Simplify the following text for a Grade 12 native English-speaking person.
Original: His other reputed achievements include the discovery of Earth 's precession , the compilation of the first comprehensive star catalog of the western world , and possibly the invention of the astrolabe , also of the armillary sphere , which he used during the creation of much of the star catalogue .
Simplified: His other well-known achievements include the discovery of precession , the compilation of the first comprehensive star catalog of the western world , and possibly the invention of the astrolabe . He might also have invented the armillary sphere which first appeared during his century and was used by him during the creation of much of the star catalogue .