Two projections of the Sun’s orbit on the X–Y plane, calculated with M _bar = 1 × 10⁹M_⊙ (red) and M_bar = 3 × 10¹⁰M_⊙ (blue), over 5 Gyr; all other parameters are taken from Table 1. The initial position of the Sun is shown by a blue cross. For the smaller bar’s mass, the Sun’s trajectory oscillates around the L₄-centre, while, for the larger mass, it oscillates around the B₁-centre. The zone of influence of the bar/bulge and the loci of the spiral arms are shown by black curves.