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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)

#21

Post by kwhitefoot »

xattt wrote: post #8

Given the large distance between the cities, how did they communicate to confirm that the sun was indeed overhead at particular time and date?

You don't need to communicate in real time. You just need to agree on which date to do the measurement and that is determined by reference to the stars. Priests had been maintaining the calendar already for quite some time. Then you just wait for the sun to reach the zenith, noon. Now you can measure the angle of the sun from the vertical then it's relatively simple trigonometry to calculate the circumference.

See https://en.wikipedia.org/wiki/Earth%27s_circumference

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

#24

Post by grog454 »

bedobi wrote: post #20

I always struggled (and still struggle) with math. A couple of years ago, randomly browsing YouTube, I came across this home made video asking how they figured out the distance to the moon before modern technology. The host starts out small scale showing he can calculate the distance to things in his back yard using trigonometry and then scales it up to the moon. My mind was blown, because no one ever told me that. I…

I had a similar experience earlier in my education. "Learning" sine and cosine was nothing compared to understanding it well enough to use in a 2d game. I went from struggling with standard algebra classes to getting 5s on AP Calculus BC and Physics.

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

#27

Post by 082349872349872 »

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...

Wow, TIL the reason Aristarchus' contemporaries didn't accept his heliocentric model...

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

#28

Post by mhuffman »

bedobi wrote: post #20

I always struggled (and still struggle) with math. A couple of years ago, randomly browsing YouTube, I came across this home made video asking how they figured out the distance to the moon before modern technology. The host starts out small scale showing he can calculate the distance to things in his back yard using trigonometry and then scales it up to the moon. My mind was blown, because no one ever told me that. I…

Which video?
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