This is the first book in the series. Asimov chose a good subject to begin with. This book takes us from myths to the first moon landings, when after 1000s of years of careful reasoning it was possible to confirm the conclusion by just looking.

Chapter 1: Is the Earth Flat?
Lots of illustrations of various myths. Anaximander observes the movement of the stars and decides that the earth is a disk surrounded by a sphere which spins around the north pole.

Chapter 2: The Disappearing Stars
As one travels north or south, the set of stars that are visible at night changes. From this Anaximander concluded that the earth possessed a curvature, and imagined that it might be a cylinder. At the same time, observations of the moon and its phases indicate that it is most likely a sphere. Question: Since we only see one side of the moon, can be prove that it is a sphere geometrically? Or are there other possibilities?

Chapter 3: The Disappearing Ships
Ships sail out of sight hull first, regardless of their direction. This is good evidence that the earth is actually a very big sphere, i.e, its curvature is not just north-south, but also east-west. Of course, again, those observations could have been just local. Or maybe the oceans bulged upward?

Chapter 4: The Earth's Shadow
During a lunar eclipse, the shadow of the earth that can be observed on the moon is always a segment of a circle. This is strong evidence for a spherical earth. Philolaus (circa. 450 BC), was the first to make the spherical earth assertion.

Chapter 5: The Size of the Earth
Eratosthenes works out the circumference of the earth using basic geometry/trigonometry. But others disagree, and prefer a smaller estimate. Ptolemy supports the smaller estimate and this is the value Columbus uses when he sails across the Atlantic. Columbus believes in it until he dies but others put forward a different view. Finally, everybody acknowedges that a new continent has been found. Magellan's crew sails around the world which is a clincher. And astronauts hit the moon, and take some very convincing photos.

THE END ( )