In Super Mario Galaxy, there are 7 Grand Stars. These special stars are earned by defeating major Bowser or Bowser Jr. bosses and power the Comet Observatory, Mario’s spacefaring hub.
The observatory contains six domes, which open access to the game’s galaxies as Mario collects stars. Five of the domes culminate in a boss stage that awards a Grand Star, accounting for five of the seven. The remaining Grand Stars come from the later Bowser encounters that lead toward the game’s climax.
Grand Stars are different from ordinary Power Stars, although both are central collectibles. Galaxy contains 120 standard stars for each playable character, plus an additional challenge star after completing the game’s requirements. The seven Grand Stars function primarily as progression keys rather than ordinary completion collectibles.
A common mix-up is confusing the number of Grand Stars with the total number of Power Stars. The game’s main star total is much larger, while Grand Stars are the rarer boss rewards that unlock new areas of the observatory.