Summary
Highlights
Born during the golden age of classical Greece, Aristotle was a pupil of Plato, tutor to Alexander the Great, and eventually opened his own school. His contributions encompassed physics, metaphysics, philosophy, biology, astrology, and psychology, and he played a key role in developing the scientific method. His most significant achievement, however, was proving that the Earth is a sphere with the help of the moon.
Aristotle used four main arguments to conclude the Earth was a sphere. First, all earthly substances move towards the center, converging into a sphere. Second, the change in visible stars when traveling north or south indicates a curved surface. Third, as ships sail away, their top masts disappear last, proving the Earth's roundness. Fourth, the Earth's shadow on the moon during a lunar eclipse is always circular.
Aristotle reached his conclusion primarily through observing lunar eclipses. He noticed that the Earth's shadow projected onto the moon was always curved. By likening the shadow to a reflection, he inferred that if the outline of the Earth was round, the Earth itself must also be round.
Addressing the possibility of a disc-shaped Earth, Aristotle reasoned that if the Earth were a disc, its shadow would appear eccentric and oblong depending on its orientation. However, he observed that the Earth's shadow always remained circular, regardless of position. A sphere is the only shape whose shadow appears circular from every angle, solidifying his conclusion that the Earth is spherical.
Based on his observations, Aristotle predicted that in every future lunar eclipse, the Earth's shadow would be round, irrespective of the planet's orientation or the viewer's location. This prediction has held true to this day, confirming his remarkable insight.