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A student of ancient Greek philosopher Plato presented the first mathematical theory of the universe about a hundred years later. -
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The ancient Greek mathematician Pythagoras suggested that the Earth is spherical in about 500 BCE, and this was accepted by most ancient Greek philosophers at the time. -
The ancient Greek philosopher Aristotle extended Eudoxus’ model of the universe in the 4th century BCE. Aristotle’s model of the universe was also geocentric, with the Sun, Moon, planets, and stars all orbiting the Earth inside of Eudoxus’ spheres. Aristotle believed the universe is finite in space but exists eternally in time. -
Aristarchus attempted to calculate the relative distance between the Earth and the Sun in the 3rd century BCE. He did this by measuring the angle between the Moon and the Sun during a half moon and using trigonometry. -
Ptolemy developed Aristotle’s geocentric theory of the universe in about 150 CE. Ptolemy knew that the planets don’t appear to orbit in perfect circles around the Earth. -
The Polish astronomer Nicolaus Copernicus reintroduced the idea of a heliocentric universe in On the Revolutions of the Celestial Spheres, first published in 1543. Like Ptolemy, Copernicus believed that the planets only travel in perfect circles, and so his heliocentric model needed a similar amount of epicycles to explain their observed motions.