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Computerised Resources for Historical Research: Calendars, Chronology and the Life of Jesus Christ

Alexandra SmithCardiff University

AbstrAct

The calendars of ancient and medieval Europe were based on astronomical observa-tions, and although the Julian calendar, the primary calendar of the Middle Ages, was divorced from the phases of the Moon, observations of the celestial sphere still formed the basis for setting the moveable Christian feasts. When establishing chronological sequences, historians do not always find the relevant calendrical dates in the sources, and are forced to look to details such as the timing of the phases of the Moons, or dates of eclipses, to establish a chronology. Despite recent advances in computing, in-cluding the development of a variety of programs to compute astronomical events that are relatively easy for non-astronomers to use, many scholars still turn to out of date information, such as the three volumes of F.K. Ginzel’s Handbuch der Mathematischen und Technischen Chronologie, dating between 1906 and 1914. This chapter presents in-formation needed to understand these calendars, and the computerised tools available to manipulate the data. As an example of the information and resources available, the author examines the evidence for the lifetime of Jesus Christ, which includes a mysteri-ous star, two lunar eclipses, a solar eclipse and historical evidence. It demonstrates some of the tools available currently and emphasises the value of using the historical sources in conjunction with up-to-date astronomical data.

The computer has brought many significant changes to the way in which we commu-nicate and conduct research. The impact of the most widely available computerised tools on the scholarly community cannot be underestimated, with word processing, spreadsheets and databases providing the format for a great deal of research, as well as platforms for the storage and manipulation of data. Additionally, the internet provides access to a wealth of information that might otherwise have been difficult or impossible to obtain, and allows swift communication between scholars as well as discussion and the dissemination of results through online publications, websites, portals, sites such

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as Wikipedia (www.wikipedia.org), and weblogs1. Through podcasts and webcams we are able to hear an argument as it is presented, without being present ourselves. In addi-tion to this, computers provide a platform for the development of specialised software which can be used in different disciplines, from the modelling of the complexities of the Earth’s atmosphere to the development of special tools to convert ancient Greek Unicode script into universal code. In the last thirty years things have progressed at a dramatic rate, and in so many ways that no single individual could hope to keep track of the developments in all fields.

In this chapter I will examine the impact of computers and computerised resources on research into calendrical issues. Currently there are a wide range of resources available to those conducting research in this field, which by necessity bring the scholar into contact with astronomical computations, since all calendars have astronomical obser-vations or calculations at their core. While the number, availability and usability of these tools has improved a great deal in recent years, there does not seem to have been a commensurate increase in awareness of their existence and potential use in historical research, and many scholars still consult outdated astronomical information from the late 19th century. Additionally, in raising awareness to the available resources, I also feel it important to emphasise the uncertainties inherent in astronomical data, which are not generally apparent. The chapter will conclude with a case study – examining the historical evidence for the chronology of Jesus Christ – which will illustrate the use of some of the resources available, discussing their strengths and weaknesses.

cAlendArs And religion

Every society has a calendar by which it reckons the passage of days and years. Because there are so many societies, and so many different calendars, by necessity this discus-sion is confined to the ancient Mediterranean, Israel and the medieval period in Eu-rope. These calendars are interconnected in terms of development and maintenance, but for all their similarities there is also a great deal of difference, and complexity. All of these calendars originated from astronomical observations of the movements of the heavens, and all had a religious connection, being developed or maintained by religious authorities within society, who regulated the religious cycles and festivals on behalf of the people.

The simplest European calendar is that which follows the agricultural cycle, perceiving time as the passage of the seasons and associated tasks. The earliest written evidence for such a calendar comes from Hesiod in late 8th century BC Greece, whose poem Works and Days describes how to watch the heavens for the rising and setting of certain stars and to pay attention to natural cycles, such as the migration of birds, in order to know which agricultural tasks should be started or finished. For example, the flight

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of the crane indicates the time for ploughing, and when the star Arcturus first rises in the evening it is best to start pruning vines2. The use and value of such a cycle persisted throughout history, even alongside more systematic means of reckoning time. The Ro-mans, for example, added a great deal of folklore to the Greek body of knowledge, and in the medieval period we see the cycle represented as the Labours of the Months in books, mosaics, paintings and even stained glass windows3. These medieval depictions usually show the astrological sign alongside an agricultural task, such as ploughing or reaping, which shows that the pertinent information for the agricultural population, and therefore the majority of people, was encapsulated in the rhythms of nature.

Hesiod also indicates the existence and use of a civil calendar with named months, which he considers primarily as a framework for those days which are designated as sacred or profane. For example, the last day of the month is sacred to Zeus and the best day to oversee work, while the fifth is always a bad day, and the second is neutral4. This presumably reflects the calendar of Ascra, where Hesiod lived, and would not have been universal. At this time, and until the Hellenistic period, each city-state of Greece had its own calendar, with its own months, patron deities, festivals and holidays, and methods for maintaining it with the year. Although these calendars were primarily re-ligious in nature, they were also important for the calculation of secular activities, such as the interest on loans and appropriate days for political activity.

Due to the uneven survival of the evidence, the only ancient Greek calendar we know well is that of Athens. Athens had two calendrical systems running concurrently, form-ing a single calendar. The first system was the festival calendar, which followed a com-mon calendrical pattern: there were 12 months in a year, and each month started at the new moon. It was intended as an observational calendar, so the month would start the morning after the new lunar crescent was first sighted, and would run for 29 or 30 days, depending on when the new moon of the subsequent month was sighted. A 12-month lunar calendar only has 354 days in it, and the solar year is approximately 365.25 days long, so the new year of a lunar calendar will gradually slip with respect to the seasons, moving 11 or 12 days back through the year annually. The testimony of Plato (428-347 BC) suggests to us that from the 4th century BC the Athenian calendar year started with the first new moon after the summer solstice, but prior to this the evidence is not sufficient to build up a reliable picture5. In order to keep the calendar approximate-ly aligned with the seasons, they would add in an extra month, called an intercalary month, every few years. It is difficult to see whether they intercalated irregularly, or according to some fixed scheme, until the 4th century BC when they appear to have be-gun to use the Metonic cycle, which intercalates seven months into every 19 years. This cycle was actually a development of Babylonian astronomy and passed to the Greeks in the 5th century BC6. The individual responsible for the maintenance of the festival calendar was the archon for the year – an annually elected eponymous magistrate who, while not a priest himself, had a number of duties relating to the festivals and rituals of

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Athens. The second aspect of the Athenian calendar was the consiliar, or prytany, calen-dar, which governed the meetings of the Athenian legislative body, the boule [council]. Following the reforms of Cleisthenes in the late 6th century BC, the Athenians were divided into ten tribes, and each political year was divided into ten parts, or prytanies; each tribe presided as chair for the rest of the boule for the duration of one of these divisions, in a role also called a prytany. In the 5th century BC, the prytany year had 365 days, with each tribe serving for 37 or 36 days, but from ca. 407 BC, these were reduced by a day in order for the two calendrical systems to be synchronised7. It seems that prior to this there may have been some disruption to the festival calendar, which upset the Athenians because it was of great importance that the gods were honoured on the correct feast days8.

Although we do not have much information about other states, and certainly nothing to rival our understanding of Athens, it appears that most states had something similar in operation to the Athenian festival calendar. Because they intercalated months differ-ently, celebrated and emphasised different festivals, had different criteria for the new year, and the start of each month relied on observations of the new moon that could vary from one place to another by several days, the different state calendars were never synchronised. It is this confusion that caused the 5th century historian Thucydides to abandon calendrical reckoning for his History of the Peloponnesian War, and divide the year into summer and winter.

The Jewish calendar is also based on the cycles of the moon, with 12 months to a year. It has undergone a number of changes during its existence, including the month names and intercalation methods. Initially months appear to have been intercalated irregular-ly, based on seasonal and agricultural conditions, and by the 6th century AD there were a number of different versions of the calendar; eventually, however, the 19-year Me-tonic cycle was adopted, possibly as early as the 4th century AD. The new year begins around the time of the vernal equinox, and the calendar was originally observational, based on sightings of the new moon’s crescent. However, at some point from the 4th century AD, this was replaced by calculations of the conjunction of the Sun and Moon (a conjunction occurs when there is only a small angle separating two astronomical objects on a line of sight). Decisions regarding the calendar were made by a small sub-committee of the Sanhedrin, whose role was to verify the beginning of the new month and decide whether a month should be intercalated. The calendar governed all aspects of Jewish life, including fixed feast days, liturgical days and mobile festivals. The Jewish day is considered to start at sunset, but this was not always the case as the older texts, such as the Old Testament, include examples of the day starting at dawn; however, from the 1st century AD all references to this cease. The calendar of the Jews was strongly in-fluenced by the Babylonians, and still has Babylonian-inspired month names; although during the Roman period the Jews adopted the Roman calendar for their civil dealings,

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their own calendar remained for religious observances, and they considered this their primary means of tracking time9.

In its earliest known phases, the Roman calendar also followed a 12-month cycle with an extra month intercalated, but from the 5th century BC the month lengths were fixed so that the year was 355 days long, with 22 or 23 days inserted into Februarius every other year. Just like the Greeks, the Romans had days designated as sacred and profane, as well as specific dates for festivals. However, they had but one calendrical system, maintained by the Pontifex Maximus, the high priest of the College of Pontiffs. This office was generally held by the elite, who had access to all the political offices, and was therefore subject to political influence; since the timing of the months affected political issues such as the timing of elections, intercalation became politicised and there was a certain degree of tampering with the calendar. Thus, from time to time, it became woe-fully misaligned from the seasons, the most notable occasion being in the 2nd century BC, where it was as much as four months ahead10. These problems prompted Julius Caesar to reform the calendar, and from 45 BC the fixed month lengths were changed so that the year had 365 days, and a leap day was added into Februarius every four years. This is ostensibly the same calendar that endured through the Middle Ages and was re-formed by Pope Gregory XIII in AD 1582, although it underwent minor revisions un-der Augustus. Caesar’s changes to the calendar caused confusion, especially with regard to the dates of festivals and anniversaries, which were exacerbated because the Romans counted some of their days backwards from the start of the next month. This meant that dates that had previously been, say, ten days before the end of the month were now a different date because the month had more days; people were forced to make a deci-sion about how they perceived such days. The Romans had a strong affinity for anniver-saries, perceiving what we would see as the same date separated by a number of years as being the same actual day, so this must have been a significant decision for many11. After the calendar reform, the responsibility for maintaining it remained with the Pontifex Maximus, and in the medieval period passed to the Pope and the Church12.

In the later Roman Empire, probably under Diocletian, a new calendrical cycle was introduced to run concurrently with the Julian calendar: the indiction. This was a 15-year cycle commencing from 1 September, and was entirely secular, designed to govern tax collection and the payment of wages. The years within an indiction were numbered, but the individual indictions themselves were not because they were never intended as a tool of chronology, only for fiscal purposes.

The medieval European civil calendar was simply an extension of the Julian calendar, maintained by the Pope and using the same months and leap years, but there were several different, concurrent calendrical systems in place, with a great deal of regional variation. For example, the start of the year could be any one of several dates including 1 January, 1 March, Easter, 25 September or 25 December. There were also several dif-ferent eras in effect, including the era of the reigning Pope or king, the Era of Spain, Era

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Diocletian, the foundation of Rome, and dating from the Annunciation. The calendar was full of feast days, but these could vary in date and significance between nations, so there was no sense of a unified European calendar. The indiction cycles continued through the medieval period, having been co-opted by scribes and chronologers to date events and documents. The common people seem to have used feast days as convenient ways to reckon time and note key points during the year. For example, the start of sum-mer was St. Urban’s day rather than 25 May, and the spring rents in England were due on Hocktide, the Monday and Tuesday in the utas, or octave, after Easter. Although the Catholic Church and states of Europe were separate, there was one calendar for all Christians13.

The most complicated calendrical cycle in the Middle Ages was the Easter calculation cycle, called the computus. This was based on the Jewish calendar, as the first Easter fell one or two days after Passover, but Christians celebrate Easter on the first Sunday after the fourteenth day of the moon, after the vernal equinox. This means that Easter is a moveable feast, dictating the timing of a number of other mobile feasts through the year. Fixing the date of Easter was a significant problem in the early medieval period, causing a number of disputes, and was addressed by monks such as Dionysius Exiguus (AD ca. 470 – ca. 544), and Bede (AD ca. 672-735). The ultimate solution lay in the same 19-year lunar cycle (Metonic cycle) as employed in the Jewish calendar, which means that the dates of Easter recur every 19 years. The method of computation in-volved is mathematically complex, and the required level of numeracy was not wide-spread in the Middle Ages.

Easter is one example of many religious observances that relied specifically on an astro-nomical event for their timing; some of these fell at the same time annually, others were moveable. For example, the last day of the Greek Olympic Festival coincided with a full moon, as did the original Roman festival of Anna Perenna (before the months were fixed)14. The calendar date of such festivals would have varied slightly from year to year within each state’s calendar, depending on the timing of the sighting of the lunar cres-cent and intercalations. It would also have varied with respect to the solar year (i.e. the date given by our own calendar) because the full moon would not fall on the same date each year. Festivals that drew attendance from a variety of people from different places, like the Olympics or Easter, were difficult to co-ordinate when those involved each used a different set of months, days or years. Therefore it was essential to have a fixed point in the year to refer to, and astronomical events would have been the most reliable. So Easter took the vernal equinox as its marker, while the Olympics used the midsum-mer solstice, and the First Fruits festival at Delphi used the rising of Delphinius15. If an event is dated with respect to a fixed feast date, then with an understanding of the relevant calendar, it is relatively straightforward for us to establish a calendrical date for it; but if that event is dated with respect to a moveable feast, then an understanding of the astronomy underlying the observation for the festival is also important.

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The connection between religion, astronomy and calendar is apparent, and for most societies, control of the calendar fell to those with religious power and influence: the Pontifex Maximus or the Sanhedrin, for example. Athens is a something of an excep-tion, having delegated the responsibility for the festival calendar to the archon, who had religious authority but was not a priest himself. The connection between the calen-dar and faith has been broken in modern times, such as in England, where St. George’s day is not a public holiday, but in antiquity there was less delineation between religious and secular activity. For example, in ancient Greece, political activity was not permit-ted on festival days, in the Jewish calendar most activities cannot be performed on the Sabbath, and the Romans had dies nefasti, on which no public vote or legal action could be taken.

That the calendar was almost exclusively presided over by religious bodies probably stems from the relationship between the celestial bodies and the gods. In most faiths the gods themselves, or their wishes, were represented in the heavens, leading to the development of astrology. For a long time, theological reasoning governed man’s un-derstanding of the heavens, and the belief that whoever created the world would have placed the Earth at the centre of the universe was prevalent until the time of Coperni-cus (1473-1543), and arguing against it saw Galileo (1564-1642) accused of heresy. If a society uses the heavens to determine the time of year, and consolidates that informa-tion into a structure that can then dictate the timing of events, the logical choice of per-son to oversee that is someone with insight into the heavens, i.e. a religious figure. Once the connection between the gods and the calendar is established, there is no reason to change it, for only a priest would be able to interpret the signs and thereby know when to place the feast days in order to best please the gods. Civil considerations, such as the determination of interest at the end of the Greek month, were later developments added to the calendar as an adjunct to the religious element.

To control time is to control a society, and there are examples from each of the societies discussed to show that where the calendar’s workings were coveted information, the common people did not appreciate the power held over them. The Romans, for ex-ample, had their calendar made public in the 4th century BC when, following a public outcry, Gnaeus Flavius stole and published the calendrical tables for all to see16. This undermined the authority of the patrician class, who monopolised the highest politi-cal and religious offices, even though the plebeian class was eligible to perform them. People wanted to feel that they were in control, and the calendar was representative of that. Although in actuality the people had no control over the calendar after its publica-tion, being able to observe its variations for themselves gave them a sense of ownership, and this was coupled with greater access to political power, which, by its exclusivity, was symbolised by the calendar. In the medieval period, the calendar was widely published as Books of Days, which were reusable year after year. This put time in the public do-main, and was emphasised further by the appearance of church clocks – but the extent

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to which people had control over time was just as limited as ever. The Books of Days also included information that would permit those with the requisite numeracy to cal-culate the date of Easter, again increasing the feeling of inclusion and involvement in the calendar, but most people would not have been able to afford a Book of Days, most would not have been able to read it, and of those who could, very few would have been able to calculate Easter from them. Their purpose was to give people the sense of being part of something, while simultaneously reinforcing the position and authority of the established hierarchy. Although no power was granted to the people to influence the calendar, they felt like they were a part of it.

Thus the calendar was also a means through which a society was able to express its iden-tity, and this is the reason for each Greek city-state having its own calendar. In order for one state to differentiate itself from its neighbours, and develop communal ties between different members of its society, it develops a number of institutions. The role of the cal-endar is to provide a temporal framework within which all members of the society can operate, and therefore conduct religious observances and political activities at the same time, even when they cannot be in the same place. This brings a sense of community through shared experience. In addition to this, having certain festivals and times of the year particular to a given community creates a bond between the people within it, and a sense of difference from others. Foreigners and slaves might be excluded from some festivals in order to emphasise this perception of belonging. The calendar can go fur-ther, though, into being directly representative of the identity of the society itself; there is evidence that the Jewish calendar, for example, lost its solar element during the 1st century AD, emphasising its lunar aspects, which S. Stern interprets as an expression of Jewish identity in the face of the Roman occupation of Judea17. It was important for the Jews to emphasise their difference, and maintain a distinct identity at a time when their culture was under attack. Conversely, Roman culture was very inclusive, absorbing the festivals of the societies they controlled into their own calendar. This was part of the process by which the Romans were able to govern societies outside their own, because they included them in their way of life, including the calendar, rather than imposing their own culture. The calendar was a part of the process of making people feel like they belonged, and it is presumably this very process which the Jews were deliberately avoid-ing. The Romans were able to maintain a sense of identity in the face of these changes through the continuing practice of older traditions, and an emphasis on the antiquity of their society and rituals. Although they gained new feast days and ceremonies, they did not replace the old ones.

In the later Roman Empire, once Christianity became the canonical religion, Christian festivals came to overlay existing pagan festivals in a similar manner to the way in which the Romans had absorbed the religions of others18. In addition, because the Christian faith adopted the Old Testament, it also inherited a number of the Jewish festivals. In order to maintain its own identity without losing its heritage, those dates remained the

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same but the festivals changed. For example, the Jewish liturgical day for the Glorifica-tion of Moses became the Transfiguration, while the nature of Pentecost changed from the restrictive Jewish holiday to a celebratory Christian one19. Religion and identity are strongly connected, and the calendar is an expression of this connection.

cAlendArs, chronology And computers

In addition to the astronomical basis for the calendars of historic Europe, a number of historical events, including battles, births and deaths, are connected with more unique astronomical events. Examples include the lunar eclipse before the battle of Pydna in 168 BC and the comet that was seen as heralding the death of Alfred the Great in AD 891, and events such as these can provide dates in addition to direct calendrical infor-mation20. Before the development of computers, tasks such as the determination of the first new moon after the summer solstice – the supposed start of the Athenian calendar year from the 4th century BC – had to be calculated by hand, but with computer mod-elling and programming we can get more accurate and rapid results. A brief overview of the complexities of the astronomical information and the problems inherent such calculations follows, as well as a discussion of the value of some of the resources cur-rently available.

The moon is the most fundamental object that we need to understand in order to inter-pret material that includes lunar month dates or solar and lunar eclipses. Unfortunately, the moon is incredibly complex in its movements, as it is perturbed by the gravitational fields of the sun, Earth and the other planets, and its apparent position in the sky is affected by the speed of the Earth’s rotation, which is variable and decreasing at an ir-regular pace. The equations governing its motion have ten times as many terms as those governing the motion of the sun, which means that during the ancient and medieval pe-riods computing the moon’s path accurately was nigh impossible. Thus, when Edmund Halley (1656-1742) tried to calculate the position of the moon in AD 1693 from the 2nd century AD tables of Claudius Ptolemy, he found that the moon was in advance of his calculated position21. Scholars attempted to account for this by employing ancient eclipse data, which give precise positions in the sky for the sun and moon at a particular moment, and this research culminated in the late 19th century eclipse canons of T.R. von Oppolzer (1887) and F.K. Ginzel (1899)22. These calculations were performed by hand, taking many painstaking hours, and were repeated in subsequent decades with adjustments to some of the variables as scholars attempted to account for the moon’s motion. However, they were looking for a single term to apply to all cases, not realising that the change they were looking for is not uniform.

When the computer was developed, the complexities of the Earth’s rotation and the Moon’s motion could be determined far more rapidly, and therefore algorithms could be developed, tested, altered, and re-tested on time-scales that would have been in-

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conceivable previously. In particular, the work of astronomers such as L.V. Morrison, F.R Stephenson, J. Meeus and F. Espenak has led to the generation of new eclipse data, thus removing our reliance on 19th-century canons. The accessibility of computing resources means that a historian, with only a little understanding of astronomy, can access some of the most up-to-date solar and lunar eclipse data through the National Aeronautics and Space Administration (NASA) website and easily compare data for different locations using its JavaScript Eclipse Explorer23. This does not compute the eclipses themselves, but draws on pre-determined data on the position of the sun and moon, and calculates the positions in the sky as viewed from a specified location. It then determines the time of the start and end of the eclipse, the amount of the solar or lunar disc covered during the greatest phase of the eclipse, and the position of the bodies in the sky at key times. This means that historians are no longer forced to search through Ginzel’s Spezieller Kanon for outdated information that only covers a few loca-tions, consult Oppolzer’s inaccurate maps, or even to ask an astronomer to calculate the data. The results can be checked personally, the dates and locations adjusted as desired, and the uncertainties incorporated into the analysis.

Determinations for the sighting of the first lunar crescent are very important, and al-though we can calculate the timing of a new moon conjunction to within a few seconds, and determine when the moon should cross the horizon and theoretically become vis-ible, it is impossible to predict what the weather conditions might have been at any point in the past, or when people actually saw it. Ancient methods of prediction, such as the Babylonian rule of thumb that if the moon set 48 minutes after the sun, then a new moon would appear the following night, were extremely unreliable with an error of 66° in longitude, and even the modern prediction criterion developed by B.E. Schae-fer has only reduced this error to 29° 24. Additionally, research shows that there is a 15% chance for a false sighting of a new moon crescent, the earliest the moon could be seen is 15 hours after the conjunction, and even an advanced crescent can be missed 2% of the time – not accounting for the unpredictable weather25. However, we do not always have to rely on calculations of probable sightings, as we have some records from the Middle Ages that are dated in more than one calendar and can provide synchronisms, as well as tables created by Muslim scholars to correlate between their calendar and the Julian26. For more ancient times, however, dates of events in lunar calendar months are not conveyed with synchronisms and therefore the precise start of the month is not known. The best scholars can do is allow between one and three days after the conjunc-tion as a guide; computer programs such as Redshift, Cybersky and Alcyone Astro-nomical Tables are able to provide dates and times for conjunctions.

The motions of the stars are much easier to replicate, and so the dates of the solstices and equinoxes are quite well established for the historic and prehistoric past. Although the dates vary due to a ‘wobble’ in the spin of the Earth, an effect known as preces-sion, this variation is very slight and predictable. The movements of the planets, while

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complicated, are also relatively straightforward to chart because their passage across the heavens is slower than that of the sun or the moon, which also means the uncertain-ties in calculations are smaller. By contrast, although computers have impacted a great deal on our understanding of comets, and increased our ability to compute their paths, the further back into history we look, the harder it is for us to determine how a given comet might have travelled. The problem is that comets are very small objects with long cycles, and easily perturbed by the gravitational fields of the planets in the solar system, especially Jupiter. Additionally, if the only information we have on a comet is a sighting which says that the comet appeared in the north and was visible at dawn for 26 days before disappearing, then that is not enough information to determine its exact trajec-tory or subsequent journey and thereby identify it27. The one exception to this is Comet Halley, whose spectacular reappearances have been charted since antiquity, and whose path is quite well understood. Our primary recourse therefore, when faced with a his-torical account of a comet that is not otherwise dated, is to compare it with Oriental records of unusual stars in the sky, which may provide us with an independent date.

Some astronomical resources are readily available online, including tools for convert-ing between calendars, and historical equinox and solstice dates, and can be found via an internet search engine. However, online tools and data for star positions, planetary,

Fig. 1The graphic user interface of Redshift 5.1

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solar and lunar movements and comets are only available for the modern period, and some for the early modern period, but no earlier.

For these periods, scholars must either install appropriate astronomical programs onto a computer, or turn to traditional published resources. There are a number of computer programs that allow someone with little astronomical knowledge to explore the his-toric heavens and witness what past observers might have seen. Redshift is one such program, whose easily navigated interface (shown in Fig. 1) allows you to input details such as the date you wish to observe, the place you wish to observe from, or the part of the sky you wish to look at. It allows you to approximate normal lighting conditions for the time of day, and locate specific objects in the sky. It also has a search function that means you can find all of the lunar eclipses, conjunctions or solstices in a given month, year, or longer period. It can tell you the sunrise and sunset times for any place on the globe at any time, and you can witness a reconstruction of any of these events. This puts all the answers at the fingertips of someone looking at a historical event with an astro-nomical observation tied to it. CyberSky and the Digital Universe perform the same tasks in a similar manner. However, they cannot account for observational factors, such as the distortion caused by the atmosphere. There are more technically advanced pack-ages available, but these include the most relevant information for historical research.

All of this is advantageous to the historian, as the results of ongoing research are avail-able in places other than astronomical journals and books, in a format that is accessible and understandable. A disadvantage, however, is that much of this is only available in English, especially the NASA data, and by necessity a certain amount of astronomical jargon is used, which the historian has to gain familiarity with. It is also difficult to determine the uncertainties in the data; for example, the NASA website discusses the algorithm used, and quantifies the uncertainties for 500-year periods, but this is not true for Redshift and most other astronomical packages28. The potential error in the position of the Moon in the sky can be up to 4° for 1000 BC, and although this de-creases closer to our own time, it can have a significant impact on the conclusions we are able to draw29. Thus it is important to note that, while astronomy can provide answers, those answers are not certain.

Jesus christ: A lifetime signified by the heAvens

In order to illustrate some of the tools mentioned above, and how they fit into histori-cal research and analysis, I am going to examine the life of Jesus Christ, which was as-sociated with several astronomical events. A star is reported at his birth, a lunar eclipse provides a means of dating the death of Herod, while Jesus’ death was timed according to the full Passover moon, and both a solar and lunar eclipse have also been associated with that event. These observations each require slightly different analyses and have dif-ferent value in terms of identifying the dates associated with his life.

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The Star of Bethlehem is a famous part of the nativity story, but appears only in the gospel of Matthew30. He describes how the Magi came from the east, having witnessed a star that foretold to them the birth of a king in Israel. This star has attracted a great deal of attention from historians and scholars alike because the ambiguity of Matthew’s text opens it to multiple interpretations. Suggestions for the star include a sighting of Venus, a comet (especially Halley’s Comet), a conjunction between two or three planets, an occultation by the moon (where the moon obscures a planet or star), meteors, fireballs, the stationary point of Jupiter, and a supernova31. Some theories combine a number of these events, with the first one usually acting as a warning to the Magi and heralding the next, and they all tend to fall between 12 and 5 BC32. However, because Matthew’s account provides no detail on the object, and no other evidence by which to date it, it is possible to justify almost any astronomical event as being the Star of Bethlehem.

In all probability, the star is actually a fiction, or a mythologized narrative inspired by the observation of an interesting star by the author or his source. Although usually por-tents of disaster, comets could be interpreted as heralding a new king – Mithridates VI of Pontus, for example – and the Magi were appropriate for those who noticed the sign because they were known as astrologers in antiquity, and they represented the fact that Jesus would bring outsiders into the faith. There is no reason to assume that either the star or the Magi themselves played any genuine role at the time of Jesus’ birth; the star is meaningful because of what it symbolises, not because it had chronological value.

According to the gospels, Jesus was born during the reign of Augustus in Rome and the rule of Herod the Great in Judea33. Later Christian authors assigned a range of dat-ing information to the birth of Jesus, usually the 41st or 42nd year of Augustus’ reign, which fall approximately between 4 and 2 BC, depending on when Augustus’ reign is considered to have started34. Other forms of dates tend to fall into the same bracket; for example, Julius Africanus puts Christ’s birth in the second year of Olympiad 194, which is 3/2 BC, and in agreement with Hippolytus35. Epiphanius includes the names of the consuls, Octavian (for the 13th time) and Silvanus, which is equivalent to 2 BC, but he also mentions that the Alogi place Jesus’ birth in the consulship of S. Camerinus and B. Pompeianus, which may be a corruption of Camerinus and Sabrinus, consuls for AD 936. The Chronicle of 354 gives the consuls as C. Caesar and L. Aemilius Paullus, who held office in AD 1, while Cassiodorus Senator gives C. Lentulus and M. Messala, who were the consuls in 3 BC. A thorough examination of this evidence can be found in J. Finegan’s Handbook of Biblical Chronology. Although these dates seem to generally coincide in 4 or 3 BC, some of the corroborating evidence supplied does not agree with this. For example, Eusebius equates the 42nd year of Augustus with the 32nd year of Herod the Great, which does not seem plausible within Herodian chronology37.

The primary evidence for the chronology of Herod the Great’s life and reign comes from Josephus’ Jewish Antiquities, the Herodian section of which is probably based on the testimony of Nicolaus of Damascus, a contemporary and close companion of Herod

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himself38. From that we have the following information: Herod was pronounced king of Judea in Rome by Mark Anthony and Octavian in Olympiad 184 (44-40 BC), in the consulship of Domitius Calvinus and Caius Asinius Pollio (40 BC)39. A few years later he took Jerusalem by force, when Marcus Agrippa and Caninius Gallus were con-suls (37 BC), on the anniversary of Pompey Magnus’ defeat of the same city 27 years earlier, in the consulship of Caius Antony (Hybrida) and Marcus Tullius Cicero (63 BC), in Olympiad 179 (64-60 BC)40. He died 37 years after the Romans declared him king, and 34 years after the siege of Jerusalem41. Since Josephus was probably counting inclusively, this puts Herod’s death in ca. 4 BC. Josephus’ chronology seems to be con-sistent here, especially when we take later events into consideration, such as the death of Herod’s son Philip the Tetrarch, who Josephus says died in the 20th year of Tiberius’ reign, having ruled his tetrarchy for 37 years42. Since Tiberius died in AD 37, having ruled for just over 22 years by Josephus’ reckoning, this puts Philip’s death in AD 33 or 34, and his inheritance in ca. 4 BC, which is consistent with the information given for Herod. However, this means that Eusebius’ equivalency between Augustus’ 42nd and Herod’s 32nd years cannot work, and is probably incorrect. A lunar eclipse at the end of Herod’s life, therefore, could form a useful benchmark in the chronological informa-tion, corroborating the date of his death.

The eclipse is not described by Josephus; he simply says that following the seditious ac-tions of the Jewish leaders Matthias and Judas, Herod ordered them burned to death, and the night they were executed there was an eclipse of the moon43. Herod was already dying at this point, and, according to Josephus, following the eclipse he attempt to alle-viate his sickness by following the routines laid out by his physicians and bathing at the hot springs of Callirhoe; he then returned to Jericho where he deteriorated further and began to issue unusual orders, including summoning all the men of Judea and shutting them in the hippodrome, then asking his sister and her husband to execute them upon his death. He also changed his will and died five days after having his son Antipater executed44. Following his death, his son Archelaus inherited half of his territory, includ-ing Judea, and proceeded to hold a sumptuous funeral for him, followed by seven days of mourning. He then approached his new subjects with a view to wooing them, but some of the associates of Matthias and Judas demanded reparation for their execution, and although Archelaus attempted to appease them, even delaying his journey to Rome to be formally acknowledged as the ruler of Judea, violence escalated until there was a massacre of Jews at the Passover45. This means that the eclipse occurred before that Passover, which was early enough for it to be the first Passover of Archelaus’ reign, since he had not yet been to Rome to be officially endorsed.

In order to look at this astronomical event, we have to make a number of assumptions beforehand. First, we need to assume where the eclipse was seen; we choose Jericho because the prisoners were explicitly transported there before their execution. How-ever, the location is not too important because lunar eclipses are witnessed at the same

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magnitude (the amount of the disc covered by shadow) across the half of the world in darkness, and the location only really matters if the eclipse is at sunrise. We also assume that the eclipse took place within a year or two of his death, in order for there to be plenty of time for the events related above to occur. A study by R.R. Newton showed that eclipses can become associated with events up to three years before or after they occurred, due to the nature of association in the human memory46. Finally, we cannot assume that the lunar eclipse was total because Josephus does not say that it was, but it must have been visible. We shall look at the years from 8 BC to 1 BC, which cover the proposed period in which Herod’s death fell, with a reasonable margin for error. To generate the data, we access the NASA Asian JavaScript Lunar Eclipse Explorer, where we can generate all of the lunar eclipse data for Jericho for the entire 1st century BC, and then excerpt the information from 8 to 1 BC – this is shown in Fig. 247. Note that astronomers use a negative number for the year starting from AD 1, so that -7 is 8 BC.

As you can see, there are 13 possible eclipses. Five can be eliminated immediately be-cause they are penumbral (those marked ‘N’ on the table). Fig. 3 shows the position of the sun, moon and Earth during a lunar eclipse; because the sun is so much larger than the Earth, the shadow cast by the planet is not completely dark, but has an area of lighter shadow at the edge. When the moon passes into this shadow, it becomes slightly dimmer and redder, but because lunar eclipses only occur when the moon is full, the change in light intensity is difficult to detect with the naked eye, and a similar discolou-ration can also be caused by the atmosphere, especially near the horizon. Eclipses that

Fig. 2All lunar eclipses visible at Jericho, from 8 BC to 1 BC (courtesy of F. Espenak, NASA/Goddard Space Flight Center).

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only fall into the penumbral shadow of the Earth, therefore, can be disregarded for our purposes as they would not be recognised as eclipses by an observer in antiquity.

There are eight eclipses remaining. Where the information is in light grey, those phases occurred below the horizon where they could not be seen, and therefore a further three can be eliminated: 4 April 6 BC, 17 July 2 BC and 29 December 1 BC. A lunar eclipse is noticeable to anyone looking at the moon during any stage of partiality or totality, but due to normal activity cycles most witnesses will only see one if it occurs during the earlier part of the night. The eclipse of 18 November 8 BC started late in the night, was quite small (with an umbral magnitude of 0.443) and took place several years before Herod’s probable time of death; the 13 March 4 BC eclipse was rather small and began in the middle of the night; the eclipse of 9 January 1 BC seems to have been several years into the reign of Archelaus – all of these are therefore unsuitable and can be elimi-nated. This leaves the lunar eclipses of 23 March 5 BC, which began shortly after rising, and that of 15 September 5 BC, which was later in the night but equally visible.

From the evidence that we have for the eclipse, it is not possible to determine with certainty which is the more likely candidate, as both allow enough time for the events related between the eclipse and the Passover massacre. Unfortunately, Josephus does not provide any indication of how much time those events took; at least a month is needed, and probably several months, but not as much as a year. This would suggest that the eclipse of 15 September 5 BC is the more likely candidate. However, the choice of this eclipse is problematic because Jericho was Herod’s winter palace, so he may not have been there in September, and six months is arguably too much time for the events described. For this reason, the eclipse of 13 March 4 BC is often favoured48.

However, lunar eclipses were often seen as portending disaster, and so the lunar eclipse before Herod’s death may not have originally coincided with the execution of Matthias and Judas, but later become associated with it after the execution came to spell disaster

Fig. 3The positions of the sun, moon and Earth during a lunar eclipse.

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for the Jews, culminating in a massacre at the following Passover. It seems probable that the eclipse occurred some time before Herod died, but not necessarily at the time of the execution. If this is the case, then it alleviates the problems with the chronology, as the executions could have taken place in the winter when Herod was at his winter palace in Jericho, and the time between the executions and the following Passover would be shorter than the six months that are necessitated by the eclipse in September 5 BC. Thus, it seems probable that the eclipse of 15 September 5 BC, or possibly the earlier eclipse of 23 March 5 BC, became associated with the executions of Matthias and Judas in the winter of 5/4 BC, and that Herod himself died in the late winter or early spring of 4 BC. This does not tell us when Jesus was born, however.

We turn now to Jesus’ death. Tertullian, Julius Africanus, John Philoponus, Origen and Eusebius associate a solar eclipse described by Phlegon of Tralles with the Crucifixion of Christ49. It is dated, according to the surviving sources, to Olympiad 202, which corresponds in the conventional chronology to AD 29-33. According to three of the gospels, during the Crucifixion there was an unnatural darkness from the sixth until the ninth hour, and an earthquake shook the temple, so it seems that the similarity with Phlegon’s description of the solar eclipse taking place at the sixth hour of the day and in conjunction with an earthquake in Bithynia, caused the two to become associated50. However, the darkness in the gospels cannot have been a solar eclipse, as the Cruci-fixion took place at the Passover, around the time of the full moon, and solar eclipses can only occur at the new moon, so the effect was meteorological in nature51. Unfor-tunately, Phlegon does not tell us where the eclipse was visible, but since both Bithynia and Tralles are in modern Turkey, it seems reasonable to suppose that the eclipse was visible there. It may also have been visible in Jerusalem, and become associated with the Crucifixion darkness in that way.

As a result, we need to look at the data for two geographical areas. This is easiest when looking at a map that shows all the relevant eclipses for the period we require, including AD 29-33. Using the NASA World Atlas of Solar Eclipse Paths, we can find the map for AD 21 to 40, shown in Fig. 452. Note that many of the other computer programs dis-cussed so far can also generate eclipse maps, but usually for a single eclipse at a time; the NASA data is more suitable for our purposes as it provides an immediate overview.

The immediately apparent answer is the eclipse of 24 November AD 29, which is the only one that was total in Turkey during this period, and by chance also passes close to Israel. The lines on the diagram show the path of the total phase of the eclipse, but the partial phases would be much wider. Therefore, if we use the JavaScript Solar Eclipse Explorer we can find that the maximum magnitude for this eclipse at Jerusalem was about 0.91, which is relatively large, but may not have been especially visible. Due to the incredible intensity of the sun, solar eclipses are not visible to the naked eye until they are quite advanced. For the trained observer, they become apparent from magnitudes of about 0.75, for the untrained, or unsuspecting, observer the Sun has to be 0.90-0.95

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eclipsed. This may seem surprising, but anyone who has seen an eclipse can verify that without special observing equipment, a partial solar eclipse is difficult to detect. In an-tiquity, the partial phases could have been observed in a reflective surface such as pitch or water, but solar eclipses are rare enough that most people would not think to check for one.

The uncertainty margin only affects these magnitudes by approximately ±0.04, which means that it may have had a magnitude as high as 0.95 in Jerusalem. This is the only suitable eclipse in the right place – Bithynia or Tralles – at the right time, so it seems altogether likely that this is the eclipse that Phlegon recorded.

A question that arises is how an eclipse in November of Olympiad 202 came to be asso-ciated with the death of Jesus. In fact there are two different notices regarding Phlegon’s eclipse, Philoponus says it took place in the second year of Olympiad 202, and Eusebius in the fourth year, both of which are incorrect, since it fell into the first few months of the first year, which started around midsummer of AD 29. It seems probable that if

Fig. 4World solar eclipse paths, AD 21-40 (courtesy of F. Espenak, NASA/Goddard Space Flight Center).

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the date was originally recorded correctly, it was later corrupted. This may have been deliberate, because Jesus’ ministry was assumed to have started in Tiberius’ 15th year, which is AD 28 to 29, in the same Olympiad as the eclipse53. The usual time given for that ministry is either one year, as implied by the three synoptic gospels, or three years, as implied by John. Therefore, if the notice for the eclipse was originally simply for Olympiad 202, it could have been interpreted as occurring in the second year to accom-modate a one-year ministry, or the fourth year to accommodate a three year ministry. Such manipulation of the date of the eclipse indicates that the later Christian writers had no more information by which to date Jesus’ lifetime than we do, but attempted to reconcile and synchronise the evidence nonetheless.

Those who follow Humphreys and Waddington interpret the descriptions of the signs signalling the end of days as indicating that there was a lunar eclipse during the Crucifix-ion54. The conventional date for the Crucifixion is 3 April AD 33, and that there was a lunar eclipse that night is used as confirmation of the date. The NASA JavaScript Lunar Eclipse Explorer suggests that the moon was partially eclipsed when it rose that night, reaching an altitude of 2° (±1.5°) when the partial phase ended, about 15 minutes after sunset, which suggests this eclipse would not have been particularly noticeable. There are other lunar eclipses that could have occurred during the Passover full Moon – 25 April AD 31 and 23 March AD 34, for example – but the evidence cited in favour of such an eclipse is not worth taking seriously. Had the moon turned to blood the night after Jesus was crucified, it is doubtful that any of the gospels would have omitted it.

We turn now to the evidence for the time of the Crucifixion. The gospels indicate that Jesus died after John the Baptist, and that John disputed the marriage between Antipas, tetrarch of Galilee and son of Herod, and Herodias, Antipas’ brother’s former wife55. John was executed by Antipas, and his death is discussed by Josephus, which brings the gospel narrative into direct contact with the historical evidence56. Although this has been used to establish a date for John the Baptist, there are two distinct chronologies, based on different interpretations of the available evidence.

Josephus tells us that Antipas married Herodias after he met her on a visit to Rome, and that she set aside her husband Herod, whom Mark calls Philip, to marry him. Antipas already had a wife, the daughter of Aretas IV of Nabataea, who learned of Antipas and Herodias’ intended marriage and fled to her father. Antipas and Aretas were already in dispute over the territory of Gamilitis, so Aretas used the treatment of his daugh-ter as the impetus to invade, and he defeated Antipas’ forces. Antipas then appealed to Tiberius, who in turn sent the Roman legions to aid him, but when the soldiers reached Jerusalem they received notification that Tiberius had died, and the new em-peror Caligula had recalled them. This was also about the time that Pontius Pilate left Jerusalem for Rome. Since Philip the Tetrarch, another son of Herod, had died some time previously without an heir, Caligula granted control of his tetrarchy to his friend Agrippa, the brother of Herodias. This enraged Herodias because he had been poverty-

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stricken and luckless for a long time, and so she encouraged Antipas to appeal to the emperor and claim Philip’s lands. However, Agrippa managed to contact the emperor first, claiming that his brother-in-law consorted with enemies of the state, so Caligula exiled Antipas and Herodias. Thus the territory of Galilee passed to Agrippa along with Philip’s lands57.

This narrative causes some problems because the gospels and the Slavonic version of Josephus say that Herodias’ former husband was Philip the Tetrarch, but Josephus says it was someone called Herod58. The usual solution is to assume he was called Herod Philip, that he lived in Rome and had fallen into obscurity after his father’s death. As a result, the marriage between Antipas and Herodias cannot be dated, so the Crucifixion is fixed by the testimony of St. Paul, whose own chronology suggests that he converted to Christianity in AD 34, after the Crucifixion59. However, the narrative would make more sense if Herodias had been married to Philip the Tetrarch: after his death, Antipas would have gone to Rome to ask for Philip’s lands, and there he could have met the wid-owed Herodias. They married for political convenience, but fell foul of John the Baptist who preached that their marriage was in violation of Levirate Law because Herodias and Philip had had a daughter60. The land of Gamilitis that Antipas and Aretas were disputing was actually part of Philip’s tetrarchy, so they would not have been disputing it had Philip been alive. After Antipas’ defeat, and Agrippa’s subsequent instalment in charge of Philip’s lands, Antipas and Herodias appealed to the emperor because they felt they had a stronger legal claim to the land than Agrippa due to their multiple fa-milial bonds to Philip61. The reason that Josephus would have obfuscated the truth of the matter is because Agrippa’s son, Agrippa II, was his patron, and if he were to tell the truth about the events leading to his father’s acquisition of the territories of Philip and Antipas, it would have seemed unjust and illegitimate, and not flattering to his patron. There is evidence that Josephus adjusted the truth in this way in other places in his Jew-ish Antiquities and Jewish War, and his portrayal of Philip the Tetrarch as a wise and kindly leader suggests that there was some bias to his account62.

If we follow this chronology, then it appears that John the Baptist offended Antipas af-ter Philip the Tetrarch died in AD 33 or 34, and both he and Jesus died before Agrippa took control of Philip’s tetrarchy in AD 37 when Caligula came to power. Although Josephus places the death of John before Aretas’ invasion, the timing is not necessarily accurate because Josephus has a tendency to summarise a series of events that span a period of time in a single place in the narrative, thus making it difficult to tell how they interrelate63. For example, the narrative about Jesus – assuming that it is original – ap-pears before the story of John the Baptist, and discusses his works, death and legacy64. There are no indicators as to the time of year that John died, but it seems probable that it was at least AD 34, and there needs to have been enough time after Philip’s death for Antipas to travel to Rome and marry Herodias, and for John to preach against them until he was incarcerated and executed. Since Jesus died at a Passover some time after

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this, he could only have died in AD 34, 35 or 36, as Tiberius died in March AD 37, before the Passover of that year.

The exact timing of the Crucifixion is difficult to determine because of the nature of the Jewish calendar in relation to the Julian, even if we think we can identify the cor-rect year. The Passover festival takes place on the 15th day of the Jewish month Nisan, which usually coincides with the full moon but is actually determined by the sight-ing of the new moon crescent. There is a degree of uncertainty in the determination of a historical Passover because we are not certain exactly how the festival related to the equinox in this period, how accurately the equinox was determined, and when the new moon crescent might have been sighted65. Additionally, the gospels disagree as to which day of the month Jesus was crucified: the synoptic gospels indicate 14 Nisan, but John indicates 15 Nisan66. The reason for this discrepancy is uncertain, and much debated, but for the purposes of this discussion we will use 15 Nisan. All the gospels agree that the Crucifixion took place the day before the Sabbath, which we equate to a Friday; this piece of information has been used in the past to determine the date of the Crucifixion by looking for when 15 Nisan falls on a Friday in March or April, and usually leads to the conclusion that Jesus was crucified on Friday 3 April AD 3367. How-ever, it is an assumption that the day before the Jewish Sabbath in the 1st century AD can be equated with our Friday, and an additional assumption that the sequence of days has been unbroken since that time. Although it is possible to argue with some validity

Fig. 5New moons, full moons and vernal equinoxes in spring, AD 30-37.

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that the Crucifixion actually took place on a Wednesday or Thursday, knowing the day of the week is not beneficial due to the uncertainties in the lunar data, since the start of the month could vary from the conjunction by up to three days.

To examine the astronomical data, we need to know the time of the vernal equinox, as well as the new moons and full moons for March, April and May in a number of years. We can use Redshift’s search function to find the required information and compile it into a table such as the one shown in Fig. 5. The dates in the ‘Earliest Date for 15 Nisan’ column are not necessarily the same as those in the ‘Full Moon’ column because of the uncertainties already discussed. Although we have a range of dates for each spring’s new moons, and probable dates for the Passover feast, we have no means by which to distin-guish between them, especially since the Crucifixion taking place on a Friday is not a reliable indicator. The astronomical data does not make things clearer than the histori-cal evidence, contrary to the usual interpretation of the material. It seems most likely that Jesus was crucified in AD 35 or 36, and that therefore the Crucifixion took place in April, but unfortunately the evidence is too uncertain to draw any firmer conclusions and the new moons cannot be said to substantiate a given claim.

Having established that Herod probably died in 4 BC, that Jesus died in 35 or 36 AD, and dismissed the lunar and solar eclipses connected with the Crucifixion, we still have not examined all the evidence that might help us to establish when Jesus Christ was born. Luke tells us that Jesus was about thirty when John the Baptist started his Minis-try in Tiberius’s 15th year (AD 28/9), and this is usually the age used to determine the temporal limits of Jesus’ lifetime68. There is also a reference to Jesus’ age in John, where the Jews say to Jesus, “You are not yet fifty, and you have seen Abraham?” which is usu-ally emended to ‘forty’, to agree with the Luke date69. However, there is no compelling reason to favour Luke over John in this respect, as the author of Luke is canonically considered to be St. Paul’s physician, and therefore never to have met Jesus, whereas the author of John, who may be John the Evangelist, claims to have done so. St. Irenaeus felt that Jesus was in his forties when he died, and argued against the idea that he was in his thirties70. Jesus confronted the moneychangers in the temple in Jerusalem and told them that he would tear down the temple and rebuild it in three days, and N. Kokkinos interprets their reply, that the temple “was being built for 46 years”, as being connected with Jesus’ age71. He argues that this is a play on words, as standing in the temple and claiming to tear it down, while actually referring to his body, is a parallel that would only work if he and the temple were the same age. This corroborates John 8:57 and has been used in conjunction with the date of the building of the temple to establish the date of the conversation. The chronology of the temple’s construction is complex, as Josephus tells us that Herod the Great decided to rebuild it in his 18th year (ca. 23 BC) and then waited until all the materials were ready before dismantling the old temple and commencing the new construction. Different parts of the temple took different amounts of time to complete: the sacred area took only 18 months, while the majority

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took 8 years and some took much longer72. This provides a date between ca. 19 and ca. 12 BC for the completion of the temple, which dates the conversation to between AD 27 and AD 34, but based on the proposed chronology, it seems plausible for the temple to have been considered ostensibly complete from 12 BC, and for the conversation to have taken place in AD 34, when Jesus was 46 years old. This seems consistent with the chronology, but is not built on very firm evidence.

The apographe [enrolment] mentioned by Luke as the reason for Mary and Joseph be-ing in Bethlehem for Jesus’ birth is of little assistance in confirming the date because there is nothing in the historical record to corroborate it73. A number of solutions have been suggested, including a census by Saturninus in 7 or 6 BC, and an oath of allegiance in 3 BC, but none of these are conclusive74. In fact, it is entirely probable that the fam-ily were not in Bethlehem for Jesus’ birth, but that this is part of the mythologized narrative that establishes Jesus as fulfilling the prophecies of Isaiah, which said that the messiah would be born in the city of David, i.e. Bethlehem75. The census is therefore an excuse for Jesus to have been born in a town that was not Nazareth, his home; a similar event can be seen in Matthew, where Jesus is said to have been taken to Egypt in fulfil-ment of a prophecy that said he would be called out of Egypt76. Like many Jews of his era, Jesus paid little regard to the date of his birth, and this is why we do not know when it fell. None of the nativity stories can be assumed to contain useful chronographical information, and the same is true for much of the material relating to Jesus’ adult life because the sequence of events in the gospels were inspired by Jewish feasts and liturgi-cal readings, and therefore do not reflect a true chronology of events77.

Although non-Biblical historical evidence is essential for dating the key events in Jesus’ life, it cannot be assumed to be more reliable than the gospels without deeper analysis. This is also true for the astronomical evidence, which is always in danger of being vaunt-ed too highly. Astronomy is very precise, but it is accuracy that is of greater importance. We still have to argue through uncertainty to probability, and as much as we are aware of biases in the sources, we have to be aware of our own tendency to trust astronomical information too much. The conclusion that Jesus was crucified in either AD 35 or 36 is based primarily on the historical evidence, because the astronomical evidence – con-trary to many previous analyses of the information – is not certain enough to provide definite answers. Thus, although we have access to the astronomical tools to manipulate and examine the evidence for ourselves, we must be aware of the context of the astro-nomical data as well as the historical. Ambiguously described events such as the star of Bethlehem can only be identified with any certainty if there is a short span of time to consider. A date in an observational lunar calendar cannot be fixed into the Julian calendar without an uncertainty of two or three days, unless there is a synchronism to work from. Spectacular events, such as lunar and solar eclipses, are distorted in human recollection and often associated with events that were not coincident with them. All

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of this needs to be borne in mind when assessing historical and astronomical evidence, in order to avoid drawing overly certain conclusions.

conclusions

From this discussion, I hope that the reader is better able to appreciate the range, value and versatility of the astronomical resources available to the historian. Calendars are based on astronomical observations, and so by understanding those observations, we are able to turn to a number of tools that allow us to examine the data for ourselves. Interdisciplinary research is increasingly valuable, but we do need to familiarise our-selves with the skills and techniques of other disciplines before embarking on enquiry. A problem with using astronomical evidence is that it gives the impression of absolute certainty, but there are errors and uncertainties involved, just as there are with histori-cal sources. As historians, we should not be dazzled by the accuracy and precision of science, but embrace the opportunity to frame our own questions, to look down blind alleys and ponder the possibilities by manipulating the most up-to-date results avail-able. The research that we conduct into historical chronology also feeds back into as-tronomical research, as information such as the changing speed of the rotation of the Earth, for example, could not have been determined without access to the historical records and the chronological sequence of events in the first place.

Computers have more than just permitted additional computations to take place; they have increased the accuracy and speed of calculation, and opened up new resources to a wider audience. While I have been emphasising the use of computer- and internet-based programs for chronographical and calendrical purposes, they can also be used in other ways. Astronomical programs can be used to generate statistical information, check temple alignments, consider the significance of the timing of religious festivals, compare the night sky between different locations and different times, and much more. All of this can shed light on the relationship between religion, calendars and society, which have important links, both today and in the past.

notes

1 See the chapter in this volume by R. Ríos de la Llave, Using Internet Resources for Researching Religious History: the Dominican Order in medieval Spain as a case study, in which the author gives a thorough and detailed discussion of the online resources available using her own research as an example. In par-ticular, she gives an overview of the availability, value and limitations of these resources, which are applicable to all historical research conducted using the internet.

2 Hesiod, Works and Days 448-51; 564-570.3 R. Hannah, Greek and Roman Calendars: constructions of time in the classical world, London 2005, p.

116; for a good overview of the Labours of the Months see B.A. Henisch, The Medieval Calendar Year, Pennsylvania 1999.

4 Hesiod, Works and Days 770-1, 803-804.

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5 Plato, Laws 1.767c.6 See Hannah, Calendars cit.; W.K. Pritchett, O. Neugebauer, The Calendars of Athens, Cambridge, MA

1947.7 Aristotle, Athenian Constitution 43.2; Hannah, Calendars cit., p.45.8 Aristophanes, Clouds 580-590: he complains that the gods are going without their meals, which is at-

tributed to calendrical confusion by modern scholars, e.g. B.L. van der Waerden, Greek Astronomical Calendars and their Relation to the Athenian Civil Calendars, in “Journal of Hellenic Studies”, 1960, 80, pp. 168-180, p.175.

9 For more detail, see J. Finegan, Handbook of Biblical Chronology, Princeton 1964; S. Stern, Calendar and Community, Oxford 2001.

10 This information comes from eclipse records. See Livy 37.4 (190 BC), and E.J. Bickerman, Chronology of the Ancient World, London 1980.

11 D. Feeney, Caesar’s Calendar: ancient time and the beginnings of history. Los Angeles 2007, pp. 157-163.

12 See A.K. Michels, The Calendar of the Roman Republic, Princeton 1967; Feeney, Caesar’s Calendar cit.

13 See R.D. Ware, Medieval Chronology: theory and practice, in J.M. Powell (ed.), Medieval Studies: an introduction, Syracuse 1976, pp. 213-237 or R. L. Poole, Medieval Reckonings of Time, London 1918, for an overview.

14 C. Hignett, Xerxes’ Invasion of Greece, Oxford 1963, pp. 210-211; L. Magini, Astronomy and the Calen-dar in Ancient Rome: the eclipse festivals, Rome 2001, pp. 46-47.

15 A. Salt, E. Boutsikas, Knowing When to Consult the Oracle at Delphi, in “Antiquity”, 2005, 79, pp. 562-572.

16 Livy 9.46; D.E. Duncan, The Calendar, London 1998, p. 44.17 Stern, Calendar and Community cit.18 Duncan, Calendar cit., pp. 116-117. This attitude is expressed clearly by Pope Gregory I.19 J. van Goudoever, Biblical Calendars, Leiden 1961, pp. 279-280.20 Livy 44.37; D.J. Schove, Chronology of Eclipses and Comets AD 1-1000, Woodbridge 1984, p. 296.21 O. Neugebauer, A History of Ancient Mathematical Astronomy, New York 1975, p. 82.22 T.R. von Oppolzer, Canon der Finsternisse, Vienna 1887; F.K. Ginzel, Spezieller Kanon der Sonnen-

und Mondfinsternisse: für das Ländergebeit der Klassischen Altertumswissenschaften und dem Zeitraum von 900 vor Chr. bis 600 nach Chr., Berlin 1899.

23 See F. Espenak, NASA Eclipse Home Page [online], NASA 2007 [cited January 2008]. Available from: <http://sunearth.gsfc.nasa.gov/eclipse/eclipse.html>.

24 B.E. Schaefer, Lunar Crescent Visibility, in “Quarterly Journal of the Royal Astronomical Society”, 1996, 37, pp. 759-768.

25 L.E. Doggett, B.E. Schaefer, Lunar Crescent Visibility, in “Icarus”, 1996, 107, pp. 388-403; Schaefer, Lunar Crescent cit., p. 759.

26 G.S.P Freeman-Grenville, The Islamic and Christian Calendars: AD 622-2222 (AH 1-1650), Reading 1995.

27 The example is the comet of AD 389, described by Marcellinus, Chronicon 2.62.28 F. Espenak, Uncertainties in Delta T [online], NASA 2007 [cited January 2008]. Available from:

<http://eclipse.gsfc.nasa.gov/SEcat5/uncertainty.html>. The NASA site also indicates the change in

Alexandra Smith54

the Earth’s rotation, which is visible as an arrow along the top axis of maps, such as the one shown in Fig. 4.

29 For a fuller discussion of the errors, see L.V. Morrison, F.R. Stephenson, Historical Values of the Earth’s Clock Error ∆T and the Calculation of Eclipses, in “Journal for the History of Astronomy”, 2004, 36, pp. 327-336.

30 Mt 2:1-9.31 A typical range of suggestions includes: F.J. Tipler, The Star of Bethlehem: a type-Ia/Ic supernova in the

Andromeda galaxy, in “Observatory”, 2005, 125, pp. 168-173; M. Kidger, The Star of Bethlehem: an astronomer’s view, Princeton 1999; G.B. Baratta, A New Determination of the Birth Year of Jesus Christ, in “Vistas in Astronomy”, 1995, 39, p. 721; I. Bulmer-Thomas, The Star of Bethlehem – Stationary Point of a Planet, in “Quarterly Journal of the Royal Astronomical Society”, 1992, 33, pp. 363-374; C.J. Hum-phreys, The Star of Bethlehem – A Comet in 5 BC – and the Date of the Birth of Christ, in “Quarterly Journal of the Royal Astronomical Society”, 1991, 32, pp. 389-407; K. Ferrari-D’Occhieppo, The Star of the Magi and Babylonian Astronomy, in J. Vardaman, E.M. Yamauchi (eds.), Chronos, Kairos, Christos: the nativity and chronological studies, Winona Lake 1989, pp. 41-53; J. Thorley, When was Jesus Born?, in “Greece and Rome”, 1981, 28, pp. 81-89; J. Seymour, M.W. Seymour, The Historicity of the Gospels and Astronomical Events Concerning the Birth of Christ, in “Quarterly Journal of the Royal Astronomi-cal Society”, 1978, 19, pp. 194-197; D.H. Clark, J.H. Parkinson, F.R. Stephenson, An Astronomical Re-Appraisal of the Star of Bethlehem – A Comet in 5 BC, in “Quarterly Journal of the Royal Astronomical Society”, 1977, 18, pp. 443-449.

32 E.g. Kidger, Star of Bethlehem cit.; Ferrari-D’Occhieppo, Star of the Magi cit.; Thorley, When was Jesus Born? cit.; Humphreys, Star of Bethlehem cit.

33 Mt 2:1-2; Lk 1:5-36, 2:1-2.34 Augustus’ 41st year: Cassiodorus Senator, Chronica; Irenaeus, Adversus Haeresis 3.21.3; Tertullian, An-

swer to the Jews 3.151 n.1. Augustus’ 42nd year: Clement of Alexandria, Stromata 2.168; Epiphanius, Panarion Haeresis 51.22.3; Eusebius, Praeparatio Evangelica 1.5.2.

35 Julius Africanus, Chronographies 5500; Hippolytus, Chronicle 5502.36 Epiphanius, Panarion Haeresis 51.22.3.37 Eusebius, Chronicle.38 See R.J.H. Shutt, Studies in Josephus, London 1961; M. Toher, Nicolaus and Herod in the ‘Antiquitates

Judaicae’, in “Harvard Studies in Classical Philology”, 2003, 101, pp. 427-447.39 Josephus, Jewish Antiquities 14.15.5; T.R.S. Broughton, The Magistrates of the Roman Republic. Volume

II: 99 B.C. - 31 B.C., New York 1952, p. 378.40 Josephus, Jewish Antiquities 14.16.4; 14.4.3.41 Josephus, Jewish Antiquities 17.8.1.42 Josephus, Jewish Antiquities 18.4.6.43 Josephus, Jewish Antiquities 17.6.2-4.44 Josephus, Jewish Antiquities 17.5.1-17.8.2.45 Josephus, Jewish Antiquities 17.8.3-17.9.3.46 R.R. Newton, Two Uses of Ancient Astronomy, in F.R. Hodson (ed.), The Place of Astronomy in the An-

cient World, London 1974, p. 101-106.47 Eclipse predictions courtesy of F. Espenak, Javascript Lunar Eclipse Explorer for ASIA [online], NASA

2007 [cited January 2008]. Available from: <http://sunearth.gsfc.nasa.gov/eclipse/JLEX/JLEX-AS.html>.

Calendars, Chronology and the Life of Jesus Christ 55

Antiquity

48 See Finegan, Biblical Chronology cit.; D. Johnson, ‘And they went Eight Stades toward Herodeion’, in J. Vardaman, E.M. Yamauchi (eds.), Chronos, Kairos, Christos: the nativity and chronological studies, Winona Lake 1989, pp. 93-99; E. Schürer, Geschichte des Jüdischen Volkes im Zeitalter Jesu Christi. 1. Einleitung und politische Geschichte, Leipzig 1890.

49 Phlegon of Tralles, Olympiads Fragment 17; Eusebius, Chronicle; John Philoponus, De opificio mundi 2.21; Julius Africanus, Chronographies 5500; Origen, Contra Celsum 2.33; Tertullian, Apology 21.19.

50 Mt 27:45, 27:50-54; Mk 15:33-38; Lk 23:44-46.51 See Schove, Chronology cit., p. 6.52 From F. Espenak, NASA World Atlas of Solar Eclipse Paths [online], NASA 2003 [cited January 2008].

Available from: <http://sunearth.gsfc.nasa.gov/eclipse/SEatlas/SEatlas1/SEatlas0021.GIF>.53 Lk 3:1-3. This is actually given as the date for the commencement of John the Baptist’s ministry, rather

than Jesus’.54 Acts 2:20; C.J. Humphreys, W.G. Waddington, Dating the Crucifixion, in “Nature”, December 1983,

306, pp. 743-746.55 Mk 6:17-18; Mt 14:3-5, 12; Lk 8:7-9.56 Josephus, Jewish Antiquities 18.5.2.57 Josephus, Jewish Antiquities 18.5.1-7; Mk 6:17.58 The passage is preceded in the Greek by Josephus, Jewish War 2.9.5-6. See H. Leeming, K. Leeming

(eds.), Josephus’ ‘Jewish War’ and its Slavonic Version, Leiden 2003.59 Gal. 1:18, 2:1. St. Paul claims to have returned to Jerusalem after an absence of 14 years, which would

place his original visit in AD 34, but it is possible that ‘14’ is a textual corruption.60 Deut 25:5ff.61 Thanks to P. Smith for suggesting this interpretation of Josephus’ testimony.62 See Shutt, Josephus cit. pp. 90-91; Toher, Nicolaus and Herod cit.; M. Broshi, The Credibility of Josephus,

in “Journal of Jewish Studies”, 1982, 33, pp. 379-384; H. St. J. Thackeray, Josephus: The Jewish War, Books IV-VII, London 1967.

63 Josephus, Jewish Antiquities 18.5.2.64 Josephus, Jewish Antiquities 18.3.3. For a discussion of the origin of the passage regarding Jesus, see G.

Vermes, The Jesus Notice of Josephus Re-Examined, in “Journal of Jewish Studies”, 1987, 38, pp. 1-9.65 Finegan, Biblical Chronology cit., p. 44; R.T. Beckwith, Cautionary Notes on the Use of Calendars and

Astronomy to Determine the Chronology of the Passion, in J. Vardaman, E.M. Yamauchi (eds.), Chronos, Kairos, Christos: the nativity and chronological studies, Winona Lake 1989, pp. 188-192.

66 Mt 26:17-61, 28:1; Mk 14:1-12, 16:1-2, 15:42-44; Lk 22:7-24; Jn 19:31, 19:38-20:1.67 For example, R.W. Husband, The Year of the Crucifixion, in “Transactions and Proceedings of the Amer-

ican Philological Association”, 1915, 43, pp. 5-27; R. von Hennig, Das Datum der Kreuzigung Christi, in “Astronomische Nachrichten”, 1931, 242, pp. 109-112; G. Ogg, Chronology of the New Testament, in M. Black, H.H. Rowley (eds.), Peake’s Commentary on the Bible, London 1962, pp. 728-732; Hum-phreys, Waddington, Dating the Crucifixion cit.; P.L. Maier, The Date of the Nativity and the Chronology of Jesus’ Life, in J. Vardaman, E.M. Yamauchi (eds.), Chronos, Kairos, Christos: the nativity and chrono-logical studies, Winona Lake 1989, pp. 113-130.

68 Lk 3:23.69 Jn 8:57.70 Irenaeus, Adversus Haeresis 2.33.4.

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71 Jn 2:19-20; N. Kokkinos, Crucifixion in A.D. 36: the keystone for dating the birth of Jesus, in J. Varda-man, E.M. Yamauchi (eds.), Chronos, Kairos, Christos: the nativity and chronological studies, Winona Lake 1989, p. 153.

72 Josephus, Jewish Antiquities 15.11.1-2, 15.11.5-6.73 Lk 2:1-2.74 Regarding Saturninus’ census, see Tertullian, Against Marcion 4.19; Finegan, Biblical Chronology cit.,

p. 237; H.W. Hoehner, The Date of the Death of Herod the Great, in J. Vardaman, E.M. Yamauchi (eds.), Chronos, Kairos, Christos: the nativity and chronological studies, Winona Lake 1989, pp. 101-111. For an oath of allegiance in 3 BC, see E.L. Martin, The Nativity and Herod’s Death, in J. Vardaman, E.M. Yamauchi (eds.), Chronos, Kairos, Christos: the nativity and chronological studies, Winona Lake 1989, pp. 85-92; Thorley, When was Jesus Born? cit., pp. 84-85.

75 Isa. 60:14.76 Mt 2:14-15.77 Goudeover, Biblical Calendars cit., pp. 280-283; B. van Elderen, The Significance of the Structure of Mat-

thew 1, in J. Vardaman, E.M. Yamauchi (eds.), Chronos, Kairos, Christos: the nativity and chronological studies, Winona Lake 1989, pp. 3-14; A.N. Wilson, Jesus, London 1992, pp. 51-53.

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