Comet Observatory

"Welcome to the Comet Observatory. It's my home, and also home to the Lumas."

- Rosalina

The Comet Observatory is one of the many areas from Super Mario Galaxy for the Wii. It acts as the hub area, similar to Peach's Castle in Super Mario 64 and Super Mario 64 DS or Delfino Plaza in Super Mario Sunshine. The Comet Observatory is controlled by Rosalina, and acts as the home of both her and the Lumas.

Super Mario Galaxy
It was built by Rosalina and Luma after Rosalina agreed to take care of him. Over time, it grew to be much too big for just the two of them. Soon, other Lumas came to live in the Comet Observatory as well, and Luma transformed into the Beacon that powers the Observatory.

The Comet Observatory normally comes into orbit around the Mushroom World every 100 years, and during that time, the people of the Mushroom Kingdom celebrate the Star Festival, thinking that the observatory is simply a comet. During the most recent Star Festival however, Bowser's forces attacked the Comet Observatory, causing it to lose its power source: Grand Stars and Power Stars. They were scattered throughout the cosmos following the attack, causing the Comet Observatory to remain immobilized above the Mushroom Kingdom. He later attacked Toad Town during their celebrations. Only after Mario recovers five out of seven Grand Stars can the Observatory fly like a starship again. When this has been accomplished, Rosalina takes Mario (or Luigi) to the Center of the Universe to rescue Princess Peach.

The Comet Observatory can be accessed through a portal in the Gateway Galaxy. Much like Peach's Castle in Super Mario 64 or Delfino Plaza in Super Mario Sunshine, certain parts of the observatory are unlocked as Mario gradually acquires Grand Stars and Power Stars. This is because the Grand Stars are used to power the large Beacon in the middle of the Comet Observatory, which enables it to transform into a comet and fly across the cosmos. Once five Grand Stars have been acquired, the observatory will have enough power to travel toward the center of the universe. After six Grand Stars have been obtained while the total Stars obtained is less than 60, Polari says that the beacon is the brightest that it can be.

There are six domes located throughout the Comet Observatory, which act as Mario's means of accessing all of the galaxies that he will encounter in the game. In order, the domes are the Terrace, the Fountain, the Kitchen, the Bedroom, the Engine Room, and the Garden. Galaxies are accessed by collecting multiple Power Stars to unlock more and more domes. Additional Galaxies can be unlocked by feeding the seven Hungry Lumas that appear outside each dome (and the Gate). According to the Lumas, the domes are used to view the cosmos. Other areas in the Observatory are the Garage, the Library, and the Gate.

After Bowser's giant sun collapses into a massive Black Hole following his defeat by Mario in the final battle, the Comet Observatory is pulled toward the Black Hole. Parts of the observatory were broken off and scattered as Peach's Castle crashed into the side of it. However, the Lumas all sacrificed themselves by jumping into the black hole, creating a large explosion and reforming the entire cosmos. It can also be inferred that this explosion reformed the Comet Observatory, as it is seen intact in the ending sequence after collecting 120 Power Stars and defeating Bowser a second time. Rosalina transforms it into a comet once again and then flies off to parts unknown.

Super Mario Galaxy 2
The Comet Observatory makes an appearance in Super Mario Galaxy 2. After Mario has beaten Bowser for the final time. When Mario returns to Starship Mario with Peach and the Grand Star, Rosalina appears piloting the Comet Observatory in its comet form, which quickly transforms back to its regular form. As soon as it does this, the Comet Observatory theme begins to play in the background, until Rosalina is reunited with the baby Luma, after which they fly off in the Comet Observatory once again.

Mario Kart 7
The Comet Observatory appears on the side of the Rosalina's Ice World course, it serves only as a background of the course.

Mario Tennis Open
The Comet Observatory appears in an unlockable stage, Galaxy Arena.

Trivia

 * Part of the Comet Observatory theme plays in the Grandmaster Galaxy mission "The Perfect Run", along with the Gusty Garden Galaxy theme, the Good Egg Galaxy theme, and the Bowser's Galaxy Reactor theme. Also, the final planet of the Prankster Comet mission in this galaxy is almost an exact replica of the Gate.
 * It's impossible for the player to lose a life on the Comet Observatory, as jumping or falling off the side of it causes Mario or Luigi to be enveloped in an energy-like bubble and return to safe ground.
 * After completing Bowser's Galaxy Reactor for the first time, a countdown will appear on the tiles underneath Rosalina (talking to her again from that point on will result in her asking if the player want to complete that level again) determining how many Power Stars are still left to be collected. When all of the stars are finally collected, fulfilling 100% completion, then the countdown will read zero.
 * The Comet Observatory was actually created very late in the game's development, originally the Starship Mario was going to be the hub level, but wasn't used until the sequel.