How long ago was 1 ad

The last is the most fundamental problem - even assuming we had extremely accurate dating technology, what would we use as our reference standard? Dating by astronomy doesn't solve this issue by itself. Say we knew this particular event happened in Rome roughly years ago, and on that day some astronomical event happened for which we could extrapolate the precise number of days back from today that it happened. How do we match up that date with the contemporary calendar?

Do you mean how do we figure out what day a Roman would say it was if you hopped back through a time machine to then? I'd guess we don't. What would the point be of knowing, now, that something happened 3 days before the ides of junius in AUC ? We'd probably just run our current Gregorian calendrical reckoning back to say that something happened on 20 July BC, or whatever, even though there was no month of July in BC. Maybe with whatever modifications it might need over really long timescales to keep it lined up with the equinoxes and solstices.

People from other cultures might well wind back the Islamic or Hebrew or whatever calendar to get a date that makes sense to them. If we drop the Gregorian system for something else, then we'd run that back through time instead. Astronomers might well not bother and just refer to things by their Julian day number.

Response by poster: it's made easier by the seasons. That's true, but even that alone doesn't necessarily mean that everyone would be keeping track of the year. For example, if you were in the year , you might well not have known how long ago anything was, even if you could tell the season. I think the way we are bombarded with the date everywhere these days, in the newspaper, the TV guide, TiVo, and weblogs conditions us to believe everyone has this same grasp on time, but back before these daily reminders, I'd like to imagine that long periods of time would have been rather vague to define.

I think it should be defined as relative to the date when Dionysius Exiguus came up with the idea in the 6th century. The convention is to use the Julian calendar when looking at historical dates during the period it was used. The date offset between it and Gregorian is the same everywhere, even if it was applied at different times between and , so it's trivial for dates before that period. Leap years being not exactly consistent in the Julian calendar does complicate things a little, but they were regular by the time our current method of counting years was invented.

I thought it was known when they occurred. But since 1AD was defined retroactively in a rather arbitrary fashion, how you should account for those leap years depends on whether Exiguus did so. This page says there are "a considerable number of theories" about how he fixed the day. At what point did people start using the AD system? That is, was it like some time in the s when someone said "Screw this, today isn't the 24th day of the second year of the reign on King Jackington, it's Tuesday, the 2nd of June, " or did it start much earlier, like in the s, etc.

In either case, did it carry forward uninterrupted or did at some point someone have to reconstruct today's date in the AD system and issue a press release telling everyone it was , not ?

Damned if I can find it now, though. Essentially, the calendar has been messed about with considerably over the last 2 millenia, but not quite as much as before for example, on moving to the Julian calendar, there was a year with days in it. The Julian calendar began in 45 BC, and the Romans and hence, the rest of Europe reckoned from this date so, AD 1 was year 45 of the roman calendar.

You have to go to the venerable Bede in about AD to the first usage of 'Anno domini' in the year of our lord itself. The 'AD' usage didn't become common usage until much later.

When Pope Gregory reformed the calendar, he removed 10 days from the calendar in October - so in October , you had the 4th of October followed by the 15th of October the following day.

The change was introduced largely to reconcile Easter with it's proper place in the year. There is no year AD 0, which complicates things a little the number zero was invented by the Indians in the 8th century - too late for the calendar. Other cultures use different calendars - the islamic calendar is purely based on the phases of the moon, the mayan calendar is based on the great cycle of about years, and I believe that the Ethiopians still use the Julian calendar, and it's also currently the early s there.

The French also attempted to decimilase the calendar after the French revolution - weeks were 10 days long, days were divided into 10 hours and minutes to each hour. Shame it never really took off. Ah, sorry, it's not Bede. Perhaps an excerpt from the book might help here: Dionysius complained that earlier Easter tables used a calendar widley followed at the time, which started at AD , the year the Emperor Diocletian ascended to the throne.

Under this system the year But Diocleatian was a notorious persecutor of Christians, noted Dionysius, who tells Petronius that he 'preferred to count and denote the years from the incarnation of our Lord' Dionysius calculated that Christ was born exactly years earlier - which became his base year of AD 1.

Where the aboot got this date for Christ's birth is unknown Dionysius was the first ever to use the system we all now take for granted when he wrote on his Easter tables anni Domini nostri Jesu Christi From reading stuff last night, it seems that it started taking off with Charlemagne and built from then on. A lot of wacky stuff that must have seemed like a good idea at the time has been done historically with calendars. My favourite warning on impossible dates: Indeed.

Sweden adopted the leap-year rule of the Gregorian calendar in , making it a non-leap year, but without adjusting the calendar otherwise, so that after that Sweden was out of sync with both Julian and Gregorian calendars. After a while they discovered it was not such a great idea, and in Sweden moved back to Julian calendar by adding an extra day to February, resulting in the unusual date of 30 February No, I meant, for example, that if both we and Dionysius who I take as having the last word on when AD 1 really was used this same great astronomical dating method to date some particular event around, say years ago, how could we be certain that both our and Dionysius's counting back the days to that event would hit the same point on our respective calendars relative to AD 1?

Would they both be the exact same distance from AD 1? In addition to the astronomical method we'd need something else. And if you really want to date things from the birth of the jesus, you're gonna run into some problems as the whole December 25th thing is an arbitrary day supposely chosen to be near winter Solstice for celebration, as we don't know when, exactly, he was born.

Let's assume there was a solar eclipse that we would place on 1 September AD 10, or Julian day What's your concern?

That Dionysius might have said that it was 11 September AD 10? The properties of the Julian and Gregorian calendars are well-known and converting between the two is just math. Therefore, it's easy to assume that A. To further complicate the matter, there's an ongoing debate over when Jesus was born. This is not provided in the gospels or any secular text.

Some scholars stick with A. A monk called Dionysius Exiguus calculated his own present year to be A. Counting from that year reaches the current year. You add one year every January 1. If you have a math problem that requires you to calculate years across B. For example, if you need to work out how many years are between January 1, B.

However, you still have to adjust for the absence of year 0. You do this by removing 1 from your answer, so minus 1 is The calculation is a little more complicated when you are calculating partial years across B. First, change the month of the year into decimal form. If 12 months is 1, then nine months is 0. Say you need to work out what calendar year was years before October A. The simplest method is to take the starting calendar year and figure out how much time has lapsed since January 1, A.

In other words, October in the year was 1, Then calculate This means 4, years before October A.