Thales of Miletus

The great ancient Greek philosopher Thales, often known for his famous theorem , Thales’ theorem, which we all end up learning in high school. But do we really know who Thales is?

Thales was born in Miletus (ancient Greek city, currently in Turkey)  around the year -625 BC. He  is considered one of the seven sages of ancient Greece. The young mathematician learned science in Egypt thanks to the knowledge of the Egyptian and Babylonian priests.

Later, he learned geometry, astronomy, and philosophy . The Egyptian pyramids were often the subject of scientific experiments for the young apprentice.

After a few years, Thales returned home to Miletus to found the Milesian school. The great mathematician became a teacher and taught all his discoveries to his disciples while continuing his research in different fields.

To find the theorem that we know today, Thales is said to have wanted to calculate the height of a pyramid through the shadow of a stick .

This is how Thales invented this famous theorem :

«Let’s draw a triangle ABC and two points D and E of lines (AB) and (AC) so that line (DE) is parallel to line (BC), in such a way that we can say that: AD / AB = AE / AC = DE / BC ‘.

Thales also used his knowledge in the field of astronomy and discovered how to use Ursa Minor to guide sailors in the open sea, calculate the length of the year through the intervals of the solstices at the equinoxes, indicate the distance traveled by the sun between the two tropics, the repertoire of ephemeris, etc.

Thales died around the year -547 in Miletus .

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