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How was the size of Earth first measured? (2015)

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Re: How was the size of Earth first measured? (2015)

#81

Post by dghughes »

extragood wrote: post #50
mcdonje wrote: post #6

Classic Carl Sagan clip relaying this story: https://m.youtube.com/watch?v=8hZl3arO7SY

This article had one detail that was not included in the video that had always bugged me. Carl says "how could it be .. that at the same instant there was no shadow at Syene and a very substantial shadow at Alexandria". That seemingly requires coordination between 2 people across a vast distance and accurate time measurement. I rationalized that it could be accomplished with people at each location, each with a sundi…

>I rationalized that it could be accomplished with people at each location, each with a sundial, making records of shadow length, and later comparing their measurements, but it still seemed like a messy explanation.

I'd like to know how ancient people figured out how to make a sundial. They need to point the stick called a gnomon north if they're in the northern hemisphere or south if in the south. Not just pointed an old way it needs to be tilted at the angle according to their latitude it's not just a vertical stick in the ground.

Re: How was the size of Earth first measured? (2015)

#83

Post by ljlolel »

bryan0 wrote: post #11

Terrence Tao has an old excellent presentation on the “cosmic ladder” which shows how from this measurement you can build up to measure the largest distances in the visible universe: https://terrytao.files.wordpress.com/2010/10/cosmic-distance...

This has changed my life thank you

Re: How was the size of Earth first measured? (2015)

#84

Post by kemotep »

jan_Sate wrote: post #82

This estimation method would only work under the assumption that earth is a spherical. Now that we do know that it's a sphere. But how could you figure that out back in 2000 years ago?

That’s the entire thing! He read an account of a city so many miles away from where he was that on a specific day of the year had no shadows at noon. On that day in his city, shadows still were cast. If there was no discrepancies in the shadows that would make sense for a flat earth. But the discrepancy made him determine it had to be sphere and then he went out and calculated the circumference.

Re: How was the size of Earth first measured? (2015)

#85

Post by taneq »

jan_Sate wrote: post #82

This estimation method would only work under the assumption that earth is a spherical. Now that we do know that it's a sphere. But how could you figure that out back in 2000 years ago?

Because spheres are the best Platonic solid and so Earth must be a sphere, naturally.

Re: How was the size of Earth first measured? (2015)

#87

Post by HWR_14 »

taneq wrote: post #85
jan_Sate wrote: post #82

This estimation method would only work under the assumption that earth is a spherical. Now that we do know that it's a sphere. But how could you figure that out back in 2000 years ago?

Because spheres are the best Platonic solid and so Earth must be a sphere, naturally.

Spheres aren't Platonic solids.

Re: How was the size of Earth first measured? (2015)

#88

Post by postmodest »

StackOverlord wrote: post #76
ahazred8ta wrote: post #49

Earlier quoted context omitted.

There are crackpots who think the builders of the Great Pyramid knew the size of the Earth. https://www.hallofmaat.com/numerology/a-critique-of-graham-h...

You can get to the absolute dimensions of the pyramid from the crackpot equations though: https://pasteboard.co/cIMzn8KktEZy.png https://tobeornottobe.org/the-great-pyramid-intro/math-const... https://pastebin.com/TsUtcWAa I just found a great recap on this topic that also fits nicely with the points your link brings up, shedding a better light on the number 43,200 in other cultures (the scaling factor between the py…

I'm not convinced until the pyramids encode the Meter and the Kilogram and Mole. ...in Hex.

Re: How was the size of Earth first measured? (2015)

#89

Post by metacritic12 »

demondemidi wrote: post #86

How did Eratosthenese synchronize the measurements? That seems like the biggest challenge: sync'ing two clocks and transporting one to a place 500 miles away without losing time? 2000 years ago?

He timed solar noon and travelled due north / south to avoid the time zone problem.

Re: How was the size of Earth first measured? (2015)

#90

Post by rootw0rm »

postmodest wrote: post #88
StackOverlord wrote: post #76

Earlier quoted context omitted.

You can get to the absolute dimensions of the pyramid from the crackpot equations though: https://pasteboard.co/cIMzn8KktEZy.png https://tobeornottobe.org/the-great-pyramid-intro/math-const... https://pastebin.com/TsUtcWAa I just found a great recap on this topic that also fits nicely with the points your link brings up, shedding a better light on the number 43,200 in other cultures (the scaling factor between the py…

I'm not convinced until the pyramids encode the Meter and the Kilogram and Mole. ...in Hex.

make enough measurements and you can probably find those "encoded" there, too
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