Geometry of the Sun and representation of the velocity vectors related to the filament eruption. The axes (${\widehat{\mathit{e}}}_x,{\widehat{\mathit{e}}}_y,{\widehat{\mathit{e}}}_z$) define the Cartesian coordinate system (observer’s reference frame), while (${\widehat{\mathit{e}}}_{\mathrm{\Phi }},{\widehat{\mathit{e}}}_{\mathrm{\Theta }},{\widehat{\mathit{e}}}_n$) determine the local coordinate system (local reference frame) fixed at point F (see the text). P indicates an instantaneous position of the filament used to describe the trajectory of the eruption in 3D space, which is presented in Fig. 12. The arrows labeled υ_pos, υ_los, and υ_true denote the plane of sky, line of sight, and true velocities, respectively. The angle of the eruption subtended to the Sun-Earth line is given by δ, whereas the inclination angle of the eruption with respect to the local solar normal ${\widehat{\mathit{e}}}_n$ is denoted by ϑ.