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?

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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?

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Anonymous 0 Comments

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.

Anonymous 0 Comments

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.

Anonymous 0 Comments

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.

Anonymous 0 Comments

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.

Anonymous 0 Comments

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.

Anonymous 0 Comments

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.

Anonymous 0 Comments

You don’t need to know that the Earth orbits the Sun to create a calendar. All you need is the length of the year, and you can get that by observing the sun and stars.

You can tell if your calendar is drifting out of sync with the seasons, again using observations of the stars.

Anonymous 0 Comments

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.

Anonymous 0 Comments

Ancient peoples were as intelligent as we are and had lots of tools. For example, they could count the days of the year, and could measure the height of the sun in the sky using things like the length of the shadow cast by a pole or tower, so they could see it was about 360+ days from when the shadow was longest, until the next time it got that long and they could see that it was always summer when the shadow was shortest and winter when it was longest, so clearly the seasons were linked to how high the sun was in the sky, and to how many days had passed since the previous winter. And this was very useful information as it helped them figure out when to plant, or when to hunt migrating herds or seasonal wild food plants and so on.

So over many years of observation and record keeping they would have figured out that the length of the year was 365 days, but you had to add a day now and then to keep it working.

Most ancient civilizations did not know the earth orbited around the sun. However some ancient thinkers might have suspected it. We don’t know who first came up with the idea, but Copernicus pretty much proved it, so he gets the main credit. As well we don’t know who first suspected the earth was a sphere but it’s possible it was thought of by some ancient thinkers long before the ones we credit. The clues were there, for example ships or mountains seeming to drop below the horizon, the farther away they were.

And all this would have happened long before 45 BC – maybe thousands of years earlier. Stonehenge might have been started around 3000 BC and it contains a fair amount of advanced astronomical features, that would have been based on knowledge people might have been developing from even much earlier.

Edit: Okay people, Galileo, Newton and probably others provided proof of Copernicus’s model.

Anonymous 0 Comments

The Sumerians figured out the length of the year a lot earlier than 45BC. The first observation you might make if you were to do this yourself is that seasons follow a regular pattern and that pattern coincides with celestial observations. In the northern hemisphere, the sun rises and sets farther to the south in the winter than it does in the summer. Also, certain stars and constellations are only visible during certain times of the year.

Something you might try to do is count the number of days between the most southerly sunrises. All you need to do that is three sticks, some way of tallying numbers (a jar and a bunch of pebbles will do), and a whole lot of patience. You don’t know what day it is because calendars don’t exist, but you know it’s autumn because it’s getting colder and the leaves are changing, from that you know the sunrise should be moving south. You find a spot that has a good, unobstructed view, maybe a hill top overlooking the sea and you drive one of your sticks into the ground. The next morning, you get up at dawn and see where the sun rises. You take your second stick and drive it into the ground so that the two sticks and the sun form a straight line. The next day you do the same thing, drive the third stick into the ground and note that it is to the right of the second. Keep doing that every morning, leapfrogging the second and third stick over one another until you get to a morning where the latest observation is to the left of the last. That is your reference for the start if the year, toss a pebble into the jar. Keep doing that every day and you’ll notice that some time during the summer, the sticks will change course again and you’ll have something like 180-200 pebbles in the jar. Keep going and once the sticks get back to where you started counting (you’ll know because they change direction again) you can count count the pebbles and there should be about 365 of them. Do that a couple more times and you can be sure of your results.

Another way you can check your work is by following a particular star, let’s use Sirius because it’s the brightest and close to an easily recognized constellation. Conveniently, the first night you would be able to see Sirius after the sun sets is close to the winter solstice. If you start putting pebbles in your jar each day after that and keep going until it becomes visible the next winter, you should also wind up with about 365 pebbles in your jar