In Super Mario Galaxy, what is the name of Rosalina's spaceship?

In Super Mario Galaxy, Rosalina’s spaceship is the Comet Observatory.

The Comet Observatory is both Rosalina’s home and the central hub of Mario’s journey through space. It normally travels across the cosmos, but Bowser steals its Power Stars, leaving it unable to move. Mario collects those stars from different galaxies and gradually restores the Observatory’s power.

The Observatory is divided into several domes, each acting as a gateway to groups of galaxies. Its observatory-like design reflects its role as a cosmic navigation center, while the Lumas live aboard it with Rosalina. As Mario gathers enough Power Stars, the ship eventually travels to the center of the universe for the final confrontation with Bowser.

A common mix-up is confusing the Comet Observatory with Starship Mario, which is the mobile spaceship used in Super Mario Galaxy 2. Peach’s Castle is transported into space during the opening story, but it is not Rosalina’s vessel.