I've heard this song's story before.
The story in the song is the same as the story you unlock piece by piece in Super Mario Galaxy in Rosalina's Library she reads this story to the Star Children (The Lumas) and it is actually the story of her roots and the origin of the Comet Observatory.
Don't believe me? While Fredde Gredde may not have noticed it this is the same story. Just look it up.