The Heinsohn Horizon: Calendar Conundrum

A simple fact checking exercise whilst writing up one topic can produce an unexpected insight that warrants being spun off as a separate narrative.

This posting is an example of a spun off narrative.

Editing the original text to create the spun off storyline is a sobering exercise that provides a surreal replay of me stumbling blindly towards an unexpected insight.

Redrafting the original is a challenge because the spun off narrative contains elements of investigative research, accidental discovery and the unexpected insight.

As always, there is the question of whether this unexpected insight is valid.

The answer to that question is left to the individual reader to decide.

Crete Earthquake of 1303
The Crete Earthquake of the 8th August 1303 has [so we are told] been accurately dated from reports written on the day of the earthquake.

The 1303 Crete earthquake occurred at about dawn on 8 August.

Detailed information is available from reports made by representatives from Heraklion (then Candia) to the controlling Venetian administration, written on the day of the earthquake and twenty days later.

Surprisingly, the dating of the earthquake only became Settled Science 20 years ago.

Ever since the nineteenth century, the seismological tradition has offered a variety of partial interpretations of the earthquake, depending on whether the main sources used were Arabic, Greek or Latin texts.

Our systematic research has involved the analysis not only of Arab, Byzantine and Italian chronicle sources, but also and in particular of a large number of never previously used official and public authority documents, preserved in Venice in the State Archive, in the Marciana National Library and in the Library of the Museo Civico Correr.

As a result, it has been possible to establish not only chronological parameters for the earthquake (they were previously uncertain) but also its overall effects (epicentral area in Crete, Imax XI MCS).

The Large Earthquake of 8 August 1303 in Crete: Seismic Scenario and Tsunami in the Mediterranean Area – Emanuela Guidoboni and Alberto Comastri
Journal of Seismology – June 1997, Volume 1, Issue 1, pp 55–72

Equally surprising is it’s history of chronological uncertainty, duplication, assumption and assertion.

Perrey (1850, p. 19) wrongly dates the earthquake to 1304, though he gives the correct day and month. However, he points out that in the Greek and Latin sources he consulted (Pachymeris, a Byzantine writer who lived in the second half of the 13th and the early 14th century, and chronicles published in Muratori’s Rerum Italicarum Scriptores ), there were chronological uncertainties between 1302 and 1303

Mallet (1853, p. 37) gives the correct date, but expresses a degree of uncertainty about it, pointing out that some chronicles place the earthquake in 1302 or 1304.

Sieberg (1932a) … also lists an earthquake at Alexandria in 1326, but this is really the 1303 earthquake (for further critical considerations, see Ambraseys et al., 1994, pp. 43–44 and 108–109). In the section of the catalogue devoted to Crete (p. 208), the earthquake is wrongly dated to 1304, without any indication of the day or month. Two other earthquakes are listed as having occurred in 1306 and 1311, but they can, in fact, be assumed to be duplications of the 1303 event.

Plataki (1950, pp. 475–476) simply dates the earthquake to 1303, but considers the date 8 August 1304 more likely.

The Large Earthquake of 8 August 1303 in Crete: Seismic Scenario and Tsunami in the Mediterranean Area – Emanuela Guidoboni and Alberto Comastri
Journal of Seismology – June 1997, Volume 1, Issue 1, pp 55–72

Upon reflection, these “chronological uncertainties” should be expected because the Crete Earthquake of 1303 uncannily replicates the Crete Earthquake of 365 [which appears to have actually occurred at the Heinsohn Horizon which is provisionally dated to 912 AD].

The earthquake also gave rise to a large tsunami, which scholars have seen as having certain interesting elements in common with that of 21 July 365, whose epicentre was also in Crete.

The Large Earthquake of 8 August 1303 in Crete: Seismic Scenario and Tsunami in the Mediterranean Area – Emanuela Guidoboni and Alberto Comastri
Journal of Seismology – June 1997, Volume 1, Issue 1, pp 55–72



The more interesting aspect of the Settled Science associated with the Crete Earthquake of the 8th August 1303 is the observation that the Catholic and Islamic calendars were year synchronised at that point in time.

Von Hoff (1840, p. 229) used Arabic sources only, and correctly dated the earthquake to 1303 (towards the end of the year 702 of the Hegira), but he gave no indication of the day or month.

The Large Earthquake of 8 August 1303 in Crete: Seismic Scenario and Tsunami in the Mediterranean Area – Emanuela Guidoboni and Alberto Comastri
Journal of Seismology – June 1997, Volume 1, Issue 1, pp 55–72

The Islamic Calendar
Conceptually, the Islamic calendar is very much a catastrophic calendar that makes no explicit predictions about the future because it’s based upon daily lunar observations that slowly accumulate to form an historic record of past lunar months and years.

The Islamic, Muslim, or Hijri calendar is a lunar calendar consisting of 12 months in a year of 354 or 355 days.

The Islamic calendar employs the Hijri era whose epoch was retrospectively established as the Islamic New Year of AD 622.

In the West, dates in this era are usually denoted AH (Latin: Anno Hegirae, “in the year of the Hijra”) in parallel with the Christian (AD) and Jewish eras (AM)… In English, years prior to the Hijra are reckoned as BH (“Before the Hijra”).

Besides the fact that there are no leap years in Islamic calendar, if visibility of the new moon is the criterion for the beginning of each month, no month can have a monopoly of 30 days. It is not uncommon for three consecutive months to have 29 (or 30) days each in a given year. Thus the minimum difference between the real date and the one indicated in Western concordances may amount to two or three days.

The Astronomy of Ramadan – Ziauddin Sardar – New Scientist – 24 June 1982

The Islamic calendar is based on the prohibition of intercalation (nasi’) by Muhammad, in Islamic tradition dated to a sermon held on 9 Dhu al-Hijjah AH 10 (Julian date: 6 March 632). This resulted in an observation-based lunar calendar that shifts relative to the seasons of the solar year.

The observational basis of the Islam Calendar led to the development of the personal diary.

The central and most essential element of the diary was “dating” (= ta’rikh), the fixing of a date; and that date, for Islam, was the first day of the lunar month.

Now the question is, why was the term ta’rikh, generally taken to mean history, used as the word for diary?

The term ta’rikh comes from a root common to Semitic languages.

The verb (in Arabic, arrakha, warrakha) has the sense of “fixing of the month,” “fixing of the period of an event,” and, as has been suggested, “there is a vague consciousness that the word has something to do with fixing the beginning of the month.”

This last statement is fully supported by the diary of Ibn Banna’, who was careful to fix the beginning of each lunar month according to the sighting of the new crescent; and he did this even when he had nothing to record for that first day of the month.

He named the month and the day that was the month’s first day; after the twelfth month of the year, he introduced the new year stating its hijral number, the name of the first month, and the name of the month’s first day.

The fixing of the first day of the month is the only dating which appears in the diary without necessarily being followed by the recording of an event other than the month’s beginning.

The Diary In Islamic Historiography: Some Notes – George Makdisi
History and Theory, Vol. 25, No. 2 (May, 1986), pp. 173-185

In the medieval Near East, Arabic diaries were written from before the 10th century. The earliest surviving diary of this era which most resembles the modern diary was that of Ibn Banna’ in the 11th century. His diary is the earliest known to be arranged in order of date (ta’rikh in Arabic), very much like modern diaries.

Thus the present fragment of the Diary begins on Sunday the first day of the lunar month of Shauwal of the year 461, which corresponds to 3 August 1068 of the Christian era. The last entry is dated the 14th of Dhfu’l-Qa’da, 461, corresponding to 4 September 1069. There are some mistakes in the dates as set down by the author; some he corrected, and others apparently escaped his attention.

Autograph Diary of An Eleventh-Century Historian of Baghdad-I – George Makdisi
Bulletin of the School of Oriental and African Studies – Vol. 18, No. 1 – 1956

The Catholic Calendar
Conceptually, the Catholic calendar is very much a gradualist calendar that makes explicit predictions about the future based upon an unwavering faith that the Earth’s orbital period around the Sun has been [and will continue to be] a constant value.

The Gregorian calendar is the de facto international standard, and is used almost everywhere in the world for civil purposes.

It is a purely solar calendar, with a cycle of leap days in a 400-year cycle designed to keep the duration of the year aligned with the solar year.

Each Gregorian year has either 365 or 366 days (the leap day being inserted as 29 February), amounting to an average Gregorian year of 365.2425 days (compared to a solar year of 365.2422 days).

This unwavering faith in the Earth’s orbital period has meant the faithful don’t need to make daily astronomical observations nor maintain personal diaries to keep track of the date.

In the Western world, the earliest extant diary is the anonymous French Journal d’un bourgeois de Paris de 1405 a 1449.

The Diary In Islamic Historiography: Some Notes – George Makdisi
History and Theory, Vol. 25, No. 2 (May, 1986), pp. 173-185

However, the early history of the Catholic calendar is shrouded in mist and fog.

For some indeterminate period the reader of the historical narrative is left to presume the Catholic Church maintained a Liturgical Calendar that was then disseminated to the faithful.

Wikipedia, for example, provides a foggy British example of a Liturgical Calendar from one of the usual suspect sources that has a less than convincing provenance:
found in a 13th century manuscript of a collection of treatises on chess”.

The liturgical year, also known as the church year or Christian year, as well as the kalendar, consists of the cycle of liturgical seasons in Christian churches that determines when feast days, including celebrations of saints, are to be observed, and which portions of Scripture are to be read either in an annual cycle or in a cycle of several years.

Travelling back to 525 AD the reader of the historical narrative encounters Dionysius who single handedly invented the Anno Domini numbering system which he [very helpfully] bolted onto the Julian calendar and Roman chronology.

Dionysius Exiguus (c. AD 470 – c. AD 544) was a 6th-century monk born in Scythia Minor (probably modern Dobruja, in Romania and Bulgaria).

Dionysius is best known as the inventor of the Anno Domini era, which is used to number the years of both the Gregorian calendar and the Julian calendar.

He used it to identify the several Easters in his Easter table, but did not use it to date any historical event.

When he devised his table, Julian calendar years were identified by naming the consuls who held office that year; he himself stated that the “present year” was “the consulship of Probus Junior”, which he also stated was 525 years “since the incarnation of our Lord Jesus Christ”.

How he arrived at that number is unknown, but there is evidence of the system he applied.

He invented a new system of numbering years to replace the Diocletian years that had been used in an old Easter table because he did not wish to continue the memory of a tyrant who persecuted Christians.

The terms anno Domini (AD) and before Christ (BC) are used to label or number years in the Julian and Gregorian calendars.

The Julian calendar, proposed by Julius Caesar in 46 BC (708 AUC), was a reform of the Roman calendar. It took effect on 1 January 45 BC (AUC 709), by edict.

Ab urbe condita (related to anno urbis conditae; A. U. C., AUC, a.u.c.; also “anno urbis”, short a.u.) is a Latin phrase meaning “from the founding of the City (Rome)“, traditionally dated to 753 BC.

Bolting 525 AD onto Roman chronology at “the consulship of Probus Junior” was a low risk gambit as it appears next to nothing is known about “Probus Junior”.

Prosopography of the Later Roman Empire (usually abbreviated as PLRE) is a set of three volumes collectively describing many of the people attested or claimed to have lived in the Roman Empire from AD 260, the date of the beginning of Gallienus’ sole rule, to 641, the date of the death of Heraclius, which is commonly held to mark the end of Late Antiquity.

Sources cited include histories, literary texts, inscriptions, and miscellaneous written sources.

Claiming the Anno Domini numbering system was invented in 525 AD is a far more difficult assertion to swallow as it took nearly 900 years to roll-out the system in Western Europe.

According to the Catholic Encyclopedia, popes continued to date documents according to regnal years for some time, but usage of AD gradually became more common in Roman Catholic countries from the 11th to the 14th centuries.

In 1422, Portugal became the last Western European country to switch to the system begun by Dionysius.

The regnal year of the emperor was also used to identify years, especially in the Byzantine Empire after 537 AD, when Justinian required its use.

Bolting 525 AD onto the Julian calendar would have been a very low risk option if it wasn’t for the Gregorian Calendar Reform.

Gregorian Calendar Reform
In 1582 the Catholic calendar was reformed to align with the equinoxes and solstices.

In so doing the calendar lost 10 days by jumping directly from 4th to 15th October 1582.

The motivation for the reform was to stop the drift of the calendar with respect to the equinoxes and solstices – particularly the northern vernal equinox, which helps set the date for Easter.

Transition to the Gregorian calendar would restore the holiday to the time of the year in which it was celebrated when introduced by the early Church.

When the new calendar was put in use, the error accumulated in the 13 centuries since the Council of Nicaea was corrected by a deletion of 10 days.

The Julian calendar day Thursday, 4 October 1582 was followed by the first day of the Gregorian calendar, Friday, 15 October 1582 (the cycle of weekdays was not affected).

The academic argument used to explain away the “deletion of 10 days” is the difference between the number of days in the Julian calendar [365.25] and the Gregorian calendar [365.2425].

The Gregorian calendar is internationally the most widely used civil calendar.

The Gregorian calendar improves the approximation made by the Julian calendar by skipping three Julian leap days in every 400 years, giving an average year of 365.2425 mean solar days long.

But the deleted “10 days” can’t be reconciled with a Julian calendar formulated in 46 BC.

This led Heribert Illig to conclude the Catholic calendar includes [about] 300 phantom years.

By the time the Gregorian calendar was introduced in AD 1582, Illig alleges that the old Julian calendar should have produced a discrepancy of thirteen days between it and the real (or tropical) calendar.

Instead, the astronomers and mathematicians working for Pope Gregory XIII had found that the civil calendar needed to be adjusted by only ten days. (The Julian calendar day Thursday, 4 October 1582 was followed by the first day of the Gregorian calendar, Friday, 15 October 1582).

From this, Illig concludes that the AD era had counted roughly three centuries which never existed.

However, this reconciliation failure suggests there are other possibilities:

a) The Julian calendar was compromised by the Earth experiencing an orbital excursion.
b) The Julian calendar was not a solar calendar.

Either way, it’s possible the deleted “10 days” from the Catholic calendar may represent the tip of the iceberg for a calendar error encompassing one, or more, years.

The Coligny Calendar
The 2nd century AD Coligny Calendar is an academic curiosity that I stumbled upon whilst researching the solar credentials of the Julian calendar.

The so-called “Calendar of Coligny” is a fragmented bronze plaque that was found in 1897 in the remains of a Roman Temple of Apollo in Coligny, Ain, France.

As a “Celtic” calendar, there are a few problems with it, not the least of which is the uncertainty that it is, in fact, either a Calendar or “Celtic”.

Both are plausible assumptions, but remain essentially unproven.

Coligny Calendar – Marc Carlson – 9 June 2004

The Coligny Calendar is generally said to be a lunisolar calendar with intercalary months.

The Coligny calendar is a Gaulish peg calendar or parapegma made in Roman Gaul in the 2nd century, giving a five-year cycle of a lunisolar calendar with intercalary months.

It is the most important evidence for the reconstruction of an ancient Celtic calendar.
It is written in Latin inscriptional capitals and is in the Gaulish language.

The restored tablet contains sixteen vertical columns, with 62 months distributed over five years.

It shows 12 repeating units comprised of alternating 29 and 30 lesser units, and so appearing to correspond to the 13 lunar months of the solar year made up of 29 or 30 days.

Coligny Calendar – Marc Carlson – 9 June 2004

But beneath all the fevered speculation about intercalary months lies a 2nd century AD calendar from Roman Gaul that “yields a total of 354 or 355 days” just like the Islamic lunar calendar.

It should be noted that this calendar would yield a total of 354 or 355 days (as one month alternates its length)…

Coligny Calendar – Marc Carlson – 9 June 2004

The Islamic, Muslim, or Hijri calendar is a lunar calendar consisting of 12 months in a year of 354 or 355 days.

Furthermore, this 2nd century AD calendar from Roman Gaul “yields a total of 354 or 355 days” just like the pre-Julian civil year in Rome.

The unattested but almost certain lunar year and the pre-Julian civil year were 354 or 355 days long, with the difference from the solar year more or less corrected by an irregular intercalary month.

This calendar of 354 or 355 days is about 10 days shorter than a Solar calendar.

That sounds familiar!

This calendar of 354 or 355 days isn’t ideal for planning seasonal agriculture activities or religious services that are aligned with the equinoxes and solstices.

That rings a bell!

Is it possible the Gregorian Calendar Reforms marked the transition of the Catholic calendar from a Lunar to a Solar based system?

Is it possible the Julian calendar was really a lunar calendar?

If that were the case then the official era of the Julian calendar [45 BC – 1582 AD] represents an accumulated difference of between 45 and 50 years when compared to the Gregorian calendar.

Either way, the erection of the Vatican Obelisk in 1586 suggests the Vatican was determined to emphasise it’s solar orientation in the era of the Gregorian Calendar Reform.

St. Peter’s Square is a large plaza located directly in front of St. Peter’s Basilica in the Vatican City, the papal enclave inside Rome, directly west of the neighbourhood or rione of Borgo.

At the center of the ovato tondo stands an uninscribed Egyptian obelisk of red granite, 25.5 metres tall, supported on bronze lions and surmounted by the Chigi arms in bronze, in all 41 metres to the cross on its top. The obelisk was originally erected at Heliopolis, Egypt, by an unknown pharaoh.

It was moved to its current site in 1586 by the engineer-architect Domenico Fontana under the direction of Pope Sixtus V; the engineering feat of re-erecting its vast weight was memorialized in a suite of engravings.

In 1817 circular stones were set to mark the tip of the obelisk’s shadow at noon as the sun entered each of the signs of the zodiac, making the obelisk a gigantic sundial’s gnomon.

These were troubled times where the Protestant Reformation provoked the incumbents to double-down with their own Catholic Revival.

The Reformation, specifically referred to as the Protestant Reformation, was a schism from the Catholic Church initiated by Martin Luther and continued by John Calvin, Huldrych Zwingli, and other early Protestant Reformers in 16th-century Europe.

It is usually considered to have started with the publication of the Ninety-five Theses by Luther in 1517 and lasted until the end of the Thirty Years’ War with the Peace of Westphalia in 1648.

The Counter-Reformation, also called the Catholic Reformation or the Catholic Revival, was the period of Catholic resurgence initiated in response to the Protestant Reformation, beginning with the Council of Trent (1545–1563) and ending at the close of the Thirty Years’ War (1648).

And as they say: In war, truth is the first casualty.

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9 Responses to The Heinsohn Horizon: Calendar Conundrum

  1. There’s more than a conundrum – if the Julian calendar was lunar, then when did the Church start noticing the discrepancies? Same with the implementation of the Julian system – it was put in place because the previous system became inaccurate. Then it worked until when? The next perturbation of the Earth’s motion caused by externalities. That’s the 610 AD Libby mark.

    Gunnar is right that there was one catastrophe from the stratigraphy, and Illig is right with his 300 year anomaly.

    So identifying the massive spike in the Libby data chronologically seems necessary.

    It would nice if more data on the Garzweiler Pit roman aqueduct could be found. Unless there’s been secret photoshopping of images, Hagedoorn’s photos strongly suggest the Roman water works were buried under Miocene sediments. That makes it geologically which event? Not the Little Ice Age as that seems to be tied up with the 16th century political situations in Europe, but perhaps the Earth experienced a slight shift in geometry?

    Medieval warm period was coined by the late UK climate scientist Lamb. IPCC scientists made this disappear. Lamb based his interpretation on documents assumed to be of the time. Did he make a rash assumption ?

    Back to the drawing board!

    • malagabay says:

      When did the Church start noticing the discrepancies?

      Same thought crossed by mind… so I’ll do some digging.

      • Copernicus noticed it, and I wonder if he referred to any earlier observation. Possibly related but my family history starts AD1326 when there were 5 families of our name in the church records (Netherlands Deventer vicinity), before that nothing so <1326 AD has to correlate with some large scale disaster or tail end of one affecting Europe. This should supply a starting date for Church activities or problems with timing.

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  3. An interesting subject, considering that the 300 years or so are really dark in history. However, in respect of the island of Malta – ancient Melite- there are still a couple of mentions in documents from those presumed added dates. The island was so unimportant in those dark days that faking such data, I think, would have been unthinkable. Still — interesting.

    The subject gets a mention in this link; long but go straight to the last posts by ‘curtisclay’.;all

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  6. Karl-Heinz Lewin says:

    Very interesting and exciting, from the beginning until the spot where “the bell rang”, where the argumentation started to become unreasonable speculation. Cassius Dio and others reported that Julius Caesar replaced the lunisolar Roman calendar by a solar calendar which he had brought with him from Alexandria, and there is no indication that the length of of the Julian year or its leap rule was ever changed after the last modification by emperor Augustus.

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