Friday, July 16, 2021

Medieval Astronomy

The Syriac Text
The reconstructed sky in the place where the Syriac text was written on May 25, 760 at 2:40 a.m.

Scientists have
analyzed ancient historical accounts from Syria, China, the Mediterranean and West Asia (most critically, the detailed accounts in the hand written Syrian Chronicle of Zuqn¯ın, part of which ended up in the Vatican Library and part of which ended up in the British Museum) to confirm that all of these accounts viewed key parts of the appearance of a particular comet in their skies in late May and early June of the year 760 CE.  

The scientists matched these observations with calculations of where the comet 1P/Halley would have been in the sky at that time based upon its current observed trajectory with key dates pinned down to a margin of error of one to two days for particular events.

This 760 CE fly-by was the comet's last return before a close encounter with Earth in 837 CE. The 760 CE perihelion of the comet that was observed is particularly important for extrapolation further back in time. This study provides one of the longest time frames of confirmed continued observations of the same celestial object. This helps to confirm the accuracy and robustness of astronomy's current gravitational calculations of solar system orbits, and to remind us just how long quite accurate scientistic astronomy observations have been collected and recorded by people.

Historical Context

This was near the end of the period known as the "dark ages" in the former western Roman Empire in Europe, during the life of Charlemagne, eight years before he began his reign as the King of the Franks in what is now France, and forty years after the remarkably wet summer of 720 CE in Europe.

Decisive battles on land and at sea with the Byzantine Empire ended the expansion of the Umayyad Caliphate into the territory of the former Roman Empire fourteen years earlier (746 CE). The Eastern Orthodox Christian Byzantine Empire was the last remnant of the Roman Empire, in what is now most of Turkey, Greece and Italy, and would persist in a gradually diminished form over about three more centuries. The West Asian accounts were written by Byzantine subjects.

As the body text of the new paper explains:
The author of the chronicle was probably the stylite monk Joshua; a stylite is an early Byzantine or Syrian Christian ascetic living and preaching on a pillar in the open air, so that many celestial observations can be expected in his work. The author of the Chronicle of Zuqn¯ın may have lived on a pillar for some time. During the time of writing of the Chronicle of Zuqn¯ın [ed. completed in 775/776 CE], the area was outside the border of the Byzantine empire and already under 푐Abbasid rule.
Thus, the Syrian chronicle entries were written by a Christian monk under the jurisdiction of the Islamic Abbasid Caliphate (750-1517 CE) in areas recently reclaimed by the Caliphate after a brief Byzantine expansion into the territory of the Umayyad Caliphate which preceded it. The Abbasid Caliphate had been formed ten years earlier in the Abbasid Revolution and replaced the Umayyad Caliphate (661-750 CE). The Umayyad Caliphate had been led by an ethnically Arab elite that treated even non-Arab Muslim converts as second class citizens, while the Abbasid Caliphate was led by a multi-ethnic, mostly non-Arab, and eastern oriented Abbasid Caliphate that ruled in a more inclusive manner, whose Caliphs claimed to have descended from an uncle of the Prophet Muhammad (who died about four decades before the comet appeared).

The provenance of the Chronicle was somewhat involved. As the body text explains:
The Chronicle of Zuqn¯ın is not known to be copied and disseminated; sometime during the 9th century it was transferred to the Monastery of the Syrians in the Egyptian desert . . .  Shortly after the manuscript was found and bought for the Vatican, it was considered to be written by the ¯ West Syrian patriarch Dionysius I of Tell-Mah. re, so that this chronicle was long known as Chronicle of Dionysius of ¯ Tell-Mah. re. Dionysius did write an otherwise lost world chronicle, but lived later (died AD ca. 845). Since this mistake was noticed, the chronicle has been called the Chronicle of Pseudo-Dionysius of Tell-Mah. re or, better, the Chronicle of Zuqn¯ın, because the text mentions the monastery of Zuqn¯ın as the living place of the author; Zuqn¯ın was located near Amida, now Diyarbakır in Turkey near the border to Syria. 
The Chronicle of Zuqn¯ın is made of four parts: Part I runs from the creation to Emperor Constantine (AD 272-337), Part II from Constantine to Emperor Theodosius II (AD 401-450) plus a copy of the so-called Chronicle of PseudoJoshua the Stylite (AD 497 to 506/7), Part III from Theodosius to Emperor Justinian (AD 481-565), and Part IV to the time of writing, AD 775/776. The Chronicler used a variety of sources, some of them otherwise lost. The author knew that some of his sources did not provide a perfect chronology; for him, it is more important to convey his message (to learn from history) than to give perfect datings. 
The events reported in the text are dated using the Seleucid calendar; the Seleucid Era (SE) started on October 7, BC 312 (= Dios 1). There are several versions of the Seleucid calendar, including the Babylonian (Jewish), Macedonian, and West Syrian (Christian) ones. The author of our chronicle systematically used the latter version for reports during his lifetime – a solar calendar, in which the year ran from Tishri/October 1 to Elul/September 30, applied since at least the fifth century AD.
This was also two years before the city of Baghdad was founded within the Abbasid Caliphate, near the ancient city of Seleucia, which had been the capitol of the Nestorian Christian Church of the East from 410 CE, until it had to be abandoned to the desert sands when the Tigris River that made it possible to live there shifted, a few decades after Baghdad was founded.

In China, this comet's appearance coincided with the unsuccessful seven year long An Lushan Rebellion against the Tang Dynasty. This rebellion ended with a pair of stunning betrays, first when An Lushan, the leader of the rebellion, was killed by one of his own eunuchs in 757, and then when his successor as leader of the rebellion, Shi Siming, was killed by his own son in 763, which ended the rebellion.

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