Schematic diagram of Cygnus X-1. The orbital phase φ = 0 corresponds to the superior conjunction of the compact object. The orbit of the BH is indicated by the ellipse with an eccentricity of 0.018 (Orosz et al. 2011). Neither the inclination of the orbit with the line of sight nor the longitude of the ascending node were considered. The stellar radius, assumed to be 16.4 R_⊙, and the periastron phase and argument were taken from Orosz et al. (2011). AU stands for astronomical unit.