Calendar Studies
Hermetic Systems

"Once pursued for its own sake, [astronomical observation] comes to provide the vehicle for scheduling rituals and coordinating the activities of complex society. With the help of the stars, the year and its divisions exist as instruments of organizational authority. The formation of a calendar is basic to the formation of a civilization. The calendar was the first symbolic artifact that regulated social behavior by keeping track of time."
— John Zerzan: Time and Its Discontents


The Julian and
Gregorian Calendars
1. The Julian Calendar
2. The Gregorian Reform
3. Adoption of the Gregorian Calendar
4. Astronomical Year Numbering
5. The Proleptic Julian and Gregorian Calendars
6. Variation in the Tropical Year
7. Accuracy of the Gregorian and Orthodox Calendars
8. True Length of the Tropical Year
Star Award
Astronomical Year Numbering and the Common Era Calendar
The ISO Date Format A note concerning date formats, especially the ISO date format.
Types of Calendar Lunar, solar, lunisolar, solar-count, etc.
Julian Day Numbers The nature and origin of the Julian day number system.
Chronological Julian Date An explanation of this concept with examples of use.
The Dee-Cecil Calendar and its Date Conversion Algorithms A description of the Dee and Dee-Cecil Calendars, plus algorithms for conversion of dates in these calendars to and from Julian day numbers.
John Dee's Calendar and God's Longitude John Dee's secret plan for the implementation of his new 33-year-cycle calendar
Lunar Calendars The synodic month and how it is changing.
The Hermetic Leap Week Calendar A calendar with an integral number of 7-day weeks in each year, and which stays in sync with the seasonal year.
The Hermetic Lunar Week Calendar A solilunar calendar which avoids the problem of rescheduling with each new year.
The Archetypes Calendar An accurate lunar calendar with (mostly) weeks of 10 days.
Why Seven Days in a Week? Why not six or eight?
The Maya Calendar Article about the Maya Calendar
See also the documentation for the Mayan Calendrics software
The Structure of the Chinese Calendar How the Chinese Calendar depends on the times of astronomical events.
The Liberalia
Triday Calendar
A new calendar combining a lunar calendar and a solar calendar with 3-day cycles in common.
The Meyer-Palmen
Solilunar Calendar
A calendar consisting of 60-year cycles which stays in sync both with the Moon and with the seasons.
The Goddess Calendar A calendar whose 13 months accord with the lunar cycles and are named after thirteen goddesses.
The Tabot Calendar A calendar with (mostly) 30-day months in which New Years Day always falls on November 2nd in the Gregorian Calendar.
Two Integral-Week
Solar Calendars
Two new solar calendars in which years have an integral number of weeks.
When Did the New
Millennium Begin?
It depends on which system you use for numbering years.
German translation:
Wann beginnt das neue Jahrtausend?
Portuguese translation:
Quando É Que o Novo Milénio Começará?
Interconverting Tibetan and Western Years  
Interconverting Chinese and Western Years
The Gregorian Calendar is a Religious Calendar


Writings by Others: Lance Latham:
Simon Cassidy:
Karl Palmen:
Duncan Steel:
Robert Poole:
Kirkpatrick Sale:
Jean Meeus:
John R. Beattie:
Bohumil Böhm and Vladimir Böhm:
William Becker:
Paul Hill:
W. M. Flinders Petrie:


Calendrical and Astronomical Links

Maya Calendar Links

Date/Calendar Software Hermetic Systems Home Page