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Ptolemy's universe


about the nature of the cosmos

It is not surprising that we thought the Earth was flat at the beginning. It really seems that way to one who has never travelled far from his or her home village. Both the Sun and Moon appear to circle around us, and the stars must certainly be holes in the arching bowl of the night sky, allowing us but a glimpse of the heavenly light outside.

Obviously somewhere there must be a limit to this world. Not advisable to try and find it. One might fall over the edge.


After centuries of observation, it was realized that the Earth could not possibly be flat, that in actual fact it must be a sphere.

The question remained: how to explain why some of the glowing pricks of light in the night sky were fixed, and some moving, often in irregular and very puzzling ways?

A solution was proposed by the Alexandrian Claudius Ptolemy in his Book Almagest, published in about 150 AD. In Ptolemy's model, the Earth is the immoveable centre of the cosmos. The Sun and planets are attached to crystal spheres that rotate at different speeds around the Earth. Beyond the outermost sphere lies God's heaven with its choirs of angels. The yellow band in the illustration on the left shows where the solar sphere lay in this Earth-centered scheme of things.


Crystal spheres