In dating systems, zero year (LH:4) refers to the base year or year around which a dating system is structured, as in "years before", e.g. BC or BE, this base year, and "years after", e.g. AD or AE, the base year, the "base year" itself defined as year "zero", with years before and after counted as natural numbers, backward and forward, respectively.
The Dionysian calendar (BC/AC), invented in 525 AD (ADM), has no "zero year", as the zero concept, supposedly, was not yet realized, colloquially, at this period of time. Hence, the year of the myth of the birth of Jesus Christ is counted as 1AD, which was retrospectively, by five centuries, determined to align with the year or period (±5-years) of the zenith of power of the Roman empire, after the switch from Roman republic to Roman empire.
Hence, 1955AD is 0AE, 1956AD is 1AE, 1957 is 2AE, etc., and 1954AD is 1BE, 1953AD is 2BE, etc.
Haley comet | Defined
Note that the zero year of "1955" in ACM (or vulgar) years, alternatively, can also be taken as 32.293 Halley years (Halley sightings), time since 32nd recorded sightings of Halley's comet plus 21.975 solar years, where 1-sighting occurs every 75-years, since it's passing was first recording independently by Pliny the Elder and Chinese chroniclers. Meaning that "atoms were first seen" after 32.293 passages or sightings of Halley's comet. Herein, the BE/AE dating system is fully scientifically neutral and unbiased by anthropism, nationality, and or mythology.
The following are related quotes:
- “Herod died in 3BC, years before the supposed birth of Christ. Dionysius was clearly wrong; today most scholars believe that the birth of Christ was in 4 BC. Dionysius was a few years off. In truth, this mistake was not so terrible. When choosing the first year of a calendar, it really doesn't matter which year is chosen, so long as everything is consistent after that. A four-year error is inconsequential if everyone agrees to make the same mistake, as, indeed, we have. But there was a more serious problem with Dionysius' calendar: zero. There was no ‘year zero’. Normally this would be no big deal; most calendars of that day started with the year one, not the year zero. Dionysius didn't even have a choice; he didn't know about zero. He was brought up after the decline of the Roman Empire. Even during the heyday of Rome, the Romans were not exactly math whizzes. In the year 525, at the start of the Dark Ages, all Westerners clung to the clunky Roman style of numbers, and there was no ‘zero’ in that counting system. To Dionysius, the first year of Our Lord was, naturally, the year I. The next year was year II, and Dionysius came to this conclusion in the year DXXV.”
- — Charles Deife (2019), Zero: the Biography of a Dangerous Idea (pg. #)
- Seife, Charles. (2019). Zero: the Biography of a Dangerous Idea (pg. #). Souvenir.