For comparison, the true stars of different luminosity necessary to calculate the magnitude that would have each star, if it were at the same distance from the solar system. For convenience, the standard distance of 10 parsecs was chosen. The size of the star, the observed at this distance is called the absolute magnitude (M). The absolute magnitude can be calculated from the apparent magnitude. Calculations are based on the principle that the intensity of light from a point source at a certain distance in relation to changes inversely proportional to the square of the distance. This principle implies that the light intensity varies in a ratio (d / 10) 2 when moving from the distance d to 10 parsecs from the star. ? If Dm is the corresponding difference magnitude, then 100 m / 5 = (d / 10) 2 Using a scale of decimal logarithms, we obtain the equation m = 5 log d - 5?; hence, m = M + 5-5log d (where 5 - the absolute value of the Sun).