Positions of the spacecraft and the shock nose direction in the ecliptic plane at 20:55 UT on 23 July 2012, the time when the shock passed STEREO-A. The red and blue spirals depict respectively magnetic field lines of Parker passing through STEREO-A which was at W121.3, 0.96 au and STEREO-B which was at E115.2, 1.02 au. The black spiral solid line represents magnetic field line of Parker passing through ACE which was at W0, 1 au. The black straight line points to the direction of shock nose, which was at W133. The yellow area shows the outline of the shock width W_s, which is set to 230°.