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40 votes
Accepted

How did Eratosthenes know the Sun was very far away?

We do not know for sure what Eratosthenes read, but at his time this was a common knowledge. This can be inferred from the book of Archimedes, The sand reckoner (Archimedes was Eratosthenes' ...
Alexandre Eremenko's user avatar
16 votes

How did Eratosthenes know the Sun was very far away?

This is a long answer, explaining more or less step to step why the data available to Eratosthenes indicted that the Sun should be a vast distance from the Earth, thus makings its diverging rays ...
M.A. Golding's user avatar
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14 votes

How did Eratosthenes determine that Alexandria and Syene were on the same meridian?

We do not know. First, Syene and Alexandria are not on the same meridian, Alexandria is about 3° to the West, and second, Syene is not on the tropic (where the Sun is straight up on the summer ...
Conifold's user avatar
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11 votes
Accepted

When was it discovered that the Earth wasn't round?

Discarding the ungrounded speculations (for example, Columbus claimed that Earth has a "bulge"), scientific theories which predicted deviation of Earth's shape from the sphere were proposed in he late ...
Alexandre Eremenko's user avatar
11 votes

Why are there so few Iberian mathematicians in history?

Unlike North Africa and the Near East, the Iberian Peninsula missed out on the Hellenic influence that dominated classical mathematics; hence the lack of an Iberian Euclid. Compared to the Greeks, the ...
Uri Granta's user avatar
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10 votes

Why did Columbus think the Earth was much smaller than it is?

Answering the earlier version of the question first (on Columbus mistakes). There were two main sources of mistakes: exaggerating the size of Asia and underestimating the size of the Earth. Columbus ...
Alexandre Eremenko's user avatar
10 votes
Accepted

Why are there so few Iberian mathematicians in history?

As I was uncertain about the premise of this question—i.e., it looks as if there are fewer Spanish and Portuguese mathematicians than others—but without the numbers to prove it, I went in for some ...
gktscrk's user avatar
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10 votes
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How did cartographers of past centuries determine latitude and longitude?

The concepts of latitude and longitude were introduced in antiquity, and our principal source for that period are the surviving books by Ptolemy (Geography and Almagest). These notions were understood ...
Alexandre Eremenko's user avatar
8 votes

How did Eratosthenes determine that Alexandria and Syene were on the same meridian?

He may simply not have cared. A reasonably small distance along the east-west axis will only lead to a very small error in the distance along the north-south axis. E.g. an azimuth of 190° instead of ...
Jan's user avatar
  • 181
7 votes

Early geographically accurate drawings of Earth

Wikipedia has a good list of such maps. The first one for me that shows the continents roughly as we see today (Minus Antarctica) seems to be the Kunyu Wanguo Quantu 1602 map, included below, which is ...
PearsonArtPhoto's user avatar
6 votes

What is the origin of the four cardinal directions (North, East, South, and West)?

The origin is astronomical. North is the direction to the North Pole of the celestial sphere. (To the point about which the sky performs its daily rotation as seen from the Northern hemisphere). The ...
Alexandre Eremenko's user avatar
6 votes

How did Scott and Amundsen detect the South Pole?

I want to add to this answer some details about "measuring latitude". The instruments used are sextant (for measuring altitude of a star (or Sun or Moon) over the horizon, and chronometer ...
Alexandre Eremenko's user avatar
5 votes
Accepted

How did Scott and Amundsen detect the South Pole?

I'm certain that Scott and Amundsen didn't detect the exact South Pole but more less reached a position that explorers would think was close enough to count. One technique they probably used was to ...
M.A. Golding's user avatar
  • 1,288
5 votes

How did Eratosthenes know the distance between Aswan and Alexandria?

Based on the discussion of Eratosthenes' method in Daniel Špelda's Astronomie v Antice (Astronomy in Antiquity, ISBN 80-7225-210-0), the distance of 5000 stadia was estimated by Eratosthenes based on ...
Frigo's user avatar
  • 191
5 votes

Circular reasoning in Eratosthenes's measurement of the Earth's circumference

This might refer to the wrong circumference hypothesis, but it concerns not Eratosthenes but Ptolemy. There were many issues with Erathostenes's measurement, but circularity was not one of them, see ...
Conifold's user avatar
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5 votes

On Ptolemy climes

Originally, the Greek word κλῐ́μᾰ means “slope, incline, inclination,” and has nothing to do with the modern meaning of the word (long-term weather). Ptolemy defined the seven climata by the length of ...
Pierre Paquette's user avatar
5 votes

How many people knew that Earth is spherical in different ages?

In Medieval European and Muslim societies the educated believed in a spherical Earth, and there were very few geographical works which took biblical descriptins of a flat Earth seriously. However, it ...
M.A. Golding's user avatar
  • 1,288
4 votes

Why did Columbus think the Earth was much smaller than it is?

I think that observing ships disappear over the horizon would be an imprecise method of calculating the size of the Earth. [added 01-13-21 I found a quote where Aristotle (384-322 BC) mentioned that ...
M.A. Golding's user avatar
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4 votes

Did the coordinate system used by Eratosthenes influence the development of the Cartesian coordinate system?

Just an extended remark. There is nothing special about Eratosphenes here. Coordinates were used in astronomy since its very beginning, to describe stars positions. At least three of them were used ...
Alexandre Eremenko's user avatar
4 votes
Accepted

Did the coordinate system used by Eratosthenes influence the development of the Cartesian coordinate system?

It seems like it should have, but not really. Woodward in Medieval Mappaemundi tries to draw the connection thus: "In the words of a modern historian of mathematics: "The development of ...
Conifold's user avatar
  • 77k
3 votes
Accepted

Why does Eratosthenes method for calculating the circumference of the Earth requires the city of Alexandria and Syene to be in the same meridian?

The main reason is noon occurs at the same time on a meridian. The ancients didn't have accurate ways of keeping time, but everyone could tell when noon was because of the position of the Sun in the ...
Fred's user avatar
  • 348
2 votes

Why does Eratosthenes method for calculating the circumference of the Earth requires the city of Alexandria and Syene to be in the same meridian?

The reason mentioned in the answer of @zlaaemi is of course the most important one: the ancients could easily measure the difference in latitude, but not the difference in longitude. The "problem ...
Alexandre Eremenko's user avatar
1 vote

Why does Eratosthenes method for calculating the circumference of the Earth requires the city of Alexandria and Syene to be in the same meridian?

Below, B is X km north of A, while C is X km west of A. Since A and B are on the same meridian/longitude, the circle through them is a great circle, whose length is (approximately) the same as the ...
user103496's user avatar
1 vote

How did Eratosthenes know the distance between Aswan and Alexandria?

You might have heard of something called geometry. Geometry is from the Greek for "earth measurement", and ancient people use it for measuring land, or surveying. The ancient Egyptians ...
M.A. Golding's user avatar
  • 1,288

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