Beacon

"That ball of flame represents the power of the observatory. We call it the beacon. When you recover a Grand Star, a little Star Power will be restored, and the beacon will grow."

- Rosalina

The Beacon is a large star-like reactor that powers the Comet Observatory, including the space station's propulsion systems, life support, and its Domes. The Beacon begins as a small, dim star, but as Mario collects more Grand Stars, the star becomes larger and brighter, allowing access to more Domes. The Lumas need the beacon to survive. Through the course of the game, it changes colors from burgundy (No Grand Stars) to orange (1 Grand Star), then yellow (2 Grand Stars), green (3 Grand Stars), greenish-blue (4 Grand Stars), blue (5 Grand Stars), and finally turquoise (6 Grand Stars). There is also an invisible wall that prevents the player from touching the Beacon.

In Super Mario Galaxy 2, Starship Mario has, in its engine room, what appears to be a miniature beacon that runs on Power Stars. This miniature beacon is the energy source for the starship. It is additionally only colored turquoise for the entire game.

Trivia

 * It is notable that as Grand Stars are fed to the Beacon, it grows and starts glowing further up the colour spectrum. This may perhaps be a nod to the fact that the larger a star, the hotter it burns. Brown and red are generally reserved for the smallest but longest-lived of stars, while blue is generally reserved for massive stars that quickly burn out and die in a supernova.