Serendipity: Calendar Studies

Calendar Studies

Last modified: 1996-10-26 G (2996-25-15 GLC)

Gregorian and Julian Calendars The Goddess Lunar Calendar

The Maya Calendar Other Lunar Calendars

Other Calendrical and Astronomical Material

Gregorian and Julian Calendars

"Due to an arcane glitch, most of the world's computers will reset themselves to 1900 when the year 2000 rolls around. The problem seems harmless enough, but the results could be devastating: Social Security and Medicare payments might grind to a halt, satellites could go cross-eyed, and long-distance telephone connections could get snarled. The cost for fixing the problem worldwide may be $600 billion, with the United States footing 10 to 40 percent of the bill." -- Philadelphia Inquirer
It has been estimated that as a result of this "millennium bug" perhaps 10% of firms around the world will go bankrupt because of the failure either of their own computer systems or of those of their essential suppliers. More in Nicholas Moss: "Europe's date with disaster"
Peter Meyer: "The Julian and the Gregorian Calendars"
An article explaining the origin of the present European calendar and its reform by Pope Gregory XIII in 1582.
Peter Meyer: "The ISO Date Format"
A note concerning date formats, especially the ISO date format.
Peter Meyer: "Julian Day Numbers"
A note on the Julian day numbering system.
Peter Meyer: "Date Conversion Functions in C"
This article will be of interest mainly to C programmers, but if you have ever wondered whether there can be a year with no (or three or more) Friday the 13ths then the answer is here. An earlier version of this article appeared in the March 1993 issue of Dr Dobbs Journal.
CALCONV.EXE
A useful little calendrical tool (it is DOS software; you can download it - it's about 8K) that uses the functions presented in the above article. I wrote this some years ago.

The Goddess Lunar Calendar

Peter Meyer: The Goddess Lunar Calendar
A 25-month calendar whose months stay in sync with the lunar cycles (on average) and are named after goddesses from fourteen different cultures.
German translation by Klaus Scharff: Der Kalender der Göttinnen
MS-DOS software for conversion between dates in the Goddess calendar and dates in the Gregorian calendar:
- Executable program: GLC.EXE
- German version: LKG.EXE
- Source code and executable: GLC.ZIP
Peter Meyer: The Accuracy of the Goddess Lunar Calendar
Just how accurate is the Goddess Lunar Calendar?
German translation by Klaus Scharff: Die Genauigkeit des Lunarkalenders der Göttinnen
Simon Cassidy: Comment on Future Accuracy
Concerning the infeasibility of predicting the accuracy of calendars for more than a few millenia.
Peter Meyer: The Lunar Calendar in The Invisible Landscape
German translation by Klaus Scharff: Der Lunarkalender in The Invisible Landscape

Other Lunar Calendars

Steve Renshaw and Saori Ihara: The Lunar Calendar in Japan
With links to: Lunar Calendars, Solar Terms, Names for Months, The Solar System and Names for Days, Calendar Reform in Japan and Matasaburou's Calendar
The Lunar phase Calendar, 1416-1417 A.H (1995/96/97)
The Islamic calendar. With links to "The history of the Hijri calendar" and "The Specification and method of calculating the Hijri calendar".
Start of the Chinese Lunar Calendar
The alleged beginning of the Chinese calendar at a planetary conjunction on March 5, 1953 B.C. (-1952-03-05).
Jacques Guy: The Lunar Calendar of Tablet Mamari

"My opinion is that it is not a calendar, but an astronomical canon for predicting when to insert intercalary nights by observing the apparent diameter of the moon. Polynesian priests used to have competitions as to who would correctly predict astronomical events (eclipses, the rising of some constellations, moon phases, etc.). But those lines have been called a 'calendar' ever since Barthel identified them as such almost 40 years ago now."
Moon facts.
Facts about the moon now.

The Maya Calendar

Maya and Goddess Calendars (documentation)
In 1990 I developed and published a program called Mayan Calendrics to convert between Maya and European dates. In 1994 I added Goddess Lunar Calendar conversions (now updated to the 1996 version) and in 1996 I added the ability to derive a list of possible correlation numbers from the association of a tzolkin/haab date with a particular European date. Here is the documentation which accompanies the software (for which see below).
Maya Kalender und Kalender der Göttinnen (Dokumentation)
A German translation by Klaus Scharff.
Maya and Goddess Calendars V5.10 (DOS software)
Clicking on this link will initiate the download of a file called MGC.EXE. This program converts both dates in the Maya Calendar and dates in the Goddess Lunar Calendar (see above). The program creates four textfiles the first time the Help is accessed. See above for the documentation.
Maya Kalender und Kalender der Göttinnen (Software)
The German version of the software (text translated by Klaus Scharff).
Links to other documents on the web concerning the Maya Calendar and links to pages of links to Maya-related web sites.

Other Calendrical and Astronomical Material

Grolier's article on "Calendars"
Information leaflets from the Royal Greenwich Observatory
Royal Greenwich Observatory Information Leaflet No. 48: Leap Years
L. E. Doggett: Calendars
From the Explanatory Supplement to the Astronomical Almanac. This contains much information on the Julian and the Gregorian calendars as well as on several non-European calendars such as the Chinese.

"Leap Years" and "Calendars" propagate a basic error concerning the tropical year. This is explained in the following two documents:

Simon Cassidy: Error in Statement of Tropical Year
Simon Cassidy: The Tropical and the Anomalistic Year

CalendarLand
Numerous links to calendar-related web sites.
Definitions of time from the U. S. Naval Observatory.
Social Rhythms, Cycles and Clocks

"One basis of social life is the predictability of others' actions. One way that this is obtained is through the social creation of regulated rhythms and temporal boundaries for specific social activities."
The date of Easter.
Several Usenet articles about its determination.
One World Global Calendar
Important dates in calendars from different cultures.
Genealogy, Calendars and Dating
The First Sunrise in the New Millennium
The Positivist Calendar of Auguste Comte
The World Calendar
A calendar with several advantages but one flaw: It requires interruptions in the 7-day cycle of the week, a cycle which has probably remained unbroken for several thousand years.
The Cotsworth Calendar
Today's date in each of the above calendars can be found at Today's Calendar and Clock Page, along with links to further calendrical web pages.
William Becker: Two Perpetual Calendars
Both a 12-month and a 13-month perpetual calendar.
The Erisian (or Discordian) Calendar
Hail Eris, Mother of Discord!
The Simtel.Net MS-DOS Collection includes some calendrical and astronomical software.
A Calendar Mailing List: CALNDR-L
The list maintainer, Rick McCarty, writes:

"CALNDR-L is an unmoderated email forum for discussion of social, historical and philosophical dimensions of Calendars and Time Reckoning."
Four letters sent to this mailing list:
- Simon Cassidy: Re 4-1/8 yr. Leap Rule responses of Richard, Jim and Amos
- Simon Cassidy: Implementing a correct 33-year calendar reform
- Chris Carrier: How long is a year -- EXACTLY?
- Simon Cassidy: Re: How long is a year -- EXACTLY?

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Gregorian and Julian Calendars	The Goddess Lunar Calendar
The Maya Calendar	Other Lunar Calendars
Other Calendrical and Astronomical Material