"The Calendarium Solaris is offered for voluntary adoption worldwide. It is designed to operate alongside any existing calendar system and carries no religious, political, or hemispheric associations."
What is the Calendarium Solaris?
The Calendarium Solaris is a universal solar calendar, precisely synchronised with the tropical year, the time it takes Earth to complete one full orbit around the Sun. Unlike the Gregorian calendar, which is rooted in historical convention, the Calendarium Solaris is anchored to an observable astronomical event: Equinox 0°, the moment when solar longitude reaches exactly 0°.
Every year begins on this exact equinox, a moment that occurs simultaneously across the entire planet, making the Calendarium Solaris a truly universal, hemisphere-neutral timekeeping system. The official start is Equinox 0°, Year 0 (20 March 2028 UTC). A trial period runs from Equinox 0° 2026 alongside existing calendars. During this trial period, each Calendarium Solaris date is displayed alongside the corresponding Gregorian date. After Intercalary Day, Year 4, the calendar stands independently.
Perfect Structure
12 months of exactly 30 days each. Every month contains exactly 6 weeks, always starting on Solcycli and ending on Paxcycli.
Balanced Quarters
Four perfectly equal quarters of 91 days each, 90 weekdays (18 weeks) plus one floating Anchor Day marking an equinox or solstice.
Astronomically Anchored
The year always begins at Equinox 0°, a universal, observable astronomical event, separated from arbitrary cultural conventions.
Highly Accurate
With a four-rule intercalation system, the Calendarium Solaris stays aligned with the tropical year for approximately 16,000 years.
The Five-Day Week & Outside Days
The conventional seven-day week is an ancient historical construct that forces months and years out of alignment. The Calendarium Solaris introduces a highly efficient, permanently stable 5-day week. Because every month has exactly 30 days, each month contains exactly 6 weeks. The days of the week never shift, every month always begins on Solcycli and ends on Paxcycli.
Solcycli
Initiation, the rise
Start of the week
Luxcycli
Growth, the light
Building momentum
Maxcycli
Apex, the peak
Height of the week
Descycli
Descent, winding down
Transition day
Paxcycli
Rest and peace
End of the week
Outside Days
The days that fall outside the 360-day month structure are called Outside Days. Four of these are Anchor Days, each marking one of the four astronomical equinoxes or solstices; one Yearday closes the solar year; and in leap years an Intercalary Day follows. These days carry no weekday designation, they pause the week cycle without ever disrupting it. They serve as moments of global pause, marking the great turning points of Earth's orbit.
Year Structure
The year consists of 12 months of 30 days, following a permanent 5-day week cycle (Solcycli, Paxcycli). Four Anchor Days mark the precise equinoxes and solstices; a Yearday closes the cycle. In leap years, an Intercalary Day is appended. All outside days carry no weekday designation.
| # | Month / Anchor | Days | Position |
|---|---|---|---|
| — | Equinox 0° | 1 | Day 1, Equinox 0°, start of year |
| 1 | Primisol | 30 | |
| 2 | Secundisol | 30 | |
| 3 | Tertisol | 30 | |
| — | Solstice 90° | 1 | Day 92, Solstice 90° |
| 4 | Quartisol | 30 | |
| 5 | Quintisol | 30 | |
| 6 | Sextisol | 30 | |
| — | Equinox 180° | 1 | Day 186, anchor day between Septisol 3 & 4 |
| 7 | Septisol | 30 | |
| 8 | Octisol | 30 | |
| 9 | Nonisol | 30 | |
| — | Solstice 270° | 1 | Day 275, anchor day between Decisol 1 & 2 |
| 10 | Decisol | 30 | |
| 11 | Undecisol | 30 | |
| 12 | Duodecisol | 30 | |
| — | Yearday | 1 | Closes the year |
| — | Intercalary Day | 1 | Closes the leap year according to the intercalation rules |
Intercalation Rules
Because the tropical year is not exactly 365 days, the Calendarium Solaris uses a four-rule intercalation system. This produces an average year length of 365.24225 days, just a few seconds off from the tropical year, ensuring alignment for approximately 16,667 years.
Rule 1, Divisible by 4
Intercalary Day added.
Rule 2, Divisible by 100
No Intercalary Day.
Rule 3, Divisible by 400
Intercalary Day added.
Rule 4, Divisible by 4000
No Intercalary Day.
How Does It Compare?
The Calendarium Solaris is approximately 5 times more accurate than the Gregorian calendar in long-term synchronisation with the tropical year.
| Calendar | Avg. Year Length | Deviation | One-day drift after |
|---|---|---|---|
| Julian | 365.25000 days | +0.00781 days/year | ≈ 128 years |
| Gregorian | 365.24250 days | +0.00031 days/year | ≈ 3,226 years |
| Khayyam | 365.24242 days | +0.00023 days/year | ≈ 4,348 years |
| Calendarium Solaris | 365.24225 days | +0.00006 days/year | ≈ 16,667 years |
Experience the Calendar
See today's Calendarium Solaris date, explore months and years, and add your own appointments, exportable to any calendar app.
Open the Calendar ☀