2900 B.C.

2900 B.C. Three independent lines of reasoning all lead to the date of 2900 BC for the origin of the constellations: 1) that was the time when the part of the sky they occupy was all visible, 2) that was when their boundaries would have been parallel or perpendicular to the celestial equator, and 3) that was when their times of rising and setting corresponded to tradition. See Pratt, J.P. Dating the Constellations Cited from Pratt, The Constellations