What is the principle governing star labeling in the astronomical magnitude system?

Smaller magnitude numbers indicate brighter stars.

The astronomical magnitude system is inherently counter-intuitive for newcomers because it operates inversely to standard measurement scales. A star assigned a smaller numerical magnitude value, such as magnitude 1, is significantly brighter than a star assigned a larger number, such as magnitude 2. This inverse relationship extends further, as objects of extreme brightness, like the Sun or the full Moon, possess negative magnitude values, signifying their overwhelming luminosity when viewed from Earth. This convention originated with the ancient Greek astronomer Hipparchus, who designated his brightest observed stars as first magnitude and the faintest visible stars as sixth magnitude, establishing the rule that lower numbers corresponded to greater observed brightness, a foundational concept retained even in the modern, refined quantitative scale.