> The phenomenon of precession — in which Earth slowly wobbles on its axis by around one degree every 72 years — means that the position of the fixed stars slowly shifts in the sky. The researchers were able to use this to check when the ancient astronomer must have made his observations, and found that the coordinates fit roughly 129 bc — during the time when Hipparchus was working.

That's amazing, using the discovered results themselves to step backwards and find out when the observations were made.