The man who gave Euclid’s Elements a final chapter and the zodiac some math. Hypsicles of Alexandria (fl. 2nd century BCE) added Book XIV to the Elements and wrote a treatise on the rising times of zodiac signs — blending geometry and astronomy in smooth, ancient fashion. He stood at the crossroads of number theory and star lore, making the heavens just a little more countable. Quietly brilliant, Hypsicles brought a mathematician’s eye to celestial rhythms.