The Grand Star are six very large Stars in Super Mario Galaxy. As Mario gets these Grand Stars, he gains access to different parts of Princess Rosetta's observatory. Princess Rosetta provides Mario with a young Luma named Tyke who is going to assist him in his quest to save his first Grand Star. Mario then sets out through the Gateway Galaxy, eventually finding a Grand Star inside a planet. A Luma tells him that the Bad Guys are using the Grand Stars to power Something. Mario must then complete a simple puzzle to free it. Mario receives another Grand Star after defeating Megaleg. Two more are found after defeating Bowser and Bowser Jr.. When one is found a path to a new observatory is created. There are 6 Grand Stars in the game. When all 6 are found you will able to fly to the Center of the Universe to confront Bowser for the final battle. The grand stars have the same goal as the Key's from Super Mario 64.
File:Grandsuperstar.jpg
Mario getting a Grand Star.