CHRONOS

Julian Day Calculations allow you to figure out the day of the week.

Meeus, J. (1991). Astronomical algorithms. Richmond, Virginia USA, Willmann-Bell Inc., pages 60-65

timeprophecy.com - makes a nice detailed calculation of JD, Day of Week, Moonrise, Moonset, Sunrise, Sunset, etc. and is seamlessly valid for Julian and Gregorian calendar time periods

fourmilab computes JD - fourmilab computes Julian Day at UT zero hour (not 12). It has seperate entry forms for the Julian and Gregorian Calendars.

A.M. – Anno Mundi. This calendar was used by several of the Byzantine authors including Theophanes and Anastasius Bibliothecarius. The calendar is based on the Julian calendar however the year does not begin on 1 January and the starting day, month, and year of this calendar was a point of contention as it was based on an estimate for the start of "creation" (among other things) as interpreted through the Septuagint - a Greek translation of the Old Testament. An ongoing several hundred year long theological debate over when Biblical "creation" began led to multiple versions of the A.M. calendar. The earlier Byzantine sources used the Alexandrian version (A.M._a) or “Alexandrian era” of this calendar which has a starting date of 25 March 5492 BCE or, according to Bickerman (1980), 25 March 5493 BCE. Earthquake catalogers Guidoboni et al (1994) and Ambraseys (2009) assume a starting date of 25 March 5492 BCE and that is what I use. As explained by Grumel (1958:219)

The Alexandrian era of Panodorus began in 5493 BCE [and] the Alexandrian era of Annianos began in 5492 BCE. The Alexandrian Era of Annianos is what is commonly called the Alexandrian era.

Calendaric Inconsistencies of Individual Authors

Alexandrian fully QCed, Byzantine partly QCed and Chronicon Pachale not QCed

The Byzantine Calendar - wikipedia

Byzantine Creation Era Calendar

Anno Mundi Calendar Google Sheet (not fully QCed)

Indictions - An indiction (Latin: indictio, impost) was a periodic reassessment of taxation in the Roman Empire which took place every fifteen years. In Late Antiquity, this 15-year cycle began to be used to date documents and it continued to be used for this purpose in Medieval Europe. Indictions refer to an individual year in the 15 year cycle; for example, "the fourth indiction" came to mean the fourth year of the current indiction. Since the cycles themselves were not numbered, other information is needed to identify the specific year. When an ancient author supplies an indiction along with an A.M. date, the result may be greater chronological precision. For our dating purposes, indictions began in 312 CE when they were introduced by the Roman Emperor Constantine. The indiction was first used to date documents unrelated to tax collection in the mid-fourth century. By the late fourth century it was being used to date documents throughout the Mediterranean. In 537 CE, Roman Emperor Justinian decreed that all dates must include the indiction.Outside of Egypt, the year of the indiction generally began on 1 September (Bickerman, 1980:78).

Indictions - wikipedia

Chart of Indictions

Indictions Google Sheet

Regnal Years Google Sheets (not fully QCed)

The Anno Graecorum (A.G.) Calendar is also known as the Seleucid Era, Chaldean, or the Macedonian Calendar. This calendar began at the start of the Seleucid Empire and was assimilated into the Babylonian calendar with Macedonian month-names sometimes substituted for the Babylonian names (Stern, 2012:238). The A.G. calendar uses the same 19 year cycle of intercalations as the Babylonian calendar. There are two start dates. The Macedonian reckoning used by court officials in the Seleucid Empire and native Greek speakers started in the Autumn of 312 BCE with the start date eventually getting fixed to 1 Oct. 312 BCE. The Babylonian reckoning used by most Semitic speaking populations has a start date of 1 Nisan in 311 BCE. Ambraseys (2009) equates this to 1 April, Guidoboni et al (1994) equate this with 2 April, and others equate it to 3 April. A version of the A.G. calendar was used by the Christian Syriac authors such as Pseudo-Dionysius of Tell Mahre and Chronicon Ad Annum 1234. Syriac writing authors would have likely used the Macedonian reckoning as this was the standard usage among these authors for the Seleucid era (Sebastian Brock, personal communication, 2021 – see also Stern, 2012:236). In the Anno Graecorum calendar system, the day starts at sundown (Sebastian Brock, personal communication, 2022).

Syriac Calendar

Names of months and days in the Syriac Calendar

Automating the Liturgical Calendar of the Syriac Orthodox Church

A.G. Calendar Google Sheets (not fully QCed)

A.H. – Anno Hegirae is also known as the Muslim Calendar or the Islamic lunar calendar. The start date is the Hijra - when on Friday 16 July 622 CE, Mohammed and his followers migrated from Mecca to Medina. The calendar consists of 12 alternating months of 30 and 29 days. Although the original calendar determined the start of each month based on astronomical observation of the first visible crescent after a new moon, a fixed tabular calendar was developed in the 8th century CE. In the tabular calendar, a day is added to the final (12th) month during leap years making it 30 days long instead of 29. Leap days are added every 2-3 years in a 30 year cycle which is subject to local variation. The most common distribution is on the 2nd, 5th, 7th, 10th, 13th, 16th, 18th, 21st, 24th, 26th, and 29th year of each 30-year cycle (timeanddate.com). The Islamic day begins at sundown.

from fourmilab

fourmilab converts from the Islamic calendar to the Julian Calendar and vice-versa

The Islamic Calendar - timeanddate.com

Islamic Calendar Google Sheet (not fully QCed)

The Coptic Calendar is also known as the Alexandrian Calendar. The Coptic Calendar is coordinated with the Julian Calendar and, since the 4th century CE, used a starting year (Year 1) from 29 August 284 CE to 28 August 285 CE. A year consists of 13 months where the first 12 months have 30 days each followed an epagomenal month which has 5 days during normal years and 6 days during leap years. This version of the Coptic calendar is frequently called the Era of Martyrs and is frequently abbreviated as A.M. (Anno Martyrum). Coptic Leap Years are coordinated with Julian leap years however the coptic leap day is added on the last day of the coptic year rather than on 29 February. If a Coptic year will encompass a Julian Leap year (i.e. a year where there will be a February 29), the coptic year will start on 30 August instead of 29 August as 29 August in the previous Coptic year will be a leap day. In years such as this, the coptic day will be a day ahead of the Julian Calendar until 29 February. Thus, for example while 21 Tuba normally corresponds to 16 January, in a Julian Leap Year it will correspond to 17 January. The Coptic day begins at sunrise in the civil calendar and sunset in the liturgical version (Claremont Coptic Encyclopedia).

from Episteme Academy

The Coptic Calendar - Claremont Coptic Encyclopedia

The Coptic Calendar - timeanddate.com

The Coptic Calendar - wikipedia (has a great Coptic Months Table)

The Coptic Calendar by Bishoy Dawood

Converts from Julian to Coptic and other calendars

Chaine, M. (1925). La chronologie des temps chrétiens de l'Égypte et de l'Éthiopie. Paris, P. Geuthner.

The Coptic Calendar (info)

The Coptic Calendar of Martyrs at copticchurch.net

The Hebrew Calendar is also known as the Jewish Calendar or HaLuah HaIvri (הַלּוּחַ הָעִבְרִי) in Hebrew. The Hebrew Calendar is a lunisolar calendar influenced by the Ancient Babylonian Calendar which has undergone revisions over time. Initially, this calendar was based on sightings of the first crescent after the new moon. After the destruction of the 2nd temple in 70 CE and throughout the diaspora, the calendar was subject to local variations. By the 4th century CE, a calendar had emerged which was increasingly based on predicted lunar cycles. Sometime before the 8th century, a fixed 19 year Metonic cycle of intercalations similar to the Babylonian cycle was adopted and by the early 10th century, the rabbinic calendar had become like the fixed and predictable calendar that is used today. (Stern, 2012:334-335), The structure of the Hebrew Calendar is one of 12 months with an additional intercalary month added in years 3, 6, 8, 11, 14, 17, and 19 of the Metonic cycle along with a complicated set of rules (Reingold and Dershowitz, 2018:Section 8.1). The modern Hebrew Calendar is also characterized by a change in the start date of the calendar from the destruction of the second Temple in 70 CE to the start of “creation” like the Anno Mundi Calendar of the Byzantines. In the Hebrew Calendar, the day begins at sundown.

from fourmilab. This converter uses modern Hebrew Calendar rules

fourmilab converts from the Hebrew calendar to the Julian Calendar and vice-versa

Episteme Academy web page Converts from the Julian Calendar to Coptic calendar

The Hebrew Calendar - wikipedia

Stern, S. (2001). Calendar and Community: A History of the Jewish Calendar, 2nd Century BCE to 10th Century CE.. .

Seasonal Drift of the Hebrew Calendar

Hebrew Calendar Calculator

The Era of Province Arabia (also called Bostran era, the era of Bostra, the Arabian era, or Provincial era) was a calendar era (year numbering) with an epoch (start date) corresponding to 22 March 106 AD. It was the official era of the Roman province of Arabia Petraea, introduced to replace dating by regnal years after the Roman annexation of the Nabataean Kingdom. It is named after the city of Bostra, which became the headquarters of the Sixth Legion stationed in the province.

Bostran Era - wikipedia

The Era of the Olympiads was widely used in ancient texts and is based on the Greek Olympiads which were held every four years. The start date of this calendar is accepted by most modern scholars as 1 July 776 BCE (Finegan, 1998:93). Olympiads (abbreviated Ol.) are four years apart with 4 cycles specifying years within the Olympiad.

Treiger (2015) describes this as follows:

6. The Melkite Era of the Incarnation

The honor of discovering the Melkite era of the Incarnation (AInc), in use from the eleventh to the fourteenth century, belongs to Samir Khalil Samir (Samir 1987). By looking at Melkite colophons where dates “to the divine Incarnation” (li-l-taǧassud al-ilāhī) are given alongside dates according to other eras, he discovered that AInc dates are 8-9 years ahead of AD dates. The conversion key is as follows:

1 January–31 August: AInc–8 = AD;
1 September–31 December: AInc–9 = AD.

Bibliography

Samir, Samir Khalil. “L’ère de l’Incarnation dans les manuscrits arabes melkites du 11e au 14esiècle.” Orientalia Christiana Periodica 53 (1987): 193-201

The year of the Incarnation was occassionally used by Theophanes and Anastasius Bibliothecarius (when copying from Theophanes ?). It has a start date of 9 CE (Martin, 1930:12).

Martin, E. J. (1930:12). A history of the iconoclastic controversy. London, Society for Promoting Christian Knowledge.

from Clear Sky Tonight - appears to use Julian Calendar prior to 1582 CE

from Clear Sky Tonight - appears to use Julian Calendar prior to 1582 CE

from Clear Sky Tonight - appears to use Julian Calendar prior to 1582 CE

from imcee - in French - excellent. Other Calculators at imcee

from imcee - in French - excellent. Other Calculators at imcee

Ancient Astronomical Terms

Historical Glossary of Important Terms in Hellenistic Astronomy/a>

Ancient Greek Astronomy and Cosmology

The Precession of the Equinoxes Explained with Graham Hancock - youtube video

Online converters below have not been vetted

Calendarical software

Convert a Date - calendarhome.com

Calendar Utility - www.lieberknecht.de