Calendric Resources

Various links for beginners and advanced calendar-makers.
Y2K (year 2000 problem)
7-day week
Moon phases and related things
Easter (Christian festival)
Daylight Saving Time and time zones
Link Lists

best before 1999 :-)

Link lists are almost always too old, but you have to start somewhere when you're new to the field. I don't do maintenance of this page very often, so I hope that not many of these are stale when you read this. In arbitrary order, somewhat chunked ...

Introduction to Calendrics

The Calendar FAQ by Claus Tøndering gives basic astronomical facts, overviews of Christian, Hebrew, Islamic, French Revolutionary, Maya calendars and the week.(mirror site)

The Calendar Mailing List CALNDR-L. All who are seriously interested in calendars should subscribe. You can learn much from the very friendly people there.
To retrieve from the archives there send an email like this example for April 1998:

To:       listserv@ECUMAIL7.ECU.EDU
Subject:  CALNDR-L LOG APR98
Body:     Get CALNDR-L LOG9804
In October 1998, only archives from January 1997 and later were available.

Home Page for Calendar Reform by Rick McCarty (who also maintains CALNDR-L) descibes more than a dozen calendars, among them the ISO Week Date Calendar.

An article about ISO time and date formats by Markus Kuhn

Universal Time - timekeeping in decimal notation.

Today's Date and Time sports the current date in dozens of calendrical systems from various cultures - another lesson in calendrical relativity.

Online Calendar Conversions : Gregorian calendar, Julian calendar, day of week, Julian day number, Jewish calendar, French republican calendar.

At Lance Latham's Resource Management Systems look for SCDTL (Standard C Date/Time Library) and a link list "Other Good Date/Time Systems".

Articles on the Goddess lunar calendar (plus matching date conversion software) and other calendar studies (Gregorian, Orthodox, and Mayan Calendars, astronomical considerations and more) by Peter Meyer

Toke Nørby's Perpetual Calendar gives the introduction dates of the Gregorian calendar; especially relevant for postal history (stamps). Long link list and email addresses of calendar experts. Explains the French Republican calendar.

William Morris' nice main calendar page (requires Java) gives Moon pictures for both hemispheres, date in Lunar Tree Calendar, Chinese Lunar, Gregorian, Julian, Jewish, Islamic, Hindu Amanta System, Hindu Purnimanta System, French Revolutionary.

Java Calendar Conversions by Mark E. Shoulson (13 different calendars 1999-04-09 and counting ...)

Scott Lee's Calendar Conversions

Douglas Zongker's Calendar Conversions

Calendars and their History - many parts of the oft-referenced treatise by L. E. Doggett. An effort by Lyle Huber. In November 1998, it contained the sections 1(Introduction), 2(Gregorian), 3(Hebrew), 4(Islamic), 5(Indian), 6(Chinese), 8(Julian), 10 (References, to be added later). Detailed explanations.

Mesoamerican Prehispanic Calendars (Maya, Nahua).

Felix Verbelen gives info on ancient astronomical phenomena: Solar Eclipses on Earth - Catalogue of all Solar eclipses visible on Earth from 1001 BC to AD 2500, Mesoamerican Solar eclipses - Catalogue of Solar eclipses visible in Mesoamerica from AD 800 to AD 1600, Lunar Eclipses on Earth - Catalogue of all Lunar eclipses visible on Earth from 1001 BC to AD 2500, Venus - Heliacal risings and settings visible from Yucatan AD 800 to AD 1600, Delta T - Delta T = TT - UT, Times are given UT.

Current date in the Baha'i calendar (19 months of 19 days plus four or five intercalary days). Sie wußten vermutlich, daß der Meton-Zyklus 19 Jahre dauert.

Indonesian time keeping systems (Gregorian, Islamic and Javanese 8-year cycle with 3 leap years).

Balinese calendar

Solar days are of different length, depending on the time of the year. Sundials are up to 14 minutes fast (in February) and up to 16 minutes slow (in November) due to the orbit of the Earth around the Sun. The Equation of Time explains this. Excerpt: "On January 2, the Earth is 1.7% closer to the Sun than average and thus the angular velocity is 3.4% larger (conservation of angular momentum). This makes the solar day longer than the sidereal day by about 8sec more than average ..."

A Bioregional Calendar (ABC), based on equinoxes with four-day "week". Counts years "after Hiroshima" (A.H.) with 16 multilingual named months of 22-23 days.

ERROR in GRO #48 intensely points to some inaccuracies in current astronomical texts concerning the vernal equinox (VE) and lengths changes of the various VE year definitions over time (with graph). This page is important to read for advanced calendar-makers, notwithstanding its indignant tone.

Connotations, rhymes and lore on various calendric periods

The Runic Half-Month Calendar (maybe not true to tradtion, but worth a look for the connotations - the stuff ritual or magic calendars are made of).

History of Astronomy: Calendars, Time and Chronology Candace Mcbride's neo-pagan calendars (at bottom of page)


The Millennium Clock - an inspiration to think about clocks and the long future.

The Year 2000 (Y2K) problem - a link list by an early warner.

Y2K links from the large link collection Calendar Zone (see above).

Current bet on a deadly Y2K disaster.

Another antidote to Millennial craze or acute calendritis Toward A Nonarbitrary Calendar (Or Not) which refers to
Pope Icky's "just say no to round numbers"alphabetical calendar (a base-26 year count, starting in the year A = 585 B.C., the year with the supposedly earliest event we can date exactly, so CUI = 1998, ... , CUP = 2005 etc)

The Seven-Day Week

An article about the history and various (some quite esoteric) connotations of the Seven-Day Week

From week and year, construct a whole self-similar calendar for space dwellers, the Seven Space calendar

Origin of the Seven-Day Week from Claus Tondering's Calendar FAQ

History of the week (from the calendar FAQ elsewhere - older version)

Remarks on Seven-Day Week Origin

The special marked days in the Babylonian month (lunar week scheme) and the origin of (western) weekday names

Isaac Asimov tells a story how the week emerged from Babylonian moon worship (circa 600 BC).

Convert calendar date to day of the week

"Doomsday method" of calculating the day of the week.

Karl Palmen's playing card calendar (plus links to similar week-based calendars)

Names of the weekdays in thirty languages at Seven-Day Week by Vincent Mallette

Bill Hollon's in-depths treatise on week-origins, planetary hours, names and number of days in the week
(see also his Fixed-Week Calendar which would repeatedly break the weekday cycle.)

More weekday connotations at The Times of Our Lives: Social Rhythms and Cycles

Other notable weekday connotations

making fun of the week:
rearrange the weekdays
8-day week, 15-month year
half of 10-day week is weekend


Meyer-Palmen Solilunar Calendar - more accurate than old Gregory plus alignment with eclipses! (Anagramatically known as "supernormally Melanie" ;-)

Compute the approximate times of the four phases of the Moon for any year from 1 to 2246 CE (program code is available, too!).
In case the above site is not available, look at moon phases from 1923 to 2105 CE (lunation #0 to #2262) at this site (185 kB).

Rather complete information about moon phases near today (current lunation). Gives different times than the above approximation (about a minute off) for the lunar phases.

The U.S. Naval Observatory's table Phases of the Moon 1990-2005 makes it easy to spot months with more than four moon phases (e.g. there are two full moons in July 2004). Probably one of the most exact moon phase data sets on the net.

Tidal calculations

Special days in the (lunar) Taoist calendar

Moon calendar for months near the current month. Gives zodiacal sign for each day (probably Austria-centered). Auch in Deutsch: Mondphasen-Kalender mit astrologischen Tierkreiszeichen.

The Lunar Calendar of the Easter Island (Tablet Mamari).

Of the ten greatest panics on the stock market (1929-1997), eight occurred two days before an October new moon.


Compute the date of Gregorian & Julian Easter (also Mayan calendrics).

Compute the Easter date between 1700 and 2199 with a little perl program

More about Christian Easter algorithms and traditions (Anglican, Catholic, Orthodox, Protestant).

Compute the Easter date with Conway's elaborate formulae.

Ostern, Hasen, Ostara - Wissenswertes zum alten Frühlingsfest (christliches Fest seit 325 CE)

Daylight Saving Time (DST)

Dual Sun Time - beyond DST

Daylight saving time did not save electricity in Germany:
Sommerzeit endet am 25. Oktober 1998, Pressemeldung von

PTB: Zeitzonen time zones of the world - by Physikalisch-Technische Bundesanstalt. PTB is the German organization for measurement standards. Location of the German atomic clocks.

If you want accurate, up-to-date, and globally comprehensive time-zone (including "daylight-saving") information, get
You might be surprised just how comprehensive it is! It is human readable, but not very easily; get for C code that uses it.

Link Lists

These may be helpful when searching a specific theme in-depth.

At the large link collection Calendar Zone you can submit your own calendar page to one or more of the many categories. It is then automatically included in the category you select. You can even suggest new categories.

Justin White's CalendarHome gives: Interactive | The Year 2000 | Chinese | Mayan | Cultural | Holidays and Celebrations | Historical | Astronomical | Real World Calendars | Calendar Reform | Software | General Calendar Information | Genealogy Links | More Link Sites | Submit Calendar URL

Calendrics at this site

Essays on mathematical themes

© Copyright 1998, Mario Hilgemeier, email: contact
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