative rules for representation

1. Purpose

The 28x Time Standard defines a regular, lunar-inspired calendar system intended for clarity, predictability, and long-horizon coordination across human and computational systems.

The standard provides:

  • A uniform calendar lattice (13 × 28 days)
  • Intercalary days to maintain seasonal alignment
  • A fixed epoch for absolute date representation
  • A stable, machine-readable date format
  • A basis for deterministic mapping between Gregorian and 28x dates

28x is designed to coexist with the Gregorian calendar. It does not require cultural replacement to be useful.

2. Terms and Definitions

28x Year: A year consisting of 13 moons of 28 days each, plus Intercalary Days.

Moon: A fixed-length month-like unit of 28 consecutive days.

Week: A 7-day subdivision of a moon.

Intercalary Day (ID): A single day outside the moon/week lattice used to complete a standard year.

Leap Intercalary Day (LID): An additional day outside the moon/week lattice used in leap years to maintain seasonal alignment.

Day Out of Time (DOOT): A cultural alias for the Intercalary Day (non-normative).

Epoch: The reference point from which all 28x dates are computed.

Corresponding Gregorian Year: The Gregorian year in which 28X-YYYY-01-01 occurs.

3. Calendar Structure

Each 28x year consists of:

  • 13 moons
  • 28 days per moon
  • 7-day weeks
  • 364 structured days
  • 1 Intercalary Day (ID)

Standard year: 365 days (364 structured + 1 ID)

Leap year: 366 days (364 structured + 1 ID + 1 LID)

3.1 Regularity properties

  • All moons are identical in length.
  • The internal lattice is stable: moon boundaries and weekdays do not drift within the 28x system.
  • Leap-year mechanism maintains seasonal alignment (see §4).

4. Epoch

4.1 Epoch statement (normative)

Gregorian 2026-03-20 (UTC civil date) = 28X-0000-01-01

Year 0000 is the first 28x year.

This epoch SHALL be treated as fixed and SHALL NOT be altered in future versions of the standard.

4.2 Meaning of the epoch

The epoch establishes a stable, absolute coordinate system for dates. Once the epoch is fixed, any date—past or future—may be expressed in 28x coordinates via deterministic computation.

4.3 Leap-Year Rule (normative)

A 28x year is a leap year if its corresponding Gregorian year is a Gregorian leap year.

A Gregorian year is a leap year if it is:

  • divisible by 4
  • except if divisible by 100
  • except if divisible by 400

The corresponding Gregorian year is the Gregorian year in which 28X-YYYY-01-01 occurs.

5. Intercalary Days

5.1 Placement (normative)

Intercalary Days occur after:

  • Moon 13, Day 28

and before:

  • Moon 1, Day 1 of the following year.

In a standard year, only the Intercalary Day (ID) occurs.

In a leap year, the Intercalary Day (ID) is followed immediately by the Leap Intercalary Day (LID).

Intercalary Days are not assigned to any moon or week and have no weekday.

5.2 Naming (normative and non-normative)

Canonical names: Intercalary Day (ID), Leap Intercalary Day (LID) (normative)

Cultural alias: Day Out of Time (DOOT) for Intercalary Day (non-normative)

Implementations MAY display the cultural alias, but MUST preserve the canonical meaning and computational handling.

6. Date Representation

6.1 Canonical date format (normative)

Structured days SHALL be represented as:

28X-YYYY-MM-DD

Where:

  • YYYY is a signed integer year in zero-padded form (see §6.4)
  • MM is the moon number 01–13
  • DD is the day number 01–28

Example:

28X-0000-03-14

6.2 Intercalary Day representation (normative)

Intercalary Days SHALL be represented as:

28X-YYYY-ID (Intercalary Day)

28X-YYYY-LID (Leap Intercalary Day, leap years only)

Examples:

  • 28X-0000-ID (Intercalary Day in Year 0000)
  • 28X-0004-LID (Leap Intercalary Day in Year 0004, a leap year)

Implementations MUST treat ID and LID as outside the moon/week lattice.

LID occurs only in leap years and immediately follows ID.

6.3 Validation rules (normative)

  • MM MUST be between 01 and 13 inclusive.
  • DD MUST be between 01 and 28 inclusive.
  • 28X-YYYY-ID MUST NOT include MM or DD.
  • 28X-YYYY-LID MUST NOT include MM or DD.
  • Intercalary Day (ID) MUST occur exactly once per 28x year.
  • Leap Intercalary Day (LID) MUST occur exactly once per leap year and MUST NOT occur in non-leap years.

6.4 Year numbering and backdating (normative)

28x supports representation of dates before the epoch.

Year numbering begins with Year 0000 at the epoch.

Years prior to Year 0000 SHALL be represented using a leading minus sign.

Examples:

  • 28X-0000-01-01 (epoch date)
  • 28X--0001-13-28 (one year before epoch)

(Exact formatting for negative years MAY follow ISO-8601 conventions; implementations SHOULD document their formatting choice consistently.)

7. Mapping to Gregorian Dates

28x is an epoch-based calendar. Given the epoch, mapping between Gregorian dates and 28x dates is computed by counting whole days forward or backward.

7.1 Determinism (normative)

Given a specific Gregorian date and a fixed epoch, conversion results MUST be deterministic.

7.2 Reversibility (normative)

Implementations SHOULD ensure conversions are reversible such that:

Gregorian → 28x → Gregorian returns the original day (date) value, assuming consistent day-boundary conventions.

7.3 Algorithm status (non-normative)

This version defines the calendar structure, epoch, and date formats. A fully specified reference conversion algorithm and test vectors are planned for a subsequent version.

8. Retrospective Mapping

Dates prior to the epoch may be expressed in 28x coordinates using negative year values and the same structural rules.

Such mappings are mathematical coordinate assignments and do not imply historical usage of the 28x calendar.

9. Cultural Observances (Non-normative)

The following observances MAY be associated with 28x cultural practice. They are outside the canonical computation rules.

9.1 Day Out of Time (DOOT)

DOOT is a cultural name for the Intercalary Day.

9.2 Tau Day

Tau Day MAY be observed on Moon 6, Day 28 (28X-YYYY-06-28). This observance is purely symbolic and non-normative.

Properties (non-normative):

  • Occurs on the 168th day of the structured calendar (6 × 28 = 168)
  • Provides a convenient symbolic moment for reflection or recalibration
  • Not mathematically tied to the midpoint of the 28x year lattice

Tau Day is excluded from 28x date computation and does not affect conversions or the canonical calendar structure.

10. Versioning and Stability

10.1 Versioning model

The standard uses semantic versioning:

  • MAJOR: backward-incompatible changes (expected to be rare)
  • MINOR: additive features that preserve compatibility
  • PATCH: clarifications and error corrections

10.2 Stability commitments (normative intent)

Future versions SHALL preserve:

  • The epoch definition
  • The 13 × 28 lattice
  • The Intercalary Day concept and leap-year mechanism
  • Backward compatibility for date representations

11. Governance (Summary)

28x is stewarded as an open standard with conservative evolution. Governance details, proposal process, and stewardship roles are described on the Governance page.

Notes for Implementers (Non-normative)

28x is intended to be:

  • easy to represent
  • easy to validate
  • easy to compute against once the conversion algorithm is implemented
  • stable across decades
  • seasonally aligned through the leap-year mechanism