Please explain my confused me like I'm 5 (0r 4 or 6).
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
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)?
Because until the Middle Ages, Europeans were afraid of the number 0.
For the same reason why 1.5 is on the right from 1 but -1.5 is on the left from -1
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.
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.
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.
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
I’m no expert but I assume that the year Christ died would be “year zero” (assuming you’re talking about anno Domini (AD) and before Christ (BC)) since we started counting after that.
EDIT: reading more on the topic I might be completely incorrect with my above statement. If someone else knows, please do correct me
EDIT 2: I found this on Wikipedia which talks about a “year zero”
Zero exists, just not for the Gregorian calendar that follows the Anno Domini calendar numbering system (BC/AD). It is very true for Julian calendars that follow the astronomical year numbering system (BCE/CE) as well as Gregorian calendars that follow the ISO8601:2004 standard (no unit), as well as Holocene calendar, and numerous Hindu/Buddhist calendars.
1 BC = 0 BCE = 10000HE -> 1AD = 1CE = 10001HE
The anno domini (AD) dating system started in 525. The concept of zero did not make it to Europe until the 11th century.
They switched when years are counted. BC years are counted at the beginning of the year. AD years are counted at the end of the year.
The halfway mark in the first inch of a ruler is 0.5". The first inch ends at 1.00. 1.25" falls in the second inch of the ruler.
We recently completed the 3rd month in the 2024th year AD. We have not completed the full, 2024th year yet; but we are in it. This most recent April 1st was 2023.25.
1-Jan-1 BC was almost a year before 31-Dec-1 BC. 31-Dec-1 AD was a year after 31-Dec-1 BC.
Zero does exist in the astronomical year numbering system (BCE/CE as units, based on Julian calendar), as well as the Hindu, Buddhist, the modern ISO 8601:2004 (uses no units, based on Gregorian system) as well as the Holocene calendar (HE as unit).
It is just not in the old Gregorian and Julian calendar that uses the Anno Domini calendar year system (BC/AD). To make sense of it, 1BC follows 1AD. However, 0BCE follows 1CE. Also, in the Holocene calendar, it starts with -1HE.
Also, BC/AD and BCE/CE are not one and the same:
- 1BC = 0BCE = 10000HE
- 1AD = 1CE = 10001HE
The only difference between Julian and Gregorian calendar is that Julian leads the Gregorian calendar by 13 days - this holds true from 1901 to 2099.
