Galaxy

A galaxy is an enormous system consisting of gases, stars, planets, and comets. Mario visits many galaxies in his adventures through Super Mario Galaxy and Super Mario Galaxy 2. There are currently a total of 91 different galaxies between the two games.

Super Mario Galaxy series
The galaxy named Grand Finale Galaxy is home to Mario's planet (Mushroom World), while the Milky Way Galaxy is home to Earth. The galaxies in Super Mario Galaxy are notably much smaller than real galaxies, often being comprised of nothing more than a few small planetoids, most of which are in all different shapes and sizes. However, if one considers that the Mushroom Universe to be a different Universe to Earth, the laws of physics may be different to ours in where a Planet does not have to be spherical or a galaxy can be much smaller than a galaxy in our universe.

Galaxies are each categorized under different Domes which show Mario up to five galaxies and then gives him the option to fly to those galaxies. Each dome also has one Hungry Luma galaxy which can only be accessed by feeding a Hungry Luma the certain amount of star bits that it requires to transform into a galaxy.

Many galaxies have black holes, in which if Mario falls over the edge, he will be sucked into the black hole.

Gate

 * Gateway Galaxy
 * Boo's Boneyard Galaxy (Hungry Luma)

Terrace

 * Good Egg Galaxy
 * Honeyhive Galaxy
 * Loopdeeloop Galaxy
 * Flipswitch Galaxy
 * Bowser Jr.'s Robot Reactor
 * Sweet Sweet Galaxy (Hungry Luma)

Fountain

 * Space Junk Galaxy
 * Rolling Green Galaxy
 * Battlerock Galaxy
 * Hurry-Scurry Galaxy
 * Bowser's Star Reactor
 * Sling Pod Galaxy (Hungry Luma)

Kitchen

 * Beach Bowl Galaxy
 * Bubble Breeze Galaxy
 * Ghostly Galaxy
 * Buoy Base Galaxy
 * Bowser Jr.'s Airship Armada
 * Drip Drop Galaxy (Hungry Luma)

Bedroom

 * Gusty Garden Galaxy
 * Freezeflame Galaxy
 * Dusty Dune Galaxy
 * Honeyclimb Galaxy
 * Bowser's Dark Matter Plant
 * Bigmouth Galaxy (Hungry Luma)

Engine Room

 * Gold Leaf Galaxy
 * Sea Slide Galaxy
 * Toy Time Galaxy
 * Bonefin Galaxy
 * Bowser Jr.'s Lava Reactor
 * Sand Spiral Galaxy (Hungry Luma)

Garden

 * Deep Dark Galaxy
 * Dreadnought Galaxy
 * Matter Splatter Galaxy
 * Melty Molten Galaxy
 * Snow Cap Galaxy (Hungry Luma)

Trial Galaxies

 * Bubble Blast Galaxy
 * Rolling Gizmo Galaxy
 * Loopdeeswoop Galaxy

Other

 * Bowser's Galaxy Reactor
 * Grand Finale Galaxy

World 1

 * Sky Station Galaxy
 * Yoshi Star Galaxy
 * Spin-Dig Galaxy
 * Fluffy Bluff Galaxy
 * Flip-Swap Galaxy (Hungry Luma)
 * Rightside Down Galaxy
 * Bowser Jr.'s Fiery Flotilla

World 2

 * Puzzle Plank Galaxy
 * Hightail Falls Galaxy
 * Boulder Bowl Galaxy
 * Cosmic Cove Galaxy
 * Wild Glide Galaxy
 * Honeybloom Galaxy (Hungry Luma)
 * Bowser's Lava Lair

World 3

 * Tall Trunk Galaxy
 * Cloudy Court Galaxy
 * Haunty Halls Galaxy
 * Freezy Flake Galaxy
 * Rolling Masterpiece Galaxy
 * Beat Block Galaxy (Hungry Luma)
 * Bowser Jr.'s Fearsome Fleet

World 4

 * Supermassive Galaxy
 * Flipsville Galaxy
 * Starshine Beach Galaxy
 * Chompworks Galaxy
 * Sweet Mystery Galaxy (Hungry Luma)
 * Honeyhop Galaxy
 * Bowser's Gravity Gauntlet

World 5

 * Space Storm Galaxy
 * Slipsand Galaxy
 * Shiverburn Galaxy
 * Boo Moon Galaxy
 * Upside Dizzy Galaxy
 * Fleet Glide Galaxy (Hungry Luma)
 * Bowser Jr.'s Boom Bunker

World 6

 * Melty Monster Galaxy
 * Clockwork Ruins Galaxy
 * Throwback Galaxy
 * Battle Belt Galaxy
 * Flash Black Galaxy (Hungry Luma)
 * Slimy Spring Galaxy
 * Bowser's Galaxy Generator

World S

 * Mario Squared Galaxy
 * Rolling Coaster Galaxy
 * Twisty Trials Galaxy
 * Stone Cyclone Galaxy
 * Boss Blitz Galaxy
 * Flip-Out Galaxy (Hungry Luma)
 * Grandmaster Galaxy

Trivia

 * In both Super Mario Galaxy and Super Mario Galaxy 2, galaxies are commonly represented by three-dimensional revolving icons which consist of either one planet found in the galaxy or multiple planets in the galaxy (in Super Mario Galaxy, only 29 of the 42 total galaxies in the game have revolving icons, as the other 13 remaining galaxies are accessed outside of one of the six main domes).
 * Note that in Super Mario Galaxy, every object found on the revolving galaxy icons remains stationary. In Super Mario Galaxy 2, however, almost every galaxy icon in the game has something moving on it.