Astronomical magnitude

Astronomical magnitude is a logarithmic measure of the brightness of an astronomical source; a smaller magnitude denotes a brighter source.

Apparent magnitude measures how bright an astronomical source appears to an observer.

Absolute magnitude is the apparent magnitude that an astronomical source would have at a conventional reference distance. It separates intrinsic luminosity from distance-dependent dimming.

The distance modulus is the difference between apparent magnitude and absolute magnitude. For distance $d$ in parsecs,