The Boston Diaries

The ongoing saga of a programmer who doesn't live in Boston, nor does he even like Boston, but yet named his weblog/journal “The Boston Diaries.”

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Saturday, January 19, 2013

So, what date did October 23, 4004 BC fall on?

Who needs machine readable dates? As far as I can see there are two target audiences for this operation. The first is obviously social applications that have to work with dates, and where it can be useful to compare dates of two different events. An app must be able to see if two events fall on the same day and warn you if they do.

However, as a target audience social applications are immediately followed by historians (or historical, chronological applications). After all, historians are (dare I say it?) historically the most prolific users of dates, until they were upstaged by social applications.

Let’s go another eight hundred years back and land just in time to see Hannibal victorious against the Romans at Cannae. This historical battle, sources assure us, took place on 2 August 216 BC. We don’t have a prayer of re-mapping this date to a proleptic Gregorian or a Julian one.

The ancient Roman year had 355 days, and in theory every second year ought to have a so-called intercalary month of 22 or 23 days. The problem was that these months were inserted irregularly, and no chronologist ancient or modern has ever taken the trouble to track down the exact use of the intercalary month. (Besides, the sources are just not there.)

This means that we will never know exactly on which proleptic Gregorian date the battle of Cannae took place. The best we can say is that it took place in high summer; probably in July or August.

Before Dionysius introduced his reform, people used the old Roman system, in which every year was named after its two consuls.

After the Romans had discarded their monarchy in 509 BC they were forced to stop using regnal years. They needed a new naming system, and they decided to allow their two chief magistrates, the consuls, to give their names to the year.

Thus, “in the consulate of Cn. Pompeius Magnus and M. Licinius Crassus Dives” is a historically valid alternative to “70 BC.” In fact, BC or AD years may be considered a convenient shorthand for the “semantically” more correct consular years.

Although the consuls lost all political power after Augustus founded the Empire in 27 BC, the title was still given out to aristocrats who’d deserved a plum, as wel as to the Emperor himself, until the office was abolished in 541 AD. The consuls continued to give their names to the year. (In return they were graciously allowed to squander their fortunes on organising circus games.)

Via Hacker News, M aking <time> safe for historians

This is an amazing article (long, but well worth reading) about the difficulties historians have with time. Unfortunately, not only are calendars complicated, but even the concept of time is non-intuitive.

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