Radius evolution of a 1.2 M_⊙ nonmagnetic Dartmouth stellar-evolution model mass track (solid red line). This is shown with (top) the luminosity evolution of the p-p chain (solid black line) and CNO cycle (dashed black line) as a fraction of the total stellar luminosity and (bottom) the evolution of the central abundance of ³He, ¹²C, and ¹⁴N. Vertical lines denote the start and end of the first fusion bump.