An astronomical murder?

Transcription

1 An astronomical murder? Ari Belenkiy examines the murder of Hypatia of Alexandria, wondering whether problems with astronomical observations and the date of Easter led to her becoming a casualty of fifth-century political intrigue. 1: Portrait of Hypatia. (Elbert Hubbard 1908 Little Journeys to the Homes of Great Teachers 23 [4] [East Aurora, New York: The Roycrofters]) The murder of the scholar Hypatia of Alexandria has never been adequately explained. I propose that she became a victim of a political cataclysm stemming from disagreement within the Roman Empire on the date of Easter in AD 417, after she provided critical expertise in astronomy relating to the vernal equinox. Atmospheric refraction, a phenomenon unknown to Hypatia, could have led her to conclude that the equinox fell on 16 March, the date agreeable to the Roman church, rather than on 21 March, the date championed by Alexandria. Her position could have threatened the Alexandrian church s established authority in the matter of dating Easters for the whole of the Roman Empire. I argue that this political threat led a Christian mob to kill her. As a corollary, this argument tips the scale in favour of year 416 for her date of death, rather than 415 as the majority hold. In addition, I suggest that she died on 21 March. Hypatia s life and death are known from contemporary accounts, mainly from the writings of Socrates Scholasticus (see Hypatia s life p2.10. She was a scholar of high repute, whose death in the early part of the fifth century (usually suggested as taking place in 415 or 416) arose in some way from a disagreement between Orestes, the Imperial Prefect of Alexandria, who ruled as part of the Roman Empire, and Cyril, Bishop of Alexandria, whose power came from his position in the Alexandrian church. At around the same time as Hypatia s death, there was a Christian Jewish clash in Alexandria that led to the expulsion of the Jewish community from the city. Despite there being extensive literature on the subject (Dzielska and Lyra 1995, Deakin 2007, Berggren 2009), historians have discovered no serious reason for a disagreement between Orestes and Cyril that could lead to violence against the former, nor a compelling reason for Hypatia s murder, nor anything more than a somewhat superficial reason for the religious unrest. No-one has attempted to discover the subject of her frequent interviews with Orestes. General references to Cyril s dislike for the dissidents among the Christians cannot explain the brutal murder his followers inflicted on Hypatia. After all, Theophilus, Cyril s predecessor and uncle, co-existed peacefully with all parties for many years. It seems likely that these hostilities were the consequence of a particular controversy that caught up the different groups of Alexandrian society. The problem was surely related to astronomy: the sixth-century Hesychius of Miletus in his Nomenclature or Index of Famous Persons in Learning writes, for example, that Cyril s envy was caused by Hypatia s extraordinary wisdom and skill in astronomy. Astronomy is a key word here. John, an Egyptian Coptic Bishop of Nikiu (fl. 696), also mentions (albeit cursorily) Hypatia s skills in astronomy in his Chronicle : And in those days there appeared in Alexandria a female philosopher, a pagan named Hypatia, and she was devoted at all times to magic, astrolabes and instruments of music, and she beguiled many people through satanic wiles. Although satanic wiles are not defined, an astrolabe is a concrete object dealing with measuring the positions of the stars. Though none of the historians writing about Hypatia have mentioned astronomy as a reason for her murder, I will build my case on the fact that the state administrator (Orestes) was involved, which raises the problem to the level of Empire, and that it bore some relation to astronomy. The problem that best seems to satisfy these constraints in fifthcentury Alexandria was the date of Easter. Uncertain dates It is generally accepted that Easter is the first Sunday after the first full Moon falling on or after the day of the vernal equinox (the first vernal full Moon). In the first quarter of the fifth century, the vernal equinox fell on 19 or 20 March, so Easter would be expected to take place on or after these dates. But at that period, two major churches used different criteria for determining the date of Easter. As a result, in 417 the Roman church celebrated Easter in March, while Alexandrian Christians observed it in April. Such a disagreement points to a power struggle between Rome and Alexandria. Could Hypatia have been at the heart of this political battle and, as an eminent astronomer, perhaps have been charged with determining the date of the vernal equinox? A&G April 2010 Vol

2 Hypatia s life: information from contemporary histories The details we have of Hypatia s life and death come from contemporary accounts. Damascius (c. 458, died after 538), who was known as the last of the Neo-Platonists wrote about her in Vita Isidori, a text that survives thank to being preserved and reproduced in the Suda, a 10th-century Byzantine chronicle: Hypatia was born and educated in Alexandria. Since she had greater intelligence than her father, she was not satisfied with his instruction in mathematical subjects and she devoted herself diligently to philosophical studies. This woman used to put on her philosopher s cloak and walk through the middle of town. She publicly interpreted Plato, Aristotle, or the works of any other philosopher for everybody who wished to hear her. In addition to her expertise in teaching she rose to the pinnacle of civic virtue. Socrates Scholasticus of Constantinople (b. 380) recounts details that make it fair to assume that he heard the story in Constantinople some years after the murder, from an eyewitness and resident of Alexandria, who was too young in 416 to grasp the scientific underpinning of contemporary events. He writes about Hypatia s death in his Historia Ecclesiastica, finished c. 439 (HE VII. 15): There was a woman at Alexandria named Hypatia, daughter of the philosopher Theon, who made such attainments in literature and science, as to far surpass all the philosophers of her own time... Yet even she fell victim to the political jealousy which at that time prevailed. For as she had frequent interviews with Orestes [Imperial prefect of Alexandria], it was calumniously reported among the Christian populace that it was she who prevented Orestes from being reconciled to the bishop [Cyril of Alexandria]. Some of them, therefore, carried away by a fierce and bigoted zeal, whose ringleader was a reader named Peter, waylaid her returning home, and dragging her from her carriage, they took her to the church called Caesareum, where they completely stripped her, and then murdered her with tiles. After tearing her body in pieces, they took her mangled limbs to a place called Cinaron, and there burnt them. This affair brought not the least opprobrium, not only upon Cyril, but also upon the whole Alexandrian church. And surely nothing can be farther from the spirit of Christianity than the allowance of massacres, fights, and actions of that sort. This happened in the month of March during Lent, in the fourth year of Cyril s episcopate, under the tenth consulate of Honorius, and the sixth of Theodosius. Other sources include John Malalas (a Byzantine chronicler from Antioch, c ) and Philostorgius (a so-called Anomoean Church historian, 368 c. 439). To pursue this idea, it is important to know the date of Hypatia s death. There is evidence that it took place in either 415 or 416. The account by Socrates (see box Hypatia s life ) includes the words in the fourth of Cyril s episcopate, under the tenth consulate of Honorius and the sixth of Theodosius which are problematic. Cyril was ordained in October 412, so the first part points to year 416, but the consulate years point to 415. Baronius, the church historian, in his Annales Ecclesiastici ( ) chose 415 as the date of the murder. The problem was thoroughly discussed by German historians, Wernsdorf (1748), Wolf (1879) and Seeck (1921), who argued that the murder took place in March 416, because otherwise there would have been one and one-half years between the murder and Emperor Theodosius s decree of 5 October 416, which is usually seen as a reaction to the riots in Alexandria. Seeck claimed that the nomination of consuls was often delayed during the fifth century, which led to the increased use of postconsulates (i.e. the year is given as the year after the tenure of a particular pair of men). Socrates may have confused the post-consulate of the consuls of 415 with their actual consulate. Seeck admitted that there was also a possibility that Theodosius s decree is wrongly dated. Hoche (1860) retorted that one and one-half years is a reasonable time span and there is no reason to put the consular dating into doubt. He suggested it is more likely that the years of Cyril s tenure as a bishop were synchronized with the Roman calendar (i.e. since both consular and Episcopal years run from 1 January, the fourth year would be AD 415 in the Julian calendar). Mueller (1987) puts Hypatia s death in March 415 as the one virtually certain date in the life of Hypatia and that the only reasonable alternative, March 416, is generally rejected. Other dates also have been favoured, e.g. van der Waerden (1956) suggests 418. All of these arguments are conditional on external circumstances, such as Theodosius s decree; no independent reason has so far been offered. I propose that Hypatia was murdered in 417, on the basis of astronomical data and her known position of eminence among astronomers in the region. The years under discussion provide a first clue I suggest that Hypatia s murder is related to the conflict between the churches of Rome and Alexandria regarding the date of Easter 417. Easter and Alexandrian astronomy According to the modern formula, Easter falls on the first Sunday after the first vernal full Moon where vernal means on or after the vernal equinox. Yet it is not known when this definition was adopted all we have in hand are fourth and fifth-century calendar tables. Roman Easters were computed following an 84-year cycle (Mosshammer 2008), and the Alexandrian Easter followed a simple 19-year cyclic calendar (Neugebauer 1979, Belenkiy 2002). There was a further complication in the Roman church: if the full Moon fell on a Saturday, Easter could not be celebrated until a week later. The tables show that in the fourth and fifth centuries, the Roman and Alexandrian churches allowed for two quite different dates for the earliest Easter full Moon: 16 March and 21 March, correspondingly. The reason for two dates has never been clearly stated; they seem to be simple artifacts of the calendar cycles that each church followed: 84 years (Roman) and 19 years (Alexandrian). It is known, however, that the Roman church wanted to have Easter before 21 April, the day of foundation of Rome. This explains Rome s insistence on the early dates for the Easter full Moon though Rome was diligent to have Easter not earlier than 21 March. On the other hand, it seems that the Alexandrian church wanted Easter full Moons to fall after the vernal equinox. Eusebius of Caesaria (c ) in Historia Ecclesiastica (HE 7.20) says that Dionysius, patriarch of Alexandria in the midthird century, used a rule that Easter Sunday could not occur before the equinox. Eusebius (HE ) also says that the equinox rule was reformulated by Anatolius of Laodicea in the late third century to mean that an Easter full Moon must not fall before the equinox. If so, the Roman computus followed the former rule, while the Alexandrian used the latter. The Alexandrian church was considered expert in the date of Easter by the Nicene Council in 325, perhaps because they had a working knowledge of Ptolemy s Syntaxis (better known by its Arabic name Almagest) and the precession of the equinoxes. Indeed, in the letter to Emperor Marcian regarding another problematic Easter, that of 455, Pope Leo the Great 2.10 A&G April 2010 Vol. 51

3 Table 1: Duration of daytime in AD 415 and 416 on March AD 415 AD 416 sunrise zenith sunset duration sunrise zenith sunset duration 15 Mar 06:10 12:09 18:09 11:58 06:09 12:09 18:09 11:59 16 Mar 06:09 12:09 18:09 12:00 06:08 12:08 18:10 12:01 17 Mar 06:08 12:08 18:10 12:02 06:07 12:08 18:10 12:03 18 Mar 06:06 12:08 18:10 12:04 06:05 12:08 18:11 12:05 19 Mar 06:05 12:08 18:11 12:06 06:04 12:07 18:11 12:07 20 Mar 06:04 12:07 18:12 12:07 06:03 12:07 18:12 12:09 21 Mar 06:02 12:07 18:12 12:09 06:01 12:06 18:13 12:11 Computed with Project Pluto Guide 8 software wrote that the Holy fathers, in order to remove any occasion for error delegated all care to the Alexandrian bishop, since there was among the Egyptians an ancient science for the computation (Krusch 1880, Mosshammer 2008). It seems that both churches held 21/22 March as a borderline. Let me show how a fourthcentury follower of Ptolemy might have arrived at these dates for a vernal equinox: Ptolemy fixed the vernal equinox in 140 on 22 March 13h AT (AT = Alexandrian local time). In 325, the Alexandrian church, revising the calendar foundations, ought to have shifted forward Ptolemy s time for the vernal equinoxes by about 14.8 hours, following Ptolemy s assertion that equinoxes slip down the Julian calendar by one day in 300 years, and therefore getting the spread between 21 March 22h AT (in leap years), and 22 March 16h AT (in preleap years). Astronomy in the fifth century Finding the true vernal equinox could have been a touchy problem in the fourth and fifth centuries, for the Christian church suspected that the art of astronomy was practised in tandem with paganism. Therefore, Ptolemy s data were relied on for many years. The only astronomer of note in that epoch was Theon of Alexandria, Hypatia s father, who is known to have observed a solar and a lunar eclipse in 364 (Delambre 1817, Rome 1950). Theon, it seems, was not a practical astronomer; he added a commentary to Syntaxis and to Ptolemy s Handy Tables, without any revision of its parameters signalling his approval of Ptolemy s position of the equinoxes and the rate of precession. Still, in the commentary to the Handy Tables, Theon mentions a theory of the trepidation of equinoxes which suggests that the equinoxes make a short backand-forth movement instead of a slow steady change (Delambre 1817). Whatever the value of the theory (a sort of theoretical escape from this astronomical dead end) it demonstrates the late fourth century unhappiness with Ptolemy, particularly over the speed of precession. An observer looking for the equinoxes at the turn of the fifth century could not have failed to notice a problem with Ptolemy s rate of succession. The equinoxes slipped down the Julian calendar more than twice as quickly as Ptolemy had postulated: moving by one day in 129 years rather than Ptolemy s one day in 300 years. Since Ptolemy himself fixed the vernal equinox in the year 140 at 20.5 hours later than it must have been (21 March 16:23 AT), the true equinox in the 410s fell more than two days earlier than Ptolemy s tables suggested. Modern ephemeris put the equinox on 20 March 07:14 AT in 415 and 19 March 13:04 AT in 416. Even discarding one-third of a day for precision in observing the equinoxes by ancient Greek astronomers (Newton 1977), any observers would have disagreed with those who computed positions of the equinoxes from the Syntaxis by about two days. If this discrepancy were known, the true dates of the equinoxes could possibly undermine the Alexandrian authority over the Easter computus, certainly in the years when the Roman Easter full Moon was set on 19 or 20 March. But could an observer of the time pin down the equinoxes? There were two quite different ways to find the equinoxes for an observer of Hypatia s time. The first was to follow Ptolemy s method in Book I of Syntaxis, by erecting a relatively large metal meridian ring or a quadrant, subdivided into degrees and further in as many parts as possible, and observing the Sun s passages at noon for several consecutive days in March. The vernal equinox falls on the day when zenith distance of the Sun is equal to the latitude. The latitude of Alexandria, 30 58, was well known to Ptolemy and astronomers after him. Since observations are performed only at noon, to find the precise time of the equinox one had to interpolate between the two points of passage. Was this option available to Theon and Hypatia? The ring or the quadrant had to be established outside the house, where it would be exposed to others eyes. As a consequence, the instruments and the procedure of observing the sky would have been visible, and suspicious in the eyes of Christian zealots, which might have been dangerous for an observer. This seems an unlikely scenario in Hypatia s time, when Christians were the dominant force in Alexandria. There is, however, a second and simpler procedure to find the day of the equinox by observing the times of sunrise and sunset every day. On the day when these events are separated by 12 hours (plus or minus a minute or two), the daytime would be equal to nighttime as is required by the very definition of the equinox. Having a good sand or water clock at home would not have been that suspicious and was all one needed to find the date of the equinox, provided the observer understood the basic astronomical definitions. If Hypatia had observed the sunrises (for the first appearance of the disc) and sunsets (the last appearance of the disc) she would have obtained the data shown in table 1. As a competent astronomer, Hypatia could have then subtracted the time needed for the Sun to topple half its own disc. The Sun s disc is 32 in diameter. Because the Sun covers 360 in every 24 hours, and hence 1 for 4 minutes, the time amounts to one minute and four seconds on each end. This would have brought her attention to 17 March, where the duration of daytime was 12:02 in 415 or 12:03 in 416 and which, after subtracting the two minutes, would have been close to 12:00. This fact lies at the heart of the definition of equinox. She easily could have convinced anyone with common sense that 17 March was the date of the equinox for non-leap years (like 415, 417), while in leap years (like 416) it could have slipped down, even to 16 March. But there is a further phenomenon that would affect the date of the equinox for a fifth-century observer such as Hypatia: atmospheric refraction, which always leads to a lengthening of true daytime by several minutes on both sides, at sunrise and sunset. The bending of light rays is negligible for observing the Sun high in the sky, but amounts to 33 at the horizon (calculated for Alexandria, where the temperature in mid-march is 20 C and the atmospheric pressure is 1 atmosphere; Meeus 1991). The Sun needs 2.25 minutes to cross this arc, on either side, making 4.5 minutes altogether. The Syntaxis is silent on atmospheric refraction, apart from one dubious mention in Book IX (Toomer 1998). True, Ptolemy mentioned this effect for observing the stars in his Optics, and Cleomedes knew that the Sun must still be visible below the horizon (Mahan 1962, Ross 2000), but we have no hint that Hypatia was acquainted with Optics and Cleomedes On the Circular Motions of the Celestial Bodies. No-one who writes on Hypatia mentions Cleomedes name. It is not even clear when and A&G April 2010 Vol

4 where he lived (Neugebauer 1941). If Hypatia had known about atmospheric refraction, she would certainly have looked for the equinox on the dates when daytime lasted for 12:06 or 12:07 hours: 19 or 20 March. Theon and Hypatia Was Hypatia a competent practical astronomer, able to work with a ring or a quadrant? We don t know. Was she acquainted with the problem of the precession of the equinoxes? The answer yes comes from the fact that she collaborated with her father Theon on the commentary to Syntaxis, specifically Book III, which deals with the Sun s motion (Cameron 1990). So the idea of the equinoxes moving across the Julian calendar would not have been a stumbling block for her. Such a theoretical background is more than enough to fulfill the second scenario above to find the day of the equinox with a water or sand clock. To prove the historicity of the first scenario observations with a meridian ring or quadrant is much more difficult. We know that Theon made observations of the solar and lunar eclipses in 364. If he had attempted to construct the ring and observe the time of the equinoxes, armed with the Syntaxis, he would certainly find the correct time within half a day. Although we are unaware of such observations, and Theon s commentary on Syntaxis as well as his edition of Ptolemy s Handy Tables does not bear any mark of them, they would be natural extensions of Theon s astronomical activities. If he had continued his work in this way, no doubt Hypatia would be aware of his findings. Then she would have certainly arrived at the correct dates, 19 March for 416 and 417 or 20 March for 415. And because this scenario requires observing the Sun at zenith, atmospheric refraction would not play any role. But again, there is no evidence that she did so. My guess is that Hypatia observed the time of sunrises and sunsets in 415 and 416, using a very good clock, and convinced herself and the Prefect, Orestes that the true vernal equinox fell on 16 or 17 March, quite far from the established date of 21 March. This fact, combined with the Alexandrian definition of Easter, would allow the first vernal full Moon to fall between 17 March and 20 March, permitting an early Easter in 417. Accepting the 17 March equinox as the true one, Easter 417 in Alexandria ought to have been celebrated on 18 March, which would have been not only earlier than the Roman date, 25 March, but even before their vernal equinox a complete humiliation for the Alexandrian church! The Prefect s report on the issue would certainly matter to the Emperor and could bring unpredictable consequences to the Empire as a whole; in fact, Alexandrian hegemony in the Easter calendar could have been undermined or even extinguished. The equinox problem in the open The problem burst into the open in or immediately prior to 417, when Rome intended to celebrate Easter on 25 March, but Alexandria prepared to observe it on 22 April. This event even the expectation of it must have caused much psychological and political turmoil, since even years later the next generation of Christian clergy still spoke of it with bitterness, as one may see from the letter of Bishop Proterius to Pope Leo (below). If Hypatia was murdered because it was her advice that led to this difference between Rome and Alexandria over the date of Easter, when did the murder happen? My argument favours 416. Cyril certainly continued his uncle Theophilus s tradition (originating with St Athanasius in the fourth century) of issuing annual Festive Paschal letters that gave the date of Easter for the next year (Mosshammer 2008). The letters were dispatched all over the Empire in the autumn, to be read on Epiphany (6 January), but they were likely to have been written earlier, although the exact date was probably decided on around the previous Easter. Did it happen that, in 416, seeing the opposition from Orestes to the Alexandrian date of the next (417) Easter, and fearing that the Christian world would be divided in celebrating Easter, Christian zealots decided to solve the problem by murdering the person they perceived as the major cause of the problem? The year 415 seems too distant from 417 to ignite such passion. Socrates says the murder happened in March, during Lent, at a place called Cinaron. Easter in 416 was on 2 April. Lent in Alexandria must have been over by 24 March, the last Friday before Palm Sunday. If Hypatia were to convince Orestes that 21 March was not the equinox, she might have continued her observations up to and including 21 March. I suggest therefore that 21 March is the most likely day for her murder. Cinaron could have been the place where Hypatia performed her observations and therefore chosen by Cyril s zealots as the place of her final disposal. As a matter of fact, John of Nikiu provides a curious detail: And thereafter a multitude of believers in God arose under the guidance of Peter the magistrate and they proceeded to seek for the pagan woman who had beguiled the people of the city and the prefect through her enchantments. And when they learnt the place where she was, they proceeded to her and found her seated on a (lofty) chair Might this reference to a lofty chair suggest that Hypatia was involved in astronomical observations? It seems a possible interpretation. Cyril became Bishop in October 412 and had a potential threat to face in 414. The Roman Easter full Moon was on 20 March (Friday), and Rome celebrated Easter on 22 March (Mosshammer 2008). If Cyril used the tables (Neugebauer 1979) then the Alexandrian Easter full Moon was on 21 March (Saturday) and Alexandria could have celebrated Easter on 22 March as well. This could have been truly a happy accident 20 March was a forbidden day for the Easter full Moon in the Alexandrian calendar, so that Alexandrians could grumble over Roman computus although they were likely to have been satisfied with the result. Still, such an event could have rung alarm bells in Alexandrian society, leading Hypatia to investigate the cause of the problem. It is likely that she would have done so at the instigation of the Prefect of the city hence the observation that she had frequent interviews with Orestes. Though Easters in years 415 (11 April ) and 416 (2 April) were far from the equinox and not subject to any controversy, her investigations and a report to the prefect in 415 could have led to further alarm in the city, and her conclusions in 416 could have been the last straw. Religious riots in Alexandria c. 417 The most important (if not the only) source on the 417 Christian-Jewish clash in Alexandria, again, is Socrates (ch. 13). He gives no precise time, but the order of his narration seems to place the first riot some time between Cyril s rise to bishop (412) and the murder of Hypatia. There is an astronomical link between Easter and Passover dates. Passover was supposed to fall on the first spring full Moon; the Easter full Moon is a direct Christian analogue. Hence the Christian Jewish violence in Alexandria around the time of Hypatia s murder could have had the same cause: in 417 the Jewish Passover was going to fall on 17 March, in agreement with the Roman Easter full Moon. On reading Socrates, Bright (1860) went so far as to summarize the situation as follows: Had there been no onslaught on the synagogues, there would doubtless have been no murder of Hypatia. While this seems merely a wild guess, let us develop the idea. First, I argue that the Roman church and the Jews fixed both the full Moon and Passover on the same date, 17 March. In my opinion, this coincidence with the Roman dates could have been understood as both real and unfortunate by Alexandrian clergy. This could have been the true reason for the violence against Alexandrian Jews. In 417, Alexandrian Jews celebrated Passover on 17 March, or at least they intended to celebrate it on that date, according to evidence from the date of composition of a Ketuba (marriage contract) from another Egyptian city, Antinoopolis (Stern 2001). A letter from Paschasinus, a bishop of the city Lilybæum, Sicily, to Pope Leo the Great, written on the eve of the controversial Easter of 444, mentions Easter 417: In the 11th consulate of Honorius Augustus and the second of Constantius, to avoid having Pascha on April 2.12 A&G April 2010 Vol. 51

5 22, they [Romans] celebrated it on March 25. The 11th consulate of Honorius Augustus and the second of Constantius was in 417. For the Roman Easter to fall on 25 March with Luna XXII (Krusch 1880, Mosshammer 2008) means that the Roman Easter full Moon had to fall on 17 March. Paschasinus further says that Alexandrians still celebrated it in April and, further, tells a miracle story that confirmed 22 April as the correct day for Easter. Some years later, the echo of that controversy was heard in a letter by Alexandrian Bishop Proterius, on the eve of another controversial Easter, in 455 (Krusch 1880). The following passage is the most conspicuous: But some, ignorant of the subtlety of the computus, have been misled by Jewish lies into thinking that we celebrate in the second month when we extend Easter so far The Jews are as ignorant of the Pasch as they are of God. They often go back of the first month and observe the Passover in the twelfth (Krusch 1880, Jones 1943). The phrase some, ignorant of the subtlety of the computus in this context could refer only to the Romans, or rather, to the Pope himself. The problem that Proterius identifies with Jewish lies is that of celebrating Easter in the second month rather than in the first, in other words that the Alexandrian equinox is misplaced so that Easter is celebrated too late in the year. The words chosen by Proterius reveal anger and a barely hidden threat. Such anger suggests some sort of long-term problem, perhaps that this correlation between the Roman and the Jewish calendars on several occasions had provoked an entrenched suspicion among Alexandrian clergy in the fifth century. If so, the Alexandrian church, and probably Bishop Cyril, could have perceived a conspiracy behind the stand of Hypatia Orestes, Rome and the Alexandrian Jews, over these dates. Because the Alexandrian church was not powerful enough to harm Rome directly, they provoked attacks on the two other components and the Prefect, a representative of the Empire at large. Conclusion I have presented an original reconstruction of what might have happened in Alexandria around 417. Being unaware of atmospheric refraction, Hypatia could have misjudged the time of the vernal equinox, placing it at least two days early and at least four days earlier than the date reckoned by the Alexandrian church. Her seemingly simple logic threatened the supremacy of the Alexandrian church over the date of Easter, because it led to the same date as the Roman calculation. As a consequence, the Alexandrian Christian zealots following Bishop Cyril killed her. Suspecting the Jewish community to be in conspiracy with Rome over the choice of the Easter full Moon in 417, the 2: Rachel Weisz as Hypatia and Michael Lonsdale as her father Theon in Sony Pictures 2009 film Agora. Set in AD 391 in Roman Egypt, the story focuses on a slave who turns to the rising tide of Christianity in the hope of pursuing freedom while also falling in love with his master, the famous female philosophy professor and atheist Hypatia of Alexandria. (Newmarket Films) Christian mob attacked the Alexandrian Jewish community as well. Hypatia must be credited for going beyond the stifling boundaries of Ptolemy s Syntaxis. But she certainly overstretched her authority in observational astronomy. While calendar rivalry in the ancient time always led to the most violent clashes, the status of Ptolemy s Syntaxis as the astronomical authority in Alexandria, greatly contributed to this effect. The conjectures outlined here offer questions about the state of astronomy and quality of clocks in fifth-century Alexandria. A historical note is also of relevance. Year 2010 is separated from 414 by 1596 years, exactly three 532-year (Dionysian) cycles. Incidentally, it is also eighty-four 19-year (Alexandrian) cycles and nineteen 84-year (Roman) cycles. Therefore all calendar events related to Easter in 416, including Lent, riot, murder and so on will fall on the same weekdays and dates in This is the first such occasion since 416. Therefore it will be fair to commemorate Hypatia s death in the year 2012, on 21 March, according to the Julian calendar, or on 22 March, according to the Gregorian calendar (the proleptic Gregorian calendar was only one day behind the Julian in the fifth century). Ari Belenkiy, Bar-Ilan University, Israel. Acknowledgments. Thanks to Reinhold Bien (Heidelberg), Joan Griffith (Annapolis, MD), Axel Harvey (Montreal), Larry Horwitz (Tel-Aviv), Jan Kalivoda (Prague), Yaqov Loewinger (Tel-Aviv), Philipp Nothaft (Munich), Tom Peters (Amsterdam), Giancarlo Truffa (Milan), Eduardo Vila-Echagüe (Santiago, Chile) and Yaakov Zik (Haifa). 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