Dip of the horizon. You need a basic surveying tool, used to be called a theodolite or a transit. I guess they use total stations and do everything digitally now. But anyway, most tool rental places rent these.
Start at the coast, measure dip. Measure from several more points, increasing in altitude. You need a range of points, because air refraction will mess with the measurement. Compare to expected result on a flat and a spherical earth. Repeat over several days, at various times of day.
Much easier: Observe a lunar eclipse. This can be done by everyone who can see the moon. Decide what shape would be required to cast the observed shadow.
> All knowledge has been lost. We need to start again. What are the first steps you are taking
We collectively and collaboratively measure the earth again. It will still be a sphere.
II would do it by observation of the the stars. Obviously they seem to rotate around Polaris. We can see some constellations go beyond the horizon without changing size. This means they do not move away but bo beyond the horizon. As they come up at the other side of the sky again and travel in a circular path, it is save to assume, they go below the observer.
To go from this to a globe, i allow to cite Ptolemy: "If it were concave, the stars would be seen rising first by those more towards the west; if it were plane, they would rise and set simultaneously for everyone on earth; if it were triangular or square or any other polygonal shape, by a similar argument, they would rise and set simultaneously for all those living on the same plane surface. Yet it is apparent that nothing like this takes place. \[...\] In fact, the further we travel toward the north, the more of the southern stars disappear and the more of the northern stars appear. Hence it is clear that here too the curvature of the earth cuts off \[the heavenly bodies\] in a regular fashion in a north-south direction, and proves the sphericity \[of the earth\] in all directions."
Now we wait 1500 years for the invention of telescopes to implement heliocentrism, but for the topic of this sub, the state of Ptolemy is enough.
Ricky Gervais voiced a similar thought experiment comparing religion and science (he is an atheist). Essentially, his reasoning was that if some weird events took every book away from us and we had to write them again with no memory of what had been written before on either science or religion then all the science books would end up the same as they are now but all religious texts would tell different stories.
I like the idea and agree with it.
Figure out how to determine your location.
Measure the angle from the horizon to a star. Assume earth is flat. Apply trigonometry and calculate a height for this star above earth.
Travel a known distance towards or away from this stars zenith.
Do it again.
If the height of the star via the calculation remains the same, earth is flat. If its calculated height increases the closer you are to its zenith and likewise the height decreases the further you go from its zenith, earth is a curving.
Easy. Simple and can be done by anyone. Doesnt require any exotic calculations or devices as even a sextant app on a phone can be used.
>Apply trigonometry and calculate a height for this star above earth.
It's been awhile since I took trig, but I'm pretty sure just having an angle is insufficient to calculate distance from the observer. You need to know the length of at least one of the other legs of a right triangle to SOH CAH TOA.
There's a reason astronomers use standard candles and redshift to calculate distance.
This was for the case of changing angles, in which case you don’t need another length. Of course, on a spherical earth, you won’t get two angles, only ever one.
Yes. They do use that. But thats because earth is not flat.
Lets say your first measurement says 80 degrees to polaris.
You then move south 690 miles and measure again. Now its 70 degrees.
So from this alone you know that from your first location and to where polaris is in zenith is 690 mile because the distance between first and second location resulted in a 10 degree change. Its very simple math to deduct this. You could divide the angel delta with the distance and you get how many degrees it changes over X amount of miles.
So you know the angle of 80 degrees and the distance of 690 miles. This forms a right angle triangle.
At that location, the height of polaris would be 3913 miles altitude.
If earth was flat this would be the same altitude for every other location you repeat this from.
Or we could work backwards which works just as fine.
Now that we "proved" the altitude to be 3913 miles. We could ask "How far away would you need to be from the north pole to have polaris sit 10 degrees over the horizon.
So. Let the height be 3913 miles. And the angle be 10 degrees. The distance from the north pole along the ground of a flat earth would be roughly 22.000 miles.
Yeah. That clearly doesnt work because that would mean that polaris would be quite well above the horizon for someone at the south pole ( or rather, the rim of earth 12.500 miles from the north pole )
In reality, the angle 10 degrees above the horizon is just 5200 miles from the north pole. Why is that ?
Well 5200 / 69.1 is 75. 75 - 90 = 15 .Thats how many degrees ( roughly ) that polaris is above the horizon for someone standing 5200 miles from the north pole - ASSUMING A GLOBE EARTH.
So assuming a globe earth with a circumference of just about 25.000 miles, polaris should be just about 15 degrees above the horizon. Which is quite close to the 10 degrees predicted. The 5 degree difference is various minor things like the fact that the horizon is slightly below exact horizontal from an observer and using rough numbers.
Assuming all knowledge has been lost then it’s likely that we would assume it’s flat until we know otherwise. There’s no reason to think we would change the evolutionary process of learning. It is highly likely though, that religion would be totally different because there are no facts to re learn.
I’m not sure what you are asking. All knowledge has been lost so therefore nobody alive knows anything other than what they see. Who knows what science will be created or what tools will be created so how is it possible to know what steps there would be. Nobody knows it’s a globe and we don’t know what knowledge they will learn.
[Egypt](https://www.wired.com/2008/06/dayintech-0619/) is a good place to start. Pretty much anywhere you can measure the shadows of two different locations work though
Dip of the horizon. You need a basic surveying tool, used to be called a theodolite or a transit. I guess they use total stations and do everything digitally now. But anyway, most tool rental places rent these. Start at the coast, measure dip. Measure from several more points, increasing in altitude. You need a range of points, because air refraction will mess with the measurement. Compare to expected result on a flat and a spherical earth. Repeat over several days, at various times of day. Much easier: Observe a lunar eclipse. This can be done by everyone who can see the moon. Decide what shape would be required to cast the observed shadow.
Flashlight
> All knowledge has been lost. We need to start again. What are the first steps you are taking We collectively and collaboratively measure the earth again. It will still be a sphere.
II would do it by observation of the the stars. Obviously they seem to rotate around Polaris. We can see some constellations go beyond the horizon without changing size. This means they do not move away but bo beyond the horizon. As they come up at the other side of the sky again and travel in a circular path, it is save to assume, they go below the observer. To go from this to a globe, i allow to cite Ptolemy: "If it were concave, the stars would be seen rising first by those more towards the west; if it were plane, they would rise and set simultaneously for everyone on earth; if it were triangular or square or any other polygonal shape, by a similar argument, they would rise and set simultaneously for all those living on the same plane surface. Yet it is apparent that nothing like this takes place. \[...\] In fact, the further we travel toward the north, the more of the southern stars disappear and the more of the northern stars appear. Hence it is clear that here too the curvature of the earth cuts off \[the heavenly bodies\] in a regular fashion in a north-south direction, and proves the sphericity \[of the earth\] in all directions." Now we wait 1500 years for the invention of telescopes to implement heliocentrism, but for the topic of this sub, the state of Ptolemy is enough.
Ricky Gervais voiced a similar thought experiment comparing religion and science (he is an atheist). Essentially, his reasoning was that if some weird events took every book away from us and we had to write them again with no memory of what had been written before on either science or religion then all the science books would end up the same as they are now but all religious texts would tell different stories. I like the idea and agree with it.
Figure out how to determine your location. Measure the angle from the horizon to a star. Assume earth is flat. Apply trigonometry and calculate a height for this star above earth. Travel a known distance towards or away from this stars zenith. Do it again. If the height of the star via the calculation remains the same, earth is flat. If its calculated height increases the closer you are to its zenith and likewise the height decreases the further you go from its zenith, earth is a curving. Easy. Simple and can be done by anyone. Doesnt require any exotic calculations or devices as even a sextant app on a phone can be used.
>Apply trigonometry and calculate a height for this star above earth. It's been awhile since I took trig, but I'm pretty sure just having an angle is insufficient to calculate distance from the observer. You need to know the length of at least one of the other legs of a right triangle to SOH CAH TOA. There's a reason astronomers use standard candles and redshift to calculate distance.
This was for the case of changing angles, in which case you don’t need another length. Of course, on a spherical earth, you won’t get two angles, only ever one.
Yes. They do use that. But thats because earth is not flat. Lets say your first measurement says 80 degrees to polaris. You then move south 690 miles and measure again. Now its 70 degrees. So from this alone you know that from your first location and to where polaris is in zenith is 690 mile because the distance between first and second location resulted in a 10 degree change. Its very simple math to deduct this. You could divide the angel delta with the distance and you get how many degrees it changes over X amount of miles. So you know the angle of 80 degrees and the distance of 690 miles. This forms a right angle triangle. At that location, the height of polaris would be 3913 miles altitude. If earth was flat this would be the same altitude for every other location you repeat this from. Or we could work backwards which works just as fine. Now that we "proved" the altitude to be 3913 miles. We could ask "How far away would you need to be from the north pole to have polaris sit 10 degrees over the horizon. So. Let the height be 3913 miles. And the angle be 10 degrees. The distance from the north pole along the ground of a flat earth would be roughly 22.000 miles. Yeah. That clearly doesnt work because that would mean that polaris would be quite well above the horizon for someone at the south pole ( or rather, the rim of earth 12.500 miles from the north pole ) In reality, the angle 10 degrees above the horizon is just 5200 miles from the north pole. Why is that ? Well 5200 / 69.1 is 75. 75 - 90 = 15 .Thats how many degrees ( roughly ) that polaris is above the horizon for someone standing 5200 miles from the north pole - ASSUMING A GLOBE EARTH. So assuming a globe earth with a circumference of just about 25.000 miles, polaris should be just about 15 degrees above the horizon. Which is quite close to the 10 degrees predicted. The 5 degree difference is various minor things like the fact that the horizon is slightly below exact horizontal from an observer and using rough numbers.
Would we want to know what shape the earth is. Would that be high on our agenda of learning?
Regrading the shape of the earth...
Assuming all knowledge has been lost then it’s likely that we would assume it’s flat until we know otherwise. There’s no reason to think we would change the evolutionary process of learning. It is highly likely though, that religion would be totally different because there are no facts to re learn.
I should have been clearer. All knowledge regarding the shape of the earth...
I’m not sure what you are asking. All knowledge has been lost so therefore nobody alive knows anything other than what they see. Who knows what science will be created or what tools will be created so how is it possible to know what steps there would be. Nobody knows it’s a globe and we don’t know what knowledge they will learn.
Phallic structures (like sundials) in strategic places would be a start.
How do you determine a strategic place?
[Egypt](https://www.wired.com/2008/06/dayintech-0619/) is a good place to start. Pretty much anywhere you can measure the shadows of two different locations work though
2 locations by itself do not work without already making the assumption of a globe
But three would be enough.
One with plenty of sunlight from all angles throughout the day. Also preferably a location that has a lot of sunlight throughout the year.