The figure below shows the sizes of red giant stars compared to the Sun. Using the Kepler telescope, we have detected oscillations in hundreds of red giant stars. The periods of those oscillations allowed us to study the interiors of these giant stars, which represent the future life of our Sun.
The figure below shows the stages in the evolution of a star like the Sun. The Sun itself is currently fusing hydrogen into helium in its core (lower left). In later stages, when it becomes a red giant, the star will fuse hydrogen in a shell around the helium core (2nd and 3rd figures). Finally, the red giant will begin to fuse helium into carbon in its core (4th figure).
Click to listen to the red giant concert. This audio file was made by Daniel Huber, a PhD student at the University of Sydney. You will hear oscillations based on actual frequencies that were measured by the Kepler mission, sped up so as to be audible to the human ear. Starting with the sound of a small red giant you will gradually hear three stars of increasing size - each with lower frequencies, but higher amplitudes - entering the "red giant concert"
Click to see Computer animations by Paul Beck (K.U. Leuven, Belgium) showing mixed modes in red giants.