The astronomer, mathematician, and physician Eudoxus of Cnidus (ca. 408-ca. 355 BC) was the first Greek astronomer to properly apply mathematics to astronomy.

Eudoxus was born in Cnidus, a Greek colony in Asia Minor, into a family of physicians; he studied at the medical school there. At the age of 23 he went to Athens as an assistant to a doctor. He attended lectures at the Academy, recently founded by Plato. On returning to Cnidus, Eudoxus completed his studies.

A few years later Eudoxus went to Egypt with another doctor. He studied the heavens from an observatory at Heliopolis on the Nile. His astronomical observations appear in his Phaenomena, but apparently this book did not contain theories such as those he was later to expound. The book locates the constellations relative to each other and to imaginary lines on the celestial sphere. Much space is given to a compilation of...