* * * * *
                                        
                 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. (Gnaeus) Pompeius Magnus and M. (Marcus)
> 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 [1], “M aking <time> safe for historians [2]”

This is an amazing article (long, but well worth reading) about the
difficulties historians have with time. Unfortunately, not only are calendars
complicated [3], but even the concept of time [4] is non-intuitive [5].

[1] http://news.ycombinator.com/item?id=5083628
[2] http://www.quirksmode.org/blog/archives/2009/04/making_time_saf.html
[3] http://www.tondering.dk/claus/calendar.html
[4] http://infiniteundo.com/post/25326999628/falsehoods-programmers-believe
[5] http://infiniteundo.com/post/25509354022/more-falsehoods-programmers-

Email Sean Conner at sean@conman.org

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