In a similar way, but by no means equal in size or power, next to it is the star Mercury, by some called Apollo; it is carried on a lower circle and is quicker by nine days, shining sometimes before the rising of the sun, sometimes after its setting, but never further from it than 22°, as Kidinnu and Sosigenes say.(Kidinnu is one of the few Babylonian astronomers whose names we know) and again (ibid. 18.82):2
There have been three schools of astronomy, the Chaldean [Babylonian], the Egyptian, and the Greek. To these, the Dictator Caesar added a fourth amongst us, regulating each year according to the course of the sun, recruiting Sosigenes by reason of his skill in this science.From these two passages we can glean that Sosigenes was an astronomer of note and presumably a rough contemporary of Julius Caesar, enabling us to tentatively assign dates of c. 100 BCE to c. 30 BCE.
The main point here is that Sosigenes was the main technical architect of the Julian Calendar. He would have known that 365 + 1/4 days was a reasonably good and simple approximation for the length of the tropical year, since this had been established from at least the time of Kallipos around 350 BCE. He must have been aware too of the work of Hipparchos two centuries later showing that better values were available, such as 365 + 1/4 – 1/300 days. However, it is likely that, charged with putting in place a simple and workable scheme to replace the existing and chaotic Roman Calendar, he chose the long established approximation. No doubt he was guided by the fact that such a calendar had already been proposed for Alexandria in 238 BCE (possibly by Eratosthenes) under the auspices of King Ptolemy III Euergetes but it was never implemented. This proposal was simply to add an extra day every fourth year.
Sosigenes evidently chose to do the same, but that was the easy, theoretical part. The Egyptian Calendar, with its simple system of 12 months of 30 days, plus 5 epagomenal days at the end of the year, was straightforward to modify by adding another epagomenal day. However, the Roman Calendar, with its irregular months of 23, 24, 29 or 31 days was a mess, as was the calculation of how many days had been missed out over the previous decades (around 80 in fact). Thus, the main part of Sosigenes' efforts would have been to unpick the existing calendar and to devise a means of fixing it that incorporated the established principles of the calendar that were acceptable to Romans. The problems surrounding calendar reform were thus largely those of implementation, not astronomy.
It seems obvious that the best way to do this would have been for Sosigenes to come to Rome in order to discuss matters directly with the College of Pontiffs (Collegium Pontificum), the priests who administered the Roman calendar and who declared intercalary days and months. As a native of Alexandria, which had its own long established Egyptian Calendar, Sosigenes may not have known much about the Roman Calendar which was by comparison very idiosyncratic and (paradoxically) provincial. The College of Pontiffs, charged with regulating the religious rites of the Roman state, actually wielded a lot of power behind the scenes, and their ability to determine intercalations was often used to further political or commercial objectives through bribery, as the late C4th CE historian Ammianus states (26.1.12).
.jpg) |
The Tusculum bust of Julius Caesar in the Turin
Archaeological Museum. Image: Wikimedia Commons.
|
However, we know from Pliny and other writers, such as Solinus (early C3rd CE) and Macrobius (early C5th BCE), that it did not go well. Pliny goes on to say (ibid. 18.82):3
Also, the calculation itself, upon the discovery of an error has been corrected in this way: by making no intercalations for twelve successive years, since the year which previously anticipated the stars, was now beginning to fall behind. However, even Sosigenes himself, though more correct than others, has not ceased to have his doubts by his continual corrections in three separate books.This is somewhat mysterious, insofar as Pliny does not reveal exactly what went wrong, but it does point to the continued involvement of Sosigenes with the project, at least on a theoretical level. Ammianus (26.1.8–14) tells us that the final implementation was due to Augustus but nothing of the preceding problems. Fortunately, Macrobius (Saturnalia 1.14.13–15) to some extent at least lifts the veil on the mystery:6
And so, with the calculations established, Caesar published by public edict the monthly structure of the civil year, and the arrangement might have continued to stand had not the correction itself of the calendar led the priests to introduce a new error of their own; for they proceeded to insert the intercalary day, which represented the four quarter-days, at the beginning of each fourth year instead of at its end, although the intercalation ought to have been made at the end of each fourth year and before the beginning of the fifth. This error continued for thirty-six years by which time twelve intercalary days had been inserted instead of the number actually due, namely nine. But when this error was at length recognised, it too was corrected, by an order of Augustus, that twelve years should be allowed to pass without an intercalary day, since the sequence of twelve such years would account for the three days which, in the course of thirty-six years, had been introduced by the premature actions of the priests. After this, he ordered that one day, according to the ordinance of Caesar, be intercalated at the beginning of the fifth year also, and mandated the whole scheme for observation in perpetuity by the engraving of a bronze tablet.So, for 36 years the February leap day had been added every three years instead of every four, resulting in a calendar that was in advance of the actual tropical year by three days. How did this actually go wrong in practice?
We know from Varro (The Latin Language 6.13)7, who was writing around 50 – 45 BCE, that the traditional last day of the year in the Roman Calendar was the last day of February, the festival of Terminalia. The previous year (46 BCE), it will be recalled, had 445 days, so that 45 BCE (now starting on 1st January under the new system) was already synchronised with the Sun. The plan was to insert the new leap day on 29th February 41 BCE in four years time and every four years thereafter. However, Julius Caesar was assassinated on 15th March 44 BCE and thus was not able to oversee the correct implementation of the new scheme.
Whether by incompetence or intent, what actually happened was that the College of Pontiffs inserted the first leap day on 29th February 42 BCE, a year too early. Perhaps there was confusion over what 'every four years' meant in practice. The common ancient method of counting, particularly with dates, was to count inclusively instead of the mathematically correct, exclusive method. So that, for example, the difference between 5 and 8 would be given as 4. Carrying on in this way, the pontiffs set the next leap year as 39 BCE instead of 37 BCE, then 36 BCE instead of 33 BCE, and so on.
It was not until 9 BCE, when 36 years had passed from the initial introduction of the Julian Calendar, that the error was realised. Under the direction of Augustus Caesar, who was also Pontifex Maximus, twelve years were then allowed to pass without leap days, in order that the error of three days could be corrected without undue reorganisation. Therefore, by 4 CE, the calendar was back on track again, and the first leap year after that date was correctly set as 8 CE.
Unfortunately, we do not know how the mistake was uncovered in 9 BCE. It seems unlikely that anyone would have noticed an actual discrepancy of just three days with regard to the seasons. It must have been due to some kind of expert review into the calculation. Was it, as Pliny suggests, because Sosigenes has continued to follow developments and written about them or was it due to some other cause? If Sosigenes was actively involved, surely the error would have been corrected much sooner, perhaps by 38 BCE? On the other hand, unless he were exceptionally young when first consulted by Caesar around 47 BCE, it seems unlikely that he would still have been alive in 9 BCE.
In sum, the evidence suggests that we can credit Sosigenes with the fundamental design of the Julian Calendar, but in accomplishing this he was not really doing anything that was new to the world of astronomy. What we do not know is to what extent he was involved with the nitty-gritty of the changes that were made to the old Roman Calendar and whether he was responsible, either directly or indirectly through his writings, for sorting out the bungled implementation.
Lunar Crater: Sosigenes (diameter 17 km).
NOTES
1. simili ratione, sed nequaquam magnitudine aut vi, proximum illi mercurii sidus, a quibusdam appellatum apollinis, inferiore circulo fertur viiii diebus ociore ambitu, modo ante solis exortum, modo post occasum splendens, numquam ab eo xxii partibus remotior, ut cidenas et sosigenes docent. ideo et peculiaris horum siderum ratio est neque communis cum supra dictis. nam ea et quarta parte caeli a sole abesse et tertia, et adversa soli saepe cernuntur, maioresque alios habent cuncta plenae conversionis ambitus in magni anni ratione dicendos.
2. Tres autem fuere sectae, Chaldaea, Ægyptia, Graeca. His addidit quartam apud nos Caesar dictator annos ad solis cursum redigens singulos Sosigene perito scientiae eius adhibito.
3. Et ea ipsa ratio postea conperto errore correcta est ita, ut duodecim annis continuis non intercalaretur, quia coeperat ad sidera annus morari, qui prius antecedebat. Et Sosigenes ipse trinis commentationibus - quamquam diligentior ceteris, non cessavit tamen addubitare ipse semet corrigendo.
4. Conversus hinc ad ordinandum rei publice statum fastos correxit iam pridem vitio pontificum per intercalandi licentiam adeo turbatos, ut neque messium feriae aestate neque vindemiarum autumno conpeterent; annumque ad cursum solis accommodavit, ut trecentorum sexaginta quinque dierum esset et intercalario mense sublato unus dies quarto quoque anno intercalaretur. Quo autem magis in posterum ex Kalendis Ianuariis novis temporum ratio congrueret, inter Novembrem ac Decembrem mensem interiecit duos alios; fuitque is annus, quo haec constituebantur, quindecim mensium cum intercalario, qui ex consuetudine in eum annum inciderat.
Then turning his attention to the reorganisation of the state, he reformed the calendar, which the negligence of the pontiffs had long since so disordered, through their privilege of adding months or days at pleasure, that the harvest festivals did not come in summer nor those of the vintage in the autumn; and he adjusted the year to the sun's course by making it consist of three hundred and sixty-five days, abolishing the intercalary month, and adding one day every fourth year. Furthermore, that the correct reckoning of seasons might begin with the next Kalends of January, he inserted two other months between those of November and December; hence the year in which these arrangements were made was one of fifteen months, including the intercalary month, which belonged to that year according to the former custom.
5. adeo aberratum est, ut C. Caesar pontifex maximus suo III et M. Aemilii Lepidi consulatu, quo retro delictum corrigeret, duos menses intercalarios dierum LXVII in mensem Novembrem et Decembrem interponeret, cum iam mense Februario dies III et XX intercalasset, faceretque eum annum dierum CCCCXLV, simul providens in futurum, ne iterum erraretur: nam intercalario mense sublato annum civilem ad solis cursum formavit. Itaque diebus CCCLV addidit decem, quos per septem menses, qui dies undetricenos habebant, ita discriberet, ut Januario et Sextili et Decembri bini accederent, ceteris singuli; eosque dies extremis partibus mensium adposuit, ne scilicet religiones sui cuiusque mensis a loco summoverentur. Quapropter nunc cum in septem mensibus dies singuli et triceni sint, quattuor tamen illi ita primitus instituti eo dinoscuntur, quod nonas habent septimanas, ceteri tres omnes alii reliqui quintanas. Praeterea pro quadrante diei, qui annum verum suppleturus videbatur, instituit, ut peracto quadrienni circuitu dies unus, ubi mensis quondam solebat, post Terminalia intercalaretur, quod nunc bis sextum vocatur.
The confusion was such that Caius (Julius) Cæsar, sovereign-pontiff, resolved in his third consulate and that of M. Emilius Lepidus to destroy the effects of past abuses by placing between the months of November and December, two intercalary months of 67 days, although he had already intercalated 23 days in the month of February, which gave 445 days to that year; and at the same time to prevent the return of similar errors, he suppressed the intercalary month, and established the civil year after the course of the sun. Hence to the ancient 355 days of Numa’s year he added ten days, which he divided among the seven “short” months of 29 days, in such a manner that two days were added to January, August and December and one to the other months; and he placed these supplementary days at the ends of the months, so as not to disturb the religious festivals. It is for this reason that today, although we have seven months of 31 days; yet there are only four which have retained the following peculiarity of the ancient system: that the Nones fall on the seventh day, while in the others it falls on the fifth. And to take account of the quarter of a day which it seems completes the solar year, Cæsar ordered that after each revolution of four years, there should be added, after Terminalia, instead of the ancient month, an intercalary day, which is now called leap-year day.
6. Sic annum civilem Caesar habitis ad lunam dimensionibus constitutum edicto palam posito publicavit. Et error hucusque stare potuisset, ni sacerdotes sibi errorem novum ex ipsa emendatione fecissent. Nam cum oporteret diem qui ex quadrantibus confit quarto quoque anno confecto, antequam quintus inciperet, intercalare: illi quarto non peracto sed incipiente intercalabant. Hic error sex et triginta annis permansit: quibus annis intercalati sunt dies duodecim, cum debuerint intercalari novem. Sed hunc quoque errorem sero deprehensum correxit Augustus, qui anno s duodecim sine intercalari die transigi iussit, ut illi tres dies qui per annos triginta et sex vitio sacerdotalis festinationis excreverant sequentibus annis duodecim nullo die intercalato devorarentur. Post hoc unum diem secundum ordinationem Caesaris quinto quoque incipiente anno intercalari iussit, et omnem hunc ordinem aereae tabulae ad aeternam custodiam incisione mandavit.
7. Terminalia, quod is dies anni extremus constitutus: duodecimus enim mensis fuit Februarius et cum intercalatur inferiores quinque dies duodecimo demuntur mense.
The Terminalia [Festival of Terminus[, because this day is set as the last day of the year: for the twelfth month was February, and when the extra month is inserted the last five days are taken off the twelfth month.
Last updated 08/06/20
No comments:
Post a Comment