How did mankind know the earth was round 5000 years ago?

Question

I've read that the builders of the Great Pyramid knew the earth was round because the dimensions of it are based on the exact size of the earth.

Is there a way to look at the stars or something and know the size of the earth?

And how come they knew something 5000 years ago we just figured out 500 years ago?

I have my ideas of how but I'd like to hear how you think they did it, also how did ancient people know exact north and south?

Complicated mathematical inferences can be made by studying the geometry of the Great Pyramid, one of which suggests that the builders knew the circumference of the earth, and also knew that it was not a perfect round shape. Tiny discrepancies in the measurements at the base of the pyramid that were originally thought to be errors on the part of the builders are now thought to be purposeful, and geometrically the numbers accurately depict the circumference and shape of the earth, with the errors accurately corresponding to the flattening of the earth at the poles.

http://www.mysticalblaze.com/PlacesPyramidsDimensions.htm

Answer 1

If you watch a lunar eclipse, you can see the Moon entering the shadow of the Earth, which is a circle on the sky. If they could figure out the phases of the Moon and the reason for it, they could figure out that the Earth was round.

Answer 2

They did know that the world was round 5000 years ago. The idea that Columbus set out to prove that the world was round was myth. Pretty much everyone new that by the 15th century when Columbus made his voyages. You can tell for a few reasons such as, the earths shadow on the moon during a lunar eclipse is round. And ships traveling out past the horizon appeared to sink down from the shore their mast being the last thing to disappear.

The size of the earth was in question though. Columbus estimate the earth only had about 1/4 the circumference it actually had, that's why he thought he could get to India in just a few weeks.

And I do not believe that there is any relation between the dimensions of the pyramids and the size of the earth. I have heard that the orientation of the pyramids was aligned with different stars but nothing requiring them to know the size of the earth.

There is a good book called "A Short History of Nearly Everything" by Bill Bryson and the first 1/3 of the book roughly is concerned with the history of scientists and mathematicians trying to determine the size of the earth.

Answer 3

Hi there. I don't know how or if the builders of the pyramids understood the dimensions of the Earth, but it certainly wasn't beyond their means - technically speaking.

Whether or not they actually had the knowledge of geometry to use the approach I'm about to relate, is another question, and one I won't address.

A Greek savant named Eratosthenes figured out the circumference of the Earth a little over two thousand years ago. He was cheif librarian at Alexandria at the time.

He used geometry and geography to deduce the size of the Earth (by making observations of shadows at noon, over two points on the Earth's surface a known distance apart from each other - see sources 1 & 2 below.)

As for how ancient folks determined the cardinal directions, check out link #3 below - turns out there are a number of ways to accomplish this. While I knew that Polaris hasn't always been the "North Star", it so happens that another star would have fufilled that role for the Egyptians - "Thuban" ...

Answer 4

Astronomers calculated the approximate size of the earth before the birth of Christ, and understood that it was round. Thus it is incorrect to say that scientists in medieval times did not know this. Some even postulated a heliocentric (sun-centered) universe. The mathematical models they used were sufficient to the task, but their measuring instruments were not adequate to calculate the size of the sun. Their estimate of the earth's size was pretty close.
A huge amount of this science was lost in the fire or fires that destroyed the great library and museum at Alexandria, Egypt, between the first century BC and the fourth century AD.
So, it seems to me possible that ancient Egyptians could have calculated the approximate size of the earth. Their flat geography and clear skies (even their water came from the Nile, not from rainfall) made a great location for the study of astronomy, and they were masters at it.

Answer 5

There was a man in ancient Greece – I forget his name – who noticed that a shadow cast by a tower in one town at local noon differed from the shadow cast by a tower in another town several hundred miles away. He and a colleague took measurements of the shadows of these towers and, using a little basic trigonometry, determined not only that the Earth was round, but also determined its circumference to an astonishing degree of accuracy, given then-current technology.

As for where all this knowledge went during the medieval period, the fall of Rome pretty much halted all scientific progress as feudal lords fought for more and more power, and peasants were more concerned with mere survival.

Ancient navigation was accomplished with stars, most notably Polaris, the "North Star".

Answer 6

There is are any number of pieces of evidence that ancient man could have used to determine that the Earth was round.

One was looking at objects like the sun and moon, noting their roundness, and assuming that the Earth might also be round. It's not really evidence, but it is logical.

Another is the appearance of objects on the horizon. A ship appearing on the horizon appears mast first because it is coming over the curvature of the Earth. People up higher see distant objects sooner because they can see a greater section of the curved Earth. Ancient peoples who relied on line of sight navigation and fishing fleets for food and military might would have been well aware of these phenomena.

Over the course of the year and even the night, astronomical bodies move about the night sky in a cyclical, round pattern. Again, it would be logical to assume that the Earth also follows this round pattern.

As to the pyramids being built according to the exact dimensions of the Earth, the reason it's difficult to believe the Ancient Egyptians were capable of such a feat is probably because they weren't. The pyramids aren't really built to the dimensions of the Earth. The pyramids are all different sizes, and differed in proportions of construction as well. There may well be some that just happen to be a certain proportion of the size of the Earth, but that's probably just coincidence - like the fact that it's 1:37 pm right now, I received 37 cents change for my lunch today, and 37 days ago I ate 37 M&Ms at one sitting. There's no actual significance to the numbers.

As to north and south, magnetic rocks, known as lodestones were used in navigation and mystical rites since before civilization. These naturally occurring iron rich minerals like magnetite will swivel on their own to point due north - especially if hung from a string or the like. The unexplained and obviously miraculous ability of these rocks would have had a powerful impact on observers, and its not hard to see why religious icons might have been built according to the orientations seen in the lodestones.

Answer 7

Good question. I'm not sure how exactly they figured it out. But a lot of people knew stuff way way before we (westerners) ever discovered them. The ancient Indians (India) knew all about the atom and the earth's rotation/revolution around the time Jesus was born. 1500 years before Galileo and Copernicus came on the scene!

Answer 8

Eri nailed it. Watching the eclipses told them.