Eudoxus of Cnidus
Previously, Eudoxus of Cnidus in the 4th century BC had described the stars and constellations in two books called "Phaenomena" and "Entropon". Aratus wrote a poem called "Phaenomena" or "Arateia" based on Eudoxus's work. Hipparchus wrote a commentary on the "Arateia" – his only preserved work – which contains many stellar positions and times for rising, culmination, and setting of the constellations, and these are likely to have been based on his own measurements.