Summary of Stephen Hawking's A Brief History of Time

Please note: This is a companion version & not the original book. Book Preview: #1 The ancient Greek philosopher Aristotle believed that the earth was a round sphere rather than a flat plate. He knew that eclipses of the moon were caused by the earth coming between the sun and the moon, and that the North Star appeared lower in the sky when viewed in the south than it did in more northerly regions. #2 Aristotle believed the earth was the center of the universe, and that circular motion was the most perfect. This idea was elaborated by Ptolemy in the second century AD into a complete cosmological model. #3 The Ptolemaic model was a reasonably accurate system for predicting the positions of heavenly bodies in the sky. However, it made an assumption that the moon followed a path that sometimes brought it twice as close to the earth as at other times. #4 The Copernican model got rid of Ptolemy’s celestial spheres, and with them, the idea that the universe had a natural boundary. Since fixed stars did not appear to change their positions apart from a rotation across the sky caused by the earth spinning on its axis, it became natural to suppose that the fixed stars were objects like our sun but much farther away.