Question

Read the following excerpt from Ball's chapter on Ptolemy in Great Astronomers.

Answer 1

According to Ptolemy’s theory, Earth was at the center of the solar system. To a modern-day reader, this theory will make no sense because it’s well established that the sun is the center of the solar system. This diagram helps the reader picture what Ptolemy’s theory is all about.

The text describes the movement of the sun and the planets around Earth based on Ptolemy’s theory. The diagram aids in the reader’s understanding of the text; it clearly shows the ideas Ptolemy proposed. Earth is shown at the center, and the sun and the planet Venus are shown circling around Earth. Venus is also shown making a circular motion around a point on its path around Earth. Using this diagram, Ptolemy explained the movement of Venus across Earth’s sky from morning to evening and the reason Venus sometimes appears on one side of the sun and sometimes on the other.