1. The brightness that a star would have if it were at a distance of 10 parsecs in perfectly clear space without interstellar absorption. Absolute magnitude is usually deduced from the visual magnitude measured through a V filter, and is then written M_V. If defined for another wavelength it carries a different subscript (U, B, etc.). When radiation at all wavelengths is included it becomes the absolute bolometric magnitude, M_bol. The Sun has an absolute magnitude of +4.8. Most other stars range between −9 (supergiants) and +19 (red dwarfs).

2. The brightness that a Solar System body would have if it were at a distance of 1 au from both the Sun and Earth and fully illuminated by the Sun (i.e. with a phase angle of 0°).