When We Discovered Pluto, It Changed How We Saw The Solar System

On the 23rd and 24th of January, 1930, a young astronomer working in Flagstaff, Arizona, scanned a small patch of the night sky. He was taking pictures of star positions, looking for anomalies that would signal movement somewhere at the edge of the solar system. He took the pictures then set them aside, not realizing that he'd found exactly what he was looking for: a ninth planet in the solar system.