The Preppendix of the Omnidoxy is the pre-disquisitional segment of the Omnidoxy that constitutes a significant portion of the entire text as part of the Original Omnidoxical Series as solely written and authored by Cometan and published by the Astronist Institution. The segment that forms the majority of the Preppendix is known as the Astronicon which is an extensive collection of mythological narratives that came to form the foundations of Astronist mythology.
 
Additionally, the Preppendix also consists of a series of very short subsegments that introduce the Omnidoxy text, provide important background information to the treatise, and even explore some key ideas that have become important to wider Astronism.
 
However, the most important and dominant part of the Preppendix, as aforementioned, is the Astronicon which encompasses an epic story of space mythology in which the family of Cometan are set on a course of astronomical distances to reach the astronomical elixir and to attain the long sought-after state of cosmosis. The Astronicon is the principal introducer of the world to the beautiful and rich tradition of storytelling within the Astronist religion and as a result, also introduces Astronist mythology to the world, the body of works, characters, and themes that are part of the wider Astronic tradition of mythology.