Eli5: How did ancient civilizations in 45 B.C. with their ancient technology know that the earth orbits the sun in 365 days and subsequently create a calender around it which included leap years?
In: 6494
Ancient civilizations didn’t have leap years included.
Ancient calendars like the first Roman calendar didn’t much care about being precise, it only had 304 days in it and the ruler added extra days as holidays whenever they felt like it to make up for rest of the year. Is it summer but calendar is already October? Just add a bunch of holidays to sync back up.
Republic calendar already had leap years, but they didn’t count it the same, the error was too much. We didn’t get current Gregorian calendar until 1582. When the switch happened after centuries of calendar drift, 10 days were lost. Next date from October 4 1582 was October 15, the days between did not happen. Unless you were British, then you kept using Julian calendar until 1752 when you lost 11 days.
Ancient doesn’t mean stupid. Ancients were every bit as intelligent as moderns, capable of observation, critical thinking, drawing conclusions and projecting logic. And just like moderns, some were as smart as dirt.
Unlike today, the cycles of the sun, moon and stars were critical to harvest and survival. When one’s life depends on it, one concentrates hard.
A day is pretty easy to figure out, scratch a mark for each one. The position of the sun is also easy to figure out, scratch a mark on a rock. in a year or so, you can interpolate that a year is 365 days. Do it for another year to check your work.
Leap years take more than a year or two to figure out, after a few cycles you realize that an extra day keeps sneaking in. If you have a society which keeps records (scratches on rocks), and a class to maintain and interpret (shamans perhaps), then over a century or so, one can begin to track and interpret the anomalies. Moderns could do the same thing, except we are normally distracted by angry birds and tik-toks.
Fortunately we have a class of folks who specialize in observations, recordings, interpretations of data and projections of logic. Those are scientists, mathematicians, librarians, engineers, doctors, etc.
There are various ways they did it, but let’s go for one of the simplest: A stick.
Stick it upright in the ground. When the sun is highest, record where the shadow ends. Repeat all year, and you can tell when the longest and shortest days of the year are. Measure from one shortest day to the next and you have a year.
Repeat for a few years, and you’ll realize it’s around about 365 days. You probably want something more sturdy like an obelisk, though.
The more advanced technology after that is sundials, which can start to tell the time roughly. Earliest one we know that is around 1500 BCE.
It’s important to also remember that the calendar is one of the most critical pieces of technology for agriculture. When to sow, when to harvest, how large your reserves need to be, when to prepare for flooding, when to store water. All of those are centered around the calendar. So over thousands of years it makes sense that people would invest the time into documenting and studying it. Because it is so critical to survival
Fine details like leap years happened a lot later though.
Any time you have a question along the lines of “How did ancient peoples know…/figure out…/discover…”
The answer is always the same: they were observant.
45 BC lol
They’ve found land calendars dating to the Neolithic.
There was no TV during the last ice age so people had to do anything at night and that was watch the sky.
45 BC is not really that ancient – the last year of Julius Caesar’s life. The period known as classic antiquity. We are closer in time to Julius Caesar (100 – 44 BCE) than Caesar was to the first Egyptian dynasties (~3000 BCE).
Keep in mind that ancient humans were just as intelligent as modern humans – they developed the foundations of math, writing systems, structural engineering, understood agriculture, basic metallurgy, pottery/ceramics, etc. all of which they bootstrap without the benefit of widespread, efficient knowledge transfer (literacy, common education, etc.).
Since many things of very high importance to ancient people were dependent on seasons they learned over thousands of years to observe the sun, moon, planets and stars, the length of days, etc. and developed developed instruments to track these important cycles. There is evidence of early calendars going back to the neolithic (10,000 – 4500 BCE) – numerous monoliths, stones or structures that were used to track the solar year and/or lunar month. The Sumerians (~ 2000 BCE) had a solar year of 365 days with 12 months. Leap years were accounted for by periodically inserting days or months.
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