In this video, author and presenter Lois Letchford reads from her book "Eureka" to introduce Claudius Ptolemy, an Alexandrian astronomer and geographer whose works shaped Western thought for over a millennium. She challenges the common claim that Ptolemy was the most important astronomer by arguing that his many errors are actually the starting point of scientific progress. Letchford outlines the scant biographical details known about Ptolemy—his active years (c. 90‑168 AD), his rooftop observatory in Alexandria, and his access to the great Library of Alexandria. She then shifts focus to Hipparchus, describing his groundbreaking contributions: accurate lunar distance, the first major star atlas, invention of celestial latitude and longitude, classification of stars by brightness, discovery of precession, and the formulation of a geocentric cosmology based on eight celestial spheres. The segment ends with a brief note that the dominant ancient view placed Earth at the universe’s center, contrasting with earlier heliocentric ideas, and a promise to return to Ptolemy in the next part.
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Hello, I'm Lois Letchford. I'm the author of the book Reversed: A Memoir and Literacy Problem Solver. Reading from the book Eureka, talking about the people who took us from fire, creating fire, to our world today. It's all built on foundations of people in the ancient world. And today I'm reading about Ptolemy. Claudius Ptolemy, who was— who lived about 90 AD to 168 AD, so after Christ. And this is Book of Cosmology, Ptolemy's Maps. An Alexandrian astronomer and geographer whose encyclopedic works guided Western thought for many Centuries. It would be easy to make the case that Ptolemy was the most significant astronomer the world has ever known. His ideas of how the universe worked dominated scientific thought, at least in the West, for something like 1,300 years. And then the book goes on to say, which is a pity because he got Just about everything wrong. I challenge that statement, and this is the way I read it. I challenge that statement because getting it wrong is a starting point. When you start, you don't always get everything right, and that's how science works. And you use the knowledge that you've got at the time to move forward, and you start to question, is this right, is this wrong? His knowledge started at 90 AD, 90 years after the birth of Christ. Except for the fact that Ptolemy lived and worked in Alexandria in Egypt, very few details of Ptolemy's life are known. His earliest astronomical observations, as recorded in his major astronomical treatise, dates from 127 And his latest 141 AD. Since he wrote other major books after that, it's reasonable to suppose he lived a couple of decades longer. Because of his name, some historians think he might have been born Ptolemaeus Hermene, a city on the west bank of the Nile, but they're really just guessing. In Alexandria, Ptolemy built himself a rooftop observatory so that far above the optical interferences of the city lights— meager by today's standards, of course— he could see the skies more clearly. More important, the city contained the greatest repository of knowledge in the ancient world. Its famous Library. Check out the Library of Ptolemy at Alexandrinia in Egypt. Among the works in which Ptolemy had access, there were writings of Hipparchus, arguably the greatest of Greek astronomers. Working in the 2nd century, Hipparchus made an accurate calculation of the moon's distance Constructed the first major star atlas, invented the concept of celestial latitude and longitude, and as a byproduct formalized the system of terrestrial latitude and longitude into something much like we use today. Saw the first recorded nova, although he had no way of knowing it was an exploding star. was the first to classify stars according to their brightness, discovered the famous precession of the equinoxes, and much more. Hipparchus also developed a cosmology that was hugely influential. Although Aristarchus of Samos and others correctly deduced that the Earth and planets went round the Sun, not the Sun went round the Earth, The major scientific view was that the Earth was the centre of the universe and everything circled it. Hipparchus subscribed to the Pythagorean notion of celestial spheres. In this scheme, there were 8 of them, the outmost being the stars, with the other 7 corresponding to known planets, plus the Moon and the Sun. So that's where I'm going to stop now because this is more on Hipparchus than Ptolemy, and I'll talk about Ptolemy next. Thank you. Hit like, hit subscribe, share, and enjoy the discovery of these people. Thank you.
