Celestian is a non-binary gender from the galactian alignment system. It is the demigender version of stellarian meaning it only has a partial connection to stellarian, with the other part being something else. The "other part" can be another galactian alignment or it can be another unrelated gender. The ‘other part’ can not be singularian, as singularian can only exist by itself.
The term celestian was first coined by Tumblr user Kaispiral in a reply to the post on the blog ask-pride-color-schemes that first coined the terms dawnian and duskian. They later made the celestian flag on DevientArt under the username Mikokit.