When did it become clear that the earth was round?

The realization that the Earth is spherical emerged through various observations and measurements over centuries. Here's a structured overview:

Ancient Observations

• Aristotle's Observations (4th Century BC): Aristotle noted that during lunar eclipses, Earth's shadow on the Moon was round, suggesting a spherical Earth. He also observed that travelers moving southward saw southern constellations rise higher above the horizon, indicating Earth's curvature.

Scientific Measurements

• Eratosthenes' Calculation (3rd Century BC): Eratosthenes accurately estimated Earth's circumference by measuring the angle of the Sun's rays at two different locations in Egypt. His method involved comparing the shadow lengths at Alexandria and Syene at noon during the summer solstice.

Empirical Evidence

• Magellan-Elcano Circumnavigation (1519–1522): The expedition led by Ferdinand Magellan and completed by Juan Sebastián Elcano provided practical evidence of Earth's sphericity by successfully circumnavigating the globe.

Modern Confirmation

• Space Exploration (20th Century): Photographs of Earth taken from space provided clear visual evidence of its spherical shape. For instance, the Apollo missions in the 1960s and 1970s captured iconic images of Earth from the Moon.

Through a combination of philosophical reasoning, scientific measurement, exploration, and modern technology, humanity has come to understand and confirm that the Earth is round.