Self-reference is a concept that involves referring to oneself or one’s own attributes, characteristics, or actions. It can occur in language, logic, mathematics, philosophy, and other fields.
The magnitude scale dates to before the ancient Roman astronomer Claudius Ptolemy, whose star catalog popularized the system by listing stars from 1st magnitude (brightest) to 6th magnitude (dimmest). The modern scale was mathematically defined in a way to closely match this historical system.