World 1 (Super Mario Galaxy 2)
From the Super Mario Wiki
World 1: The Great Space Journey Begins is the first world featured in Super Mario Galaxy 2. It is a sky area filled with big white clouds. The Mushroom World (which can be seen from the map) is located in this world. It holds seven galaxies, the last of which, Bowser Jr.'s Fiery Flotilla, features the first encounter with Bowser Jr., who sends Gobblegut to attack Mario.
The music that plays on the World 1 map is initially the same as the music for World 2. However, after Mario has collected at least 120 Power Stars, the music becomes a quiet, slowed-down rendition of the theme from the Good Egg Galaxy.
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