Whatsoever is discovered by men of a later day must none the less be referred to the ancients, because it was the work of a great mind to dispel for the first time the darkness the discovery who hoped that the discovery could be made.

• What happened to the knowledge of the ancient astronomers after the fall of the Roman Empire?
• How is it possible for the heliocentric model of Copernicus to account for the diurnal motion of the celestial objects, the annual motion of the Sun, and the complicated motions of the planets?
• What does the heliocentric model have to say about the orbital distances and periods of the planets?
• Why did Tycho Brahe, the great observational astronomer, reject the heliocentric model of the solar system?
• How were Tycho’s observations used by Kepler to produce his laws of planetary motion?
• What are the shapes of planetary orbits? How does the speed of a planet’s revolution depend on its distance from the Sun?
• How did the telescopic observations of Galileo support the heliocentric model of the solar system?
• What finally convinced the world that the Earth revolves around the Sun rather than the other way around?