Passage VI

A star's brightness is described by its magnitude. As magnitude increases, brightness decreases. A star's apparent magnitude is measured from Earth. A star's absolute magnitude is the magnitude that would be measured 10 parsecs from the star (1 parsec [pc] = 3.1 x 10¹⁶ m). V represents the apparent magnitude of a star's visible light. M_V and M_B represent the absolute magnitudes of a star's visible light and blue light, respectively.

Table 1 lists V, M_V, V - M_V, and M_B - M_V for particular stars in each of 4 hypothetical star clusters (SCs). Figure 1 shows SC age versus M_B - M_V. Figure 2 shows SC distance from Earth versus V- M_V. Table 2 lists a star's power output of visible light for a given M_V.