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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
  • 1,323
11 votes
Accepted

Could ancient astronomers have proven heliocentrism?

You can't ever "prove" heliocentrism! (We can't even today. Thinking that science "proves" things is not at all helpful in doing science.) What we can do is show that a ...
Mark Olson's user avatar
5 votes

How did Ptolemy calculate the distance to the Moon?

Ptolemy knew about the Moon's parallax (he explains it in section 11, Ch. V of Mathematical Syntaxis). To measure it he invented the "parallactic instrument" described in section 12. Section 13 is ...
Alexandre Eremenko's user avatar
5 votes
Accepted

Greek astronomy vs astrology

There was a link between astronomy and astrology, as @Mauro Allegranza notes but the two things were strictly separated. Ptolemy's Almagest (and his many other scientific books) contains no single ...
Alexandre Eremenko's user avatar
5 votes

How did Khayyam calculate the year so accurately?

Khayyam simply did not achieve this precision. It is an urban myth, typically lacking any proper sources and references. Only occasionaly one finds mentions such as "the Persian calendar using ...
sand1's user avatar
  • 2,422
4 votes
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How did Hipparchus measure the length of the tropical year?

A hindrance to answering this question is that we do not have any description from Hipparchus himself on how he derived his numerical results, whether for the length of the year or of the seasons. His ...
terry-s's user avatar
  • 4,600
4 votes
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Did the Ptolemaic system have rotating center of the deferent for Venus?

There were multiple versions of the Ptolemaic system circulating in the middle ages, including those where Venus did have a rotating eccentric, the center of the deferent, e.g. in Regiomontanus's ...
Conifold's user avatar
  • 77.6k
3 votes
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How did the ancients determine the exact time of equinoxes and solstices?

As Ptolemy describes, for equinoxes, he had a flat bronze ring installed parallel to the equator. When the Sun is one one side of the equator, the corresponding side of the ring is illuminated. The ...
Alexandre Eremenko's user avatar
3 votes
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Earth's and Sun's rotation in the Ptolemaic world

In Ptolemy system, there is a sphere of fixed stars which rotates about the Earth with constant speed 1 rotation per 24 hours. This rotation is about the axis which passes through the North and South ...
Alexandre Eremenko's user avatar
3 votes

When and how was it discovered that the sun was in different positions depending upon longitude?

This is an immediate logical consequence of sphericity of the Earth. Greek tradition credits sphericity to Pythagoras, but modern historians even doubt that he ever existed. So the question has no ...
Alexandre Eremenko's user avatar
3 votes
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What role did meteors and comets play in early astronomy?

None. Ancient Greeks subdivided the world into and the superlunar the sublunar spheres, the heavens and the Earth. The former a place of perfection and order, the latter, not so much. Since meteors ...
Conifold's user avatar
  • 77.6k
2 votes

Did knowledge of astronomy spread among Indo-European civilizations in antiquity?

Much of the ancient transmission went through Greece. Astronomical (and other) knowledge was transmitted from Egypt to Greece at least by the time of early Pythagoreans (c. 500 BC), likely earlier. ...
Conifold's user avatar
  • 77.6k
2 votes

How did ancients differenciate between inner and outer planets?

A useful source on this subject is Olaf Pedersen's Early Physics and Astronomy: A Historical Introduction, (first published 1974, CUP reprint 1993). Much is shrouded in the mists of pre-history, but ...
terry-s's user avatar
  • 4,600
2 votes

What is the historical basis for the length of a sidereal year?

By looking at stars position with respect to the point of intersection of the ecliptic and equator (this is a position of the Sun at the equinox). Or which is the same at the position of this point ...
Alexandre Eremenko's user avatar
2 votes

Did the Mayan's really predict the solar eclipse?

Yes, they really predicted the 1991 solar eclipse. I suggest that you read Classic Maya Prediction of Solar Eclipses, by Harvey M. Bricker and Victoria R. Bricker, together with comments and replies (...
José Carlos Santos's user avatar
2 votes
Accepted

Length of the year in Aztec/Maya calendar

The standard literature on the Mayan calendar is: J. Eric S. Thompson, Maya Hieroglyphic Writing, Washington : Carnegie Institution, 1950. Lis Brack-Bernsen, 'Die Basler Mayatafeln', Verhandlungen ...
fdb's user avatar
  • 3,485
2 votes

How did the ancients determine the exact time of equinoxes and solstices?

Ancient astronomers could find the dates of solstices and equinoxes for many years in a row (except for years they were not observable, and add up the total days between events separated by many years ...
M.A. Golding's user avatar
  • 1,323
2 votes

Ancient parallax

They tried to find parallax between pairs of stars. First of all, they didn't "believe" that stars were on the same distance. That was their hypothesis. And one of the reason why they ...
Alexei Kopylov's user avatar
1 vote

The Sun's direction of rotation in the geocentric model

Sun (and everything else in the sky) participate in two motions. Sky as a whole (the sphere of fixed stars) rotates clockwise, 1 rotation per 24 hours. BTW for this reason we call this direction ...
Alexandre Eremenko's user avatar
1 vote

Is it possible to narrow down possible dates for the following eclipse pattern?

Since you write that your main problem is conversion of the dates from Gregorian to Julian calendar, let me give reference for algorithms. Jean Meus, Astronomical algorithms, William-Bell Inc., ...
Alexandre Eremenko's user avatar
1 vote

Spirals as calendrical representations

New is well forgotten old, it seems. In a couple of papers from 1916 Marcel Baudouin discusses as matter of fact the linking of spiral and the Sun's path: The spiral represents the Sun's path in ...
sand1's user avatar
  • 2,422
1 vote

How did ancients differenciate between inner and outer planets?

Of course everything orbits around the earth. Lumenlearning Some planets (the inner planets) sometimes pass between the sun and the earth, meaning their orbints are inside the orbit of the sun. ...
Gerald Edgar's user avatar
  • 10.4k
1 vote

How did ancients differenciate between inner and outer planets?

This is an immediate conclusion from direct observation of the sky. Mercury and Venus accompany the Sun: are never far away from the Sun. Outer planets behave very differently: they can be at any ...
Alexandre Eremenko's user avatar
1 vote

When and why did the 'spiky star' appear as an image in art and science?

Here are some Roman Denari. Moon and stars. Looks like points on the stars.
Gerald Edgar's user avatar
  • 10.4k
1 vote

Length of the year in Aztec/Maya calendar

FWIW: ~ Gama, 1790, P.25 indicates "...pero la corrección no se hacia hasta el fin del Ciclo, en que se intercalaban juntos los 13 días, que gastaban en fiestas, en honor de los dioses seculares, ...
dxxds's user avatar
  • 11
1 vote

Why did the ancients believe celestial matter was of a different type than terrestrial matter?

The underlying issue, in today's language, was that he needed two different models to explain observations on Earth and in the sky. For instance in his model about earthly matter he wrote that a ...
Rad80's user avatar
  • 111
1 vote

Why did the ancients believe celestial matter was of a different type than terrestrial matter?

The question is rather misleading. The different clestial matter was a successful theory devised by Aristotle. The sources being what they are, it is rather speculative to tell what the ancients ...
sand1's user avatar
  • 2,422

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