Figure 20-6: Further Stages in the Evolution of the Sun This diagram, which shows how the luminosity of the Sun (a 1-M_⊙ star) changes over time, is an extension of Figure 19-8. We use different scales for the final stages because the evolution is so rapid. During the AGB stage there are brief periods of runaway helium fusion, causing spikes in luminosity called thermal pulses.

(Adapted from Mark A. Garlick, based on calculations by I.-Juliana Sackmann and Kathleen E. Kramer)