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The armillary sphere or spherical astrolabe is an astronomical instrument that first appears in the third century B.C. Probably designed by Eratosthenes, director of the Alexandria Library. But it is associated more with Ptolemy, who was the one who perfected it in the s. II.
The armillary sphere represents the geocentric model of the Cosmos. Ancient Greek and Babylonian civilizations believed that the Earth was the center of the Universe. The sun, the moon, the planets and the stars revolved around it. Aristotle, Plato and the Christian tradition also adopted this vision. Man was the center of Creation.
In an armillary sphere the Earth appears in the center. Through a complex system of turns, Ptolemy managed to explain the apparent recoil in the movement of the planets. The Ptolemy sphere was so precise that even today it can be used to orient itself in maritime navigation. Although we know that your system is wrong, if we take our position as fixed, the position of the stars indicated by the astrolabe coincides with what we can see in the sky.
Ptolemy's universe model is what inspired Dante Alighieri to write the Divine Comedy.
This was the vision of the world until the arrival of Copernicus in the 16th century. Although the geocentric model is overcome today, our language still remembers that old thought: we still say the Sun rises, the Sun sets ...
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