Hundreds of thousands of compute stars ride nested elliptical orbits whose long axes precess with radius, so the crowding of their apocentres traces two coherent, trailing spiral arms — a particle rendering of density-wave theory. Stars stream along their orbits at a differential rate while the arm pattern turns slowly; a warm bulge blooms at the core with blue young stars and pink H II knots picking out the arms. Press to morph spiral → barred → elliptical, drag to tilt the view, scroll to dolly in.