How to convince a flat earther that the Earth is spherical?

Actually, those who would have to refute the sphericity of the Earth are the flat earthers, because the current evidence is that the Earth is round.

Humans have already explored and measured the planet in a thousand ways, there are daily plane flights between all points on the map and the distances are well known.

There are about 5,000 satellites that orbit the Earth and take daily photos showing that it is round, but many flat earthers claim that all these photos are fake.

In other words, this discussion ceases to be a scientific question if there is no confidence in the evidence proposed by others.

In my opinion, it is as if we all have an orange in front of us and the flat earthers say that what you see is not credible and continue to affirm that the orange is actually flat.

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You can't convince a flat earther and that should worry you

The Earth has been known to be spherical for more than 2,000 years, long before the satellites and the first circumnavigation of the world.

There is much mathematical evidence that the Greeks calculated with their knowledge of geometry and navigation.

However, to answer your question I have looked for simple arguments, easily verifiable in daily life and that would not fit on a flat Earth.

There are many, but I will tell you five:

First:

we all know that the higher we go, the further we can see.

If the Earth were flat, this would not be the case.

On a flat Earth you would have to see to the end of the Earth in any place without relief, like the sea, for example.

From Galicia you should see America with a sufficiently powerful telescope, but it is not possible due to the curvature of the Earth's surface.

As this has been known since ancient times, the lighthouses are placed on top of a tower so that they are visible from a greater distance.

And vice versa, if you are in a port and you see a ship arrive, first you see the highest part of the ship appear, the mast;

then the sails and finally the hull.

Second:

the times of sunrise and sunset are different in every part of the world.

If you think about it, this would not be the case on a flat Earth either.

Moreover, and in relation to the previous point, the time at which the sun sets in each place also depends on the height from which you are looking at the horizon.

Muslims have studied this very well.

Tables with sunset times are available online for almost every place in the world to know exactly when you can break your fast during Ramadan.

If you look for those tables for Dubai, they warn you at the beginning that in the Burj Khalifa building, which is 828 meters high and is the tallest in the world, the sun sets three minutes later on the highest floor than on the lowest floor. short.

This would not happen on a flat planet either.

Third:

the water from the sump.

On a flat, non-rotating Earth the water should fall into the sink directly towards the center, everywhere equally, but it doesn't.

When you empty a sink (better if it is a large round pool) a whirlpool is formed by the Coriolis effect that can only be explained by the rotation of the Earth.

Flat earthers could say that a flat Earth could also rotate on its axis and that this could generate a whirlpool like the one we see.

The problem is that the eddies of the pools rotate in the opposite direction in one hemisphere and the other (also the storms and anticyclones).

For that, on a flat Earth we would need two opposing rotating poles that would each affect half of the Earth.

Fourth:

the movement of the night sky.

This argument is similar to the previous one.

In the northern hemisphere the entire night sky revolves around the Polaris in the counterclockwise direction, while in the southern hemisphere everything revolves around the Southern Cross in the opposite direction.

For that to be the case on a flat Earth, you would have to have two celestial spheres, one for each hemisphere, rotating in opposite directions.

Fifth:

the duration of long trips is different if you travel east or west.

This fact has no explanation on a flat Earth.

I am going to give two very different examples, but both have to do with a spherical Earth that rotates on itself.

A fairly everyday example is that the flight from Madrid to New York is longer than the one from New York to Madrid, and this is because the return flight is helped by the jet stream that travels eastward and has its origin in the Earth's rotation.

The other argument, somewhat further away but very curious, is the paradox of the circumnavigator.

This paradox is that if you go around the world, it doesn't take as long if you go west as if you go east.

In this case, no matter how long it takes you to go all the way around, if you travel east you win a day,

like Phileas Fogg in Jules Verne's novel, while if you travel west you lose it, as happened to Elcano and his crew at the end of the first circumnavigation.

This paradox is impossible to explain on a flat Earth where the sun rises at the same time for everyone and everyone shares the same calendar date.

María Belén Muñoz García

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