Determining the earth's shape

Today, when you ask anyone to describe the shape of the earth, they immediately tell you it is round. Of course, they mean that it's round like a ball, not round like a circle or a disk. To be more precise, we would say its shape is spherical. While today a discussion about the earth's shape may be a matter of semantics, historically, the shape of the earth has not enjoyed such a wide consensus.

In 3000 BCE (Before Common Era), the Babylonians believed the earth to be shaped like an oyster. Much later, two Greeks, the philosopher Thales (600 BCE) and the poet Homer (800 BCE), thought the earth was a flat disk. As time passed, various other shapes were proposed, such as a cylinder and a cube. As late as the sixteenth century, the earth was described by Christopher Columbus as a roundish pear.

By 500 BCE, the Greek mathematician and philosopher Pythagoras declared the earth's shape to be a sphere. He arrived at this determination not through scientific observations but because he believed the sphere to be the perfect geometric shape and the gods would only create a "perfect" world.

The ancient Greeks liked geometric shapes and the mathematical harmony of nature. This preference probably influenced their speculations about the shape of the earth.

Supported by scientific observations, such as that of the silhouette of the earth on the moon during a lunar eclipse, Pythagoras' assumption eventually proved correct.

By the European Middle Ages, most scholars accepted the sphere as the earth's true shape, but many non-scientists still believed the earth was flat. With the coming of the Renaissance and the rediscovery of ancient Greek texts, the flat earth theory reluctantly gave way to that of the sphere

Using a circle's diameter as an axis and rotating the circle 360 degrees creates a perfect sphere.