On August 24, 2006, a group of astronomers made a big announcement: Pluto could no longer be considered a planet. This book explains how advancements in technology have changed our understanding of the universe--and exactly how and why the number of planets in our solar system went from nine to eight.

Introduction --The wanderers -- Some early astronomers -- Ideas that work--and those that don't -- Pluto's problems -- Finding planets -- What is a planet?