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Question: Let's say I don't believe the world is round. How can one prove the world is round to me?
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Timothy Todd, Geologist, writer (transitionstofreedom.com), traveler
Answered May 12, 2017

There are some great answers here, and another one is probably not necessary. But I had an exchange with some flat earthers that shifted my perspective on their thought processes (or the lack of them).

Anyone that’s ever interacted with an actual FE adherent knows that they will reject all evidence that the earth is any shape other than flat. Depending on your disposition, it can be pretty entertaining to watch them struggle through the dissonance that arises when they attempt to reconcile their unshakable faith in their world view with facts that contradict it.

I used to live in Kailua-Kona on the Big Island of Hawaii. We had a house there that faced west with a spectacular view of the coastline and the Pacific. It was about 1200 feet above sea level.

One evening, near sunset, I was at home perusing the silly musings of a group of FE adherents on a public forum. My wife happened to be in town near the beach about the time the sun set. I called her just as it was setting to ask her to tell me the exact moment that the tip of the sun sank below the horizon. At the moment that she confirmed her observation of the sun’s disappearance, I could still see a portion of the sun above the horizon from my elevated vantage point. I then marked the time that I observed the sun disappear below the horizon.

The distance to the horizon on the ocean can be estimated by using d = 3.57 * √h where d is the distance to the horizon in kilometers and h is the elevation of the observer in meters. Using 5 meters for my wife’s elevation (she was not directly on the beach) and 400 meters for mine, I estimated that the distance to the visible horizon for her was about 8 kilometers, while from my location it was about 70 kilometers. Since she was about 5 kilometers west of me, I added that to her 8 kilometers, making my visible horizon about 57 kilometers further west than my wife’s.

The earth’s rotational speed at any latitude can be estimated by multiplying the cosine of latitude in degrees by 1670 kilometers per hour (the rotational speed at the equator). In our case, we were at about 19.6 degrees north latitude, so our rotational speed was around 1,570 kilometers per hour, or about 26 kilometers per minute. That meant that the sun should disappear under the horizon about 2 minutes later for me than for her, which is exactly what we observed.

I shared our observations and the associated calculations with the FE cultists on the forum that I’d been reading. You won’t be surprised to learn that I was unable to claim a single convert. Instead, I was ridiculed, insulted, and mocked, but not on the basis of any reasoned rebuttal. The most common response was some variation on the theme that I was lying. I was eventually invited to leave the forum and asked not to engage in further discussion.

Yes, I know that it was a foolish waste of my time, but I did come away with some interesting insights into human nature and the FE cult mindset. Reason and evidence are not the ingredients that have led them to their understanding of reality, so reason and evidence will never be part of the solution that will help them to accept the world as it is rather than as they want it to be.

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Here's an answer for you:
.
.
Question: Let's say I don't believe the world is round. How can one prove the world is round to me?
.
Timothy Todd, Geologist, writer (transitionstofreedom.com), traveler
Answered May 12, 2017

There are some great answers here, and another one is probably not necessary. But I had an exchange with some flat earthers that shifted my perspective on their thought processes (or the lack of them).

Anyone that’s ever interacted with an actual FE adherent knows that they will reject all evidence that the earth is any shape other than flat. Depending on your disposition, it can be pretty entertaining to watch them struggle through the dissonance that arises when they attempt to reconcile their unshakable faith in their world view with facts that contradict it.

I used to live in Kailua-Kona on the Big Island of Hawaii. We had a house there that faced west with a spectacular view of the coastline and the Pacific. It was about 1200 feet above sea level.

One evening, near sunset, I was at home perusing the silly musings of a group of FE adherents on a public forum. My wife happened to be in town near the beach about the time the sun set. I called her just as it was setting to ask her to tell me the exact moment that the tip of the sun sank below the horizon. At the moment that she confirmed her observation of the sun’s disappearance, I could still see a portion of the sun above the horizon from my elevated vantage point. I then marked the time that I observed the sun disappear below the horizon.

The distance to the horizon on the ocean can be estimated by using d = 3.57 * √h where d is the distance to the horizon in kilometers and h is the elevation of the observer in meters. Using 5 meters for my wife’s elevation (she was not directly on the beach) and 400 meters for mine, I estimated that the distance to the visible horizon for her was about 8 kilometers, while from my location it was about 70 kilometers. Since she was about 5 kilometers west of me, I added that to her 8 kilometers, making my visible horizon about 57 kilometers further west than my wife’s.

The earth’s rotational speed at any latitude can be estimated by multiplying the cosine of latitude in degrees by 1670 kilometers per hour (the rotational speed at the equator). In our case, we were at about 19.6 degrees north latitude, so our rotational speed was around 1,570 kilometers per hour, or about 26 kilometers per minute. That meant that the sun should disappear under the horizon about 2 minutes later for me than for her, which is exactly what we observed.

I shared our observations and the associated calculations with the FE cultists on the forum that I’d been reading. You won’t be surprised to learn that I was unable to claim a single convert. Instead, I was ridiculed, insulted, and mocked, but not on the basis of any reasoned rebuttal. The most common response was some variation on the theme that I was lying. I was eventually invited to leave the forum and asked not to engage in further discussion.

Yes, I know that it was a foolish waste of my time, but I did come away with some interesting insights into human nature and the FE cult mindset. Reason and evidence are not the ingredients that have led them to their understanding of reality, so reason and evidence will never be part of the solution that will help them to accept the world as it is rather than as they want it to be.

This argument is flawed for so many reasons.  First: earth doesn't rotate.  Scripture says earth is fixed, on a foundation, and movement of the earth is condemned by the Church.  Second: many globe geocentric theorists do not think the earth rotates either, so this guy is attempting to make a case for the heliocentric model, another specifically condemned proposition.  Why promote what is already condemned?  As if this guy's observation of sun setting 2 minutes apart from his wife is scientific?  This doesn't even take into account the direction of the sun's trajectory in relation to persons on the ground which could account for that or even more time difference in sun setting.  Third: Flat earthers are no more rude to globers than globers are to fe'rs, so getting ran out on a rail off that forum was the result of inadequate data for his observational conclusion.     

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Keep in mind who is hosting this so-called International Flat-Earthdom Syndromers' Conference.