Wilson's Almanac on how we date things

Related terms: Calendar, Aztec, Hebrew, Islamic, moveable feast, 
moveable feasts, fast, movable, lunisolar, lunar, solar, calendars

A note about the dating of items in Wilson’s Almanac

By Pip Wilson

This note is to explain why some dates mentioned in the Wilson’s Almanac Scriptorium or Book of Days might seem confusing or incorrect. For reasons of efficiency I have set most dates by the Gregorian calendar, generally as they occurred in 2003 or 2004 when the project began.

Some events, customs or traditions do not always take place on the same day in the calendar used in the Western world (the Gregorian calendar), which is a solar calendar that has almost completely supplanted all other calendars of the world. You can imagine how much work it would be to change non-Gregorian dates constantly – I would need NASA’s computer and a team of secretaries. (Mmmm, NASA's computer ....)

Thus, an event, custom or tradition might not be dated according to the cycles of the sun. A date might be set according to other natural phenomena, such as the motions of the moon (the next most usual calendar device) as in the Islamic calendar (see 'Id-al-Fitr  which I have placed on November 26) and in such commemorations as Poson in Sri Lanka. Then there are lunisolar (sun and moon) calendars such as the Hebrew calendar.

Other calendar customs might be dated by the behaviour of animals, birds, insects and so on, as practised in some aboriginal and other cultures. An example of this is the Bogong Moth Dreaming of the Australian Kooris (Indigenous people), which event I have also placed at November 26. Then there are special days commemorated by different groups at different times, such as International Forgiveness Day, which you will find at August 6 with a note about the variations.

In Christianity, a moveable feast (or movable feast) is a holy day – a feast or a fast – whose date is not fixed to a particular day of the Gregorian calendar year but moves in response to the date of Easter, which date varies according to a complex formula that takes into account the phases of the moon, as well as the northern Vernal Equinox of the sun. (This is also when the Neopagan Sabbat of Ostara (or Eostar) is celebrated.( Such moveable Christian feasts are Shrove Tuesday (Pancake Day) and Mid-Lent Sunday).  

On top of this, we have problems with the dating of all sorts of ancient events and customs. So when Wilson's Almanac, or any other website or 'authority', tells you that Pharaoh Thut-themostest slew 30,000 Aztecs on the Feast of the goddess Berchta's Bottyburp, which was April 19, please take it with a grain of salt. I frequently see other authorities get it wrong, and just as frequently have to make alterations to my own work. the Corrigenda page is where I announce important corrections, and where you can help me stay on the ball. Quite often a grain of salt must be taken with Roman festivals and other notable days for this same reason. And, indeed, those of many cultures.

Because the Book of Days deals with the cultures of the world, but does so with limited resources, for the convenience of the almanackist (if not the almanackee), I haven’t undertaken to change the placement of non-Gregorian calendar events and customs. On the whole, the Book of Days page into which I have entered them in 2003 or 2004 is where they will stay until such time as it’s possible to be more flexible. I trust that the reader will understand that no offence is intended to any culture or religion by this temporary arrangement, nor any confusion or misinformation.  

One more point: The Almanac is produced in Australia, but I tend to use the Northern Hemisphere seasons as that is where the majority of the Almaniacs live.

Calendar Systems (from Wikipedia)

Calendars in use on Earth are most frequently lunar, solar, lunisolar, planetary or arbitrary.

A lunar calendar is synchronized to the motion of the Moon (moon phases); an example is the Islamic calendar.

A solar calendar is based on perceived seasonal changes synchronized to the motion of the Sun; an example is the Persian calendar.

A lunisolar calendar is synchronized to the motions of both the Moon and the Sun; an example is the Jewish calendar.

A planetary calendar is a fixed period based on the number of visible moving objects in the sky; an example of this is the week.

An arbitrary calendar is not synchronized to either the Moon or the Sun; an example is the Julian day used by astronomers.

There are some calendars that appear to be synchronized to the motion of Venus, such as some of the ancient Egyptian calendars; synchronization to Venus appears to occur primarily in civilizations near the Equator. 

When is Easter?

Easter is on a different date each year according to the Northern Vernal Equinox (may fall on March 20, 21 or 22) and the phases of the moon.  By knowing Easter's date we can determine many others in the Christian calendar, such as Shrove Tuesday (Pancake Day), Ash Wednesday and Lent, Mid-Lent, and more.

From Wikipedia:

“The timing of Easter depends on the Jewish Pesach, in English Passover, which commemorates the sparing of the Hebrew first-born, as recounted in Exodus, since it is during this holiday that Jesus is believed to have been resurrected.

The date of Easter

“Easter and the holidays that are related to it are moveable feasts, in that they do not fall on a fixed date in the Gregorian calendar (which follows the motion of the Sun and the seasons). Instead, they are based on a lunar calendar like that used by the Jews. At the First Council of Nicaea in 325 it was decided that Easter would be celebrated on the Sunday after the 14th day of the first lunar month of spring (in theory, the Sunday after the first full moon on or after the day of the vernal equinox). Eventually, all churches accepted the Alexandrian method of computing Easter, which set the northern hemisphere vernal equinox at 21 March (the actual equinox may fall one or two days earlier or later), and the date of the full moon was to be determined by using the Metonic cycle. A problem here is the difference between the western churches and the Eastern Orthodox Churches. The former now use the Gregorian calendar to calculate the date of Easter, while the latter still use the original Julian calendar. The World Council of Churches proposed a reform of the method of determining the date of Easter at a summit in Aleppo, Syria, in 1997. This reform would have eliminated the difference in the date between the Eastern and Western churches. The reform was due to be implemented starting in 2001, but it failed. See Reform of the date of Easter.

“Computing the date of Easter, known as computus, is somewhat complicated. The Wiki page explains the traditional tabular methods, but also has algorithms such as the one developed by the famous mathematician Carl Friedrich Gauss.

Source: Wikipedia

 

When is it this year? One explanation can be found in Chambers:

“Easter Day is always the first Sunday after the full moon which happens upon or next after the 21st day of March; and if the full moon happens upon a Sunday, Easter Day is the Sunday after.”
Chambers, R, (Ed.), The Book of Days: A miscellany of popular antiquities in connection with the calendar, etc, W & R Chambers, London, 1881 (1879 Edition is online; See The English Year: A Personal Selection from Chambers' Book of Days)

Or, probably better:

“Easter Sunday is the Sunday following the Paschal Full Moon (PFM) date for the year.   In June 325 A.D. astronomers approximated astronomical full moon dates for the Christian church, calling them Ecclesiastical Full Moon (EFM) dates. From 326 A.D. the PFM date has always been the EFM date after March 20 (which was the equinox date in 325 A.D.).” 
Source with some explanation, and discussion of popular errors

Lunabar will put moon phases, equinoxes, solstices, etc on your desktop

The date of Easter (US Naval Observatory)

The date of Easter (Anglican calculator)

Timing of the Crucifixion and the Resurrection (Christian Churches of God)