Questions tagged [ptolemy]

Ptolemy was an astronomer, mathematician, and geographer of Greek descent who flourished in Alexandria during the 2nd century CE.

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Did the Ptolemaic system have rotating center of the deferent for Venus?

I've come across this diagram of the Ptolemaic model. Am I understanding correctly that this means that all the planets' deferents rotate around a point which next to Earth, while Venus' deferent ...
Adrien Hingert's user avatar
1 vote
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How did the Astronomical model of Sacrobosco differ from Ptolemy's?

According to Wikipedia, Sacrobosco's De Sphaera described the Ptolemaic system, but drew on additional ideas from Islamic Astronomy. How did Sacrobosco's model differ from that of Ptolemy?
Michal Paszkiewicz's user avatar
19 votes
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How did Ptolemy know that days were unequal lengths?

Apparently Ptolemy was aware of the fact that the duration of time from noon to noon varied by many seconds throughout the course of a year. In modern times this fluctuation in length of day leads to ...
Jagerber48's user avatar
1 vote
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What was the Ptolemaic system used for?

Ptolemy's model is less accurate than Copernicus', but it is said to have been in use for a long time. What was the Ptolemaic model be used for?
BonBon's user avatar
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On the Ptolemaic theory of the planet's latitude

The Ptolemaic theory of the latitude of the planets is dealt on in Book 13 of the Almagest. This theory (which I was struggling to find info about online) is considered quite complicated, but luckily ...
d_e's user avatar
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The Rejection of Solid Orbs by Geo-Heliocentric (Tychonic) model of the solar system

Some sources (modern sources, and Kepler himself) claim that in his Geo-Heliocentric (Tychonic) model, Tycho Brahe saw that the orbs of the Sun and Mars intersect, and this was one of the reasons ...
d_e's user avatar
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Was Fourier inspired by Ptolemy?

Ptolemy invented a system to describe the periodic motion of the planets by epicycles. Fourier did something similar for periodic motion in mechanics. Every such motion can be thought of as ...
Deschele Schilder's user avatar
3 votes
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On Ptolemy climes

Reading Dante's Comedy, I was interested in understand a little bit how medieval geography worked, so I decided to have a look at Edward Luther Stevenson's translation of Ptolemy's Geographia. I've ...
Charo's user avatar
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Has anyone explored Ptolemy's epicycles as an early form of Fourier analysis?

Whilst researching science in the ancient world, I came across an observation, which unfortunately I did not make a note of, and so cannot credit, that Ptolemy's epicycles were an early form of ...
Mozibur Ullah's user avatar
5 votes
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Did Ptolemy and other Greek scientists actually measure the distance to the Sun?

According to Subhash C. Kak: Early Theories on the Distance to the Sun: “Pancavimsa Brahmana states that the heavens are 1000 earth diameters, de, away from the earth. The sun was also taken to be ...
Mikael Jensen's user avatar
6 votes
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Where did Ptolemy compare the Earth to the distance of fixed stars?

I read the following in C. S. Lewis, Miracles (page 77-8) The immensity of the universe is not a recent discovery. More than seventeen hundred years ago Ptolemy taught that in relation to the ...
Frank Hubeny's user avatar
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How did Ptolemy calculate the distance to the Moon?

I've read somewhere that Hipparchus measured the distance to the Moon using the lunar and solar eclipse and obtained a value of around 67.3 Earth radii. It also says that soon after Ptolemy gave a ...
cal's user avatar
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What is Ptolemy holding in this picture?

I would like to know the name of the device Ptolemy is holding in the following picture. [Image Source]
hb20007's user avatar
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