Chronology Lab

Calendar types & rhythms

Compare solar, lunar, lunisolar, and civic calendars so you can plan across traditions.

Type comparisons

Modes

Gregorian (solar)

The modern international calendar tracks Earth’s orbit with 365-day years plus leap days, boundary months, and the familiar weekdays.

  • 365 days, leap day in years divisible by 4 except short centuries.
  • Used for civil, financial, and scientific schedules globally.
  • Anchors the ISO week system and common fiscal quarters.

Lunar (Islamic)

Twelve lunar months define the Islamic calendar, drifting through the solar year over a 33-year cycle.

  • Each month starts with the new moon; years are ~354 days.
  • Moves across seasons, so Ramadan can fall in any quarter.

Lunisolar (Hebrew, Chinese)

These calendars add leap months when needed to keep lunar months aligned with solar seasons.

  • Uses Metonic cycles to insert leap months roughly every 2–3 years.
  • Preserves festival seasons like Passover and Lunar New Year.

Fiscal & astronomical

Organizations often adopt bespoke calendars—fiscal years, celestial seasons, or ISO weeks.

  • ISO weeks start Monday and keep 52-week consistency.
  • Scientific programs track equinoxes/solstices for observation scheduling.

Context & decisions

Guidance

When planning, pick the calendar that matches your audience. Use the Gregorian for civil deadlines, lunar for cultural observances, and lunisolar for celebrations that must stay tethered to a season.

Strategy: Document which calendar you refer to in project briefs, especially when working across regions that follow differing cycles.
Solar Lunar Lunisolar Fiscal