Please explain my confused me like I’m 5 (0r 4 or 6).
It depends which calendar you use! Every calendar picks a basically arbitrary system to uniquely identify each year, and in some of them “year 0” doesn’t refer to any year.
The Gregorian, for example, goes directly from 1 BC to 1 AD, since 1 BC is “the first year before Christ” and 1 AD is “the first in the years of our lord.” This doesn’t make much mathematical sense, but it’s not like there was a year that didn’t happen–they just called one year 1 BC, and the next year 1 AD.
ISO 8601 is based on the Gregorian calendar, but it includes a year 0. 1 BC is the same year as +0000; thus 2 BC is -0001, and all earlier years are likewise offset by 1 between the two calendars.
If ISO says there was a year 0, there was. There’s only one thing better than perfect : standardized !
I need my standardized fixed calendar now dammit
Yes. They skipped right over. It confused many people at the time: a whole year of their lives, gone. Many centuries later when zero was invented, an explanation was finally offered as to why that happened.
😂
Serious answer about what the year would have been in 1 AD, according to 63-year-old Emporer Augustus:
DCCLIV754 Ab Urbe ConditaThat means “from the founding of the city” - they based their calendar on the mythical founding of Rome, as calculated by Verro, who himself was not long dead at that point. Before that, they just counted the years of each person’s reign Japanese-style. Probably other people in the ancient world had older calendars.
For those who don’t know, the concept of zero wasn’t discovered until the sixth century in India, and then either transferred or rediscovered in about the eighth century in Arabia.
When you consider the time as a number line, years are not points at integers (which would in some way warrant a year 0), but rather periods between them. Year 1 is the period between 0 and 1, and before that was -1 to 0, or year -1. There is no year 0, because there isn’t anything between 0 and 0
That makes sense, but trying to square that off with the idea that the year 2000 is the start of the 21st century is hurting my head.
If year 1 is the 1st year, then surely the first year of the 21st century should be 2001?
Ohh, nice one!
The first convention is common in English-speaking countries, but the latter is favoured in, for example, Sweden (tvåtusentalet, which translates literally as the two thousands period).
I’m not sure that’s entirely true, most people in English speaking countries (and the world over) celebrated the millenium at the beginning of the year 2000.
The enumeration on the losing side of that debate is probably correct. But as a person who was in my early 20s in 2000, I’d like to offer what I will characterize as The Historical Context and Definitive Conclusion to This Debate.
No one actually gave a shit about that debate. Sure, it came up, but it did not alter anyone’s party planning. We weren’t actually celebrating the changing of the millennium, we were celebrating because we had a permission slip to do so. Any attempt to withdraw that permission was unwelcome.
In Paris on December 31st, 1999, at around 11pm local time, someone threw themselves in front of a metro. The trains were free that night (because it was the 100 year anniversary of their opening iirc), but because of that suicide, at least one of the train lines was substantially delayed. The streets from the center of the city to the north side were crowded well toward dawn as everyone chose to walk home instead of wait indefinitely in a stinky train station.
That person, who chose to end their life on the tracks that night, holds the core truth of the debate within his death: it’s a ridiculous debate and those who would fight for it should just stay the hell home and let the rest of us drink a lot and dance.
It should all be zero indexed. Positional number systems like we write with are (600=0600) but our language isn’t, which causes this problem. Basically, if 2004 is the 20th century the gospels took place in the 0th.
If year 1 is the 1st year, then surely the first year of the 21st century should be 2001?
It is. The system is confusing.
the idea that the year 2000 is the start of the 21st century is hurting my head.
That may be because it is not. The first century was years 1 to 100. The second was 101 to 200. The 21st is therefore 2001 to 2100.
What you’re probably referring to is the “cultural century” which was considered to have started when the lead digit changed from 1 to 2. The same thing happened quite recently when some people argued 2020 was the start of a new decade (again, it wasn’t)
I hate it when people say it wasnt the start of a new decade, it’s a shit argument, why does it matter what the first year was, 2014 - 2024 is also a decade, and 2pm aest September 22nd 2024 will also be the start of a new decade. There is nothing wrong with saying 2020 was the start of a new decade. (again, it was)
There are decades and there are decades. Just like there are weeks (period between Monday and Sunday inclusive) and weeks (any seven consecutive days).
When you say “I’ll do this next week”, then you mean the next period between Monday and Sunday. When you say you’ll do it in a week, it means you’ll do it after exactly 7 days from now, regardless of what day is it today. Same for decades.
You said start of a new decade, not the new decade in the original comment, they are very different
??? You know very well what I meant, be more forgiving to second-language speakers
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when I originally replied to you, I very obviously did not know that you meant that
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didn’t know you weren’t a native speaker either
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This explanation is unclear to me. Why do we choose the later of the two endpoints of the year for (0, 1) but the earlier of the two for (-1, 0)?
The language is rooted in the same logic as people. Your first year was between the ages of 0 and 1. The first year before you were born is between -1 and 0. There is no 0th year because 0 is a point in time and not a range in time.
Your explanation works equally well for any integer though. You could say the same of 1.
I think you’re saying that it’s a fencepost issue. But even for personal ages this doesn’t check out: for a year after you are born, your age is “0.” A one-year-old baby is in the following year.
I feel you’ve missed the point I was making and assumed I’ve made another. Age number and year number are different. You’re in your first year when your age is not yet 1. You’re in your second year when your age is between 1 and 2.
Years follow numbers as in "this year was the first/second/third year of ", not “this year was the year turned X years old”
Oh I see. Sure, historically it makes sense that years have been ordinal numbers. But in the modern era with all our math and computational knowledge, it is not convenient anymore. It means off-by-one errors are easy to commit when comparing BC and AD years.
This is why programming languages all index from 0 rather than 1 (knuth and lua be damned)
Absolute value. Both systems count time from the same epoch, or zero point.
One year before the epoch is 1 January 1BCE One year after the epoch is 31 December, 1CE.
Half a year before the epoch (-0.5 years) is June 30, 1BCE. Half a year after the epoch (0.5 years) is July 1st, 1CE. These dates occur within the first year before the epoch, and the first year after the epoch, respectively.
Because until the Middle Ages, Europeans were afraid of the number 0.
Moving from too… not too from
Remember originally that -1 was 1 BC, meaning 1 year before the birth of christ. The negative numbers are measuring the distance away from 0.
Edit: in the positive direction, the 1 was 1 AD, meaning the first year of our lord. Just like when talking about the reign of kings/queens, the first year of their reign is 1 and the 14th year that they reigned is 14. I believe the timekeeping for Ages in LOTR may also be similar.
For the same reason why 1.5 is on the right from 1 but -1.5 is on the left from -1
If we were starting from scratch, it would probably be better to go with two year zeroes, so it would fit normally into positional number systems, and then you could even talk about 0.5AD for the relevant summer.
Unfortunately, positional numbering wouldn’t be invented in the old world until hundreds of years after the Christian calendar.
The only positional numbering system I use daily (base 10) has only one zero. What system are you talking about?
Oh really? What do -0.25 and 0.25 both start with, and round to?
A reminder to read the original reply that started this thread. There’s two “zero-areas” between the one points and the zero point.
Ah, I see. You’re advocating for naming the intervals (0, 1) and (-1,0) by rounding toward zero rather than away from zero. I would advocate for rounding toward the lesser value: (-1, 0) -> “-1” and (0,1) -> “0”
That could work. Calculating across eras would still end up sort of funny (the putative nativity would be a year closer to 233BC than 233AD, for example), but unless you’re an archeologist that doesn’t come up that often.
I had another conversation about this not that long ago, and it really does boil down to treating intervals as numbers. Unix epoch doesn’t officially extend to pre-1970 years, but it’s defined as “the number of seconds that have elapsed [past perfect] since” for that reason, and does have a second 0. It fair to guess Bede himself didn’t properly distinguish between the two, because that leads directly to an argument 0 is a number, which AFAIK doesn’t appear in European mathematics until much later.
I think the only reason that the nativity would be a year closer to 233 ad than 233 bc is because Jesus was born in late December. Had he been born a week later on the 1st of January, it would work out, with 1 ad starting a year after his birth and 1 bc starting a year before (year 0 being that of his birth)
The year was built around it, not the other way. It’s all derived from the Christian calendar. I’m not sure off the top of my head how Christmas ended up a few days before New Years, but they’re deliberately very close. It has been argued that the real life birth might not have been in winter at all (or even Bethlehem).
I digress, though. It would inevitably be lopsided somehow, because you’ve centered the numbering system around six months off of the New Years points.
So in your idea there would be year +0 and year -0 before it, right?
Well, AD and BC(E) are the usual notation in this case, but yes. This is distinct from -0 and +0 in computation, because as OP says these are intervals rather than points.
floating point arithmetic on computers does suffer the existence of a negative zero. But it’s generally considered an unfortunate consequence of IEEE754.
Years exist. We decide what to call them. You and I agree to call this year 2024, but that’s only an agreement. Some people call this year 5784.
We call the system we use “The Gregorian Calendar”, because of a Pope named Gregory. That system is mostly the same as “The Julian Calendar”, with some important changes to make the calendar match the changing of the seasons better. In the Julian calendar, they decided to count the years starting from when they thought Jesus was born. They chose his birth year to be “The first year of our Lord”. We call that “year 1” for short.
The people who created that system (the Julian Calendar) didn’t understand 0. The year before “The first year of our Lord” was called “The first year before the birth of Christ”. We now call these “AD 1” (“anno domini”, because Latin) and “1 BC” (“before Christ”). Since they didn’t understand 0, they didn’t call any year “0”. We have kept the tradition, because reasons.
Some other systems have relabeled the year before “AD 1” as year 0, but that’s not how the Gregorian Calendar works, and that’s the calendar that you and I have been taught to use.
“They,” i.e. the catholic church, or whoever was tasked with coming up with a calendar, absolutely understood the concept of zero in the 1500’s. Yes, Zero took a bit longer to formalize and enter the zeitgeist of the public consciousness, but this myth of zero being some kind of unknowable thing for thousands of millennia is naive.
I’d go so far as to say that a year zero in a calendar is useless. There should be a starting point of course, but calling it yero zero instead of year 1 is dumb.
By that part, I was referring to the people establishing the Julian Calendar, not the Gregorian. I’ve edited my comment to clarify that.
But you are missing the point,. There is no reason to ever start a calendar at year zero. The starting point can be zero, fine, but once the first day goes by, you are in the first day of year 1, not year zero and that is logical and has nothing to do with smart astronomers etc, “not understanding the number zero.”
At this point I’d say the only person who doesn’t understand zero is you.
It makes sense to start with the year zero when you want to do any calculations that involve dates that where before and after year one. If an empire was founded in 50 BC and dissolved in 50 CE to calculate its age when it was dissolved you have to acknowledge that there is no year zero so instead of just calculating 50 - (-50) = 100 you have to substract one which is counter intuitive. Because it went from year 1 BC straight to 1 CE.
The length of time an empire existed isn’t really important in the study of history. You need to describe the contextual existence of the empire within history, and you do that by specifying the start and end dates (in whatever calendar system you want to use). Using your example, if you say that empire existed for 101 years, why is that significant? It’s not. But if I say that empire existed in the middle east during the time of Christ and Roman occupation of Palestine, THAT provides the important historical context for why that empire was significant, and what kind of importance it may have had.
https://en.wikipedia.org/wiki/Year_zero
The year of Jesus’ supposed birth was counted as year 1 AD/CE. The year before that is considered year 1 BC/BCE. It’s worth noting that the concept of zero didn’t yet exist back then. https://en.wikipedia.org/wiki/0#History
Probably worth noting that the Gregorian Calendar was an invention of the 16th Century. It was invented to deal with the problems of the Julian Calendar and the creators would have had a firm understanding of the concept of zero. The AD/BC split was all about the assumed year of the birth of Jesus of Nazareth (according to Christian mythology). The year of his birth was set as the first year Anno Domini or “The year of the Lord”. Or the first year where Jesus was kicking about. The year prior to that would therefore be the first year before “Before Christ” was alive, and therefore the year 1 BC.
Especially weird considering that Christmas has been set to December for a long time, so 98% of year 1 AD was actually before the ostensible birth of Christ (I know that scholars now think he was born in April or something, but they probably didn’t always)
Ultimately, they had to set the calendar’s dates based on something. Given the vast hold on Europe which Christianity had at the time, it’s not surprising that the starting date was based on such an important event in the mythology. However, trying to deviate too far from the currently understood order (the Julian Calendar) was likely to end in failure. So, they could either fight the tide of history or just accept a logical oddity. Given all the other logical oddities one must accept for supernatural belief, who’s going to complain about having a holy reason to eat, drink and be merry during one of the most terrible parts of the year?
ELI5 answer?
In the conventional calendar, there wasn’t a year zero and it wasn’t skipped. Zero is the moment in time that we use to begin counting time.
Think of an elementary school style number line:
…-3_-2_-1_0_1_2_3…Each number is one year apart. This makes the numbers measure something like Age. If you are 3 years old, you can count 3 years between 0 and 3.But a year is not an Age. It is the span of time between ages, and the years we name are actually the spaces between the numbers on the number line. So the first year (1 AD/CE) is the first space after zero (between 0 and 1), and the first negative year (1 BC/BCE) is the first space before the 0 (between -1 and 0).
Then there is the astronomical calendar, which does have a year zero. They get this by naming the year (the space on the number line) after the number to the right side of the space on the number line.
By this description, year zero is the time between the 0 and the 1 for the same reason the time between 10 and 11 is the year 10.
Your logic is correct, but you are off by 1.
0-1 is year 1
10-11 is year 11
i hope all these conflicting answers in the comments have made you less confused, OP.
😁
The anno domini (AD) dating system started in 525. The concept of zero did not make it to Europe until the 11th century.
Years are ordinal numbers, the kind of number that tells you which place you finished in a race, and as such cannot have zeroes or negatives. You’re living in the 2,024th year since the instant that began the Common Era. “0th” and “-1st” are not valid expressions for years for the same reason that you can’t place 0th in the Olympics
Programmer clutching their keyboards screaming “Arrays start at 0!”
Ordinals are largely used for counting and when you’re counting you kind of do start a zero, most people just don’t say it. When you count 1… 2… 3… it would work just as well to start 0… 1… 2… 3… So programmers can rest easy.
Nope. 1 BC/BCE -> 1 AD/CE. That’s just how it was designed.
The concept of zero had not even been discovered at the time the calendar was designed.
Almost. The first recorded use of ‘Zero’ was in Mesopotamia in 3BC/BCE. https://www.history.com/news/who-invented-the-zero
this is absolutely wrong.
When someone decides to change the way that they keep track of time, the new calendar typically starts at 1, as in “the first year of this new era”. It’s not that there was no existing year before that, just that it doesn’t make sense to start as zero.
It’s not like the Gregorian calendar that we use now existed in -1 and then rolled over to 0 and then 1. They just started the new one at 1, and for a period of time, there was surely some overlap in people using both calendars, until one was phased out entirely.
The year 1AD wasn’t called 1AD in 1AD. The system was invented hundreds of years later.
Korea kinda takes this to the extreme with birthdays.
They started the new one around 525 and just backed dated everything before then. Year 1 was never observed in the modern calendar system. Most other calendars started with a year 1 on the day the king decreed it so (often the day he became king)
They left out 0 from the list. It basically jumps from -1 to 1.
Arbitrary decision is arbitrary.
The switch to the current system of using the theoretical birth of Jesus as the start of our calendar occurred in the 6th century, 500 years after the fact. They picked a year based on what evidence they had for when the birth of Jesus occurred with a margin of error of about ~30 years.
When this occurred and we started observing years in Anno Domini, whatever local calendar was being used was immediately replaced by the year 525, and retroactively everything before that was assigned it’s proper year. This ends with AD 1 and directly starts with BC 1 going the other direction. No year 0 was observed in this switch.Also note that before this switch, years were often designated in relation to the founding of a city or by the start of a ruler’s reign. There were always ordinal numbers, so the first year of a reign would be year 1, and there was never a zero, because it was year X of a previous reign.
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CE/BCE isn’t strictly astronomical year terminology, it can be applied to the Gregorian calendar and AD/BC can be used for astronomical years. If you see BCE outside of an astronomy context, it probably does not include a year zero
