Astrotheory was a sub-discipline of astronomy in which one hypothesized about astronomical phenomena. One who practiced it was known as an astrotheorist. (VOY: "Alter Ego")
Starfleet Academy taught astrotheory in at least one class, Astrotheory 101. (VOY: "Future's End")
In 2373, while observing an inversion nebula, Kathryn Janeway remarked on its pleasing appearance, saying "Astrotheory never predicted this would be so lovely. Beauty and mystery, a tantalizing combination." (VOY: "Alter Ego")