Everything I've ever read about Helioseismology suggests that it is about constructing extraordinarily complex models about the dynamics of plasmas (gasses that are so hot that their electrons are not generally bound to nuclei) and the transport of heat from the Sun's core to its outermost layers, and testing the predictions of those models against the sounds that we see (through doppler shift) on the Sun's surface. Much of Astrophysics is about trying to make detailed models about things that we can't really observe directly, and there are times when it's natural to wonder if there is any way that we will ever really know if these theoreticians aren't simply deluding themselves about what they think they know.
Helioseismology has been one of those areas where I've found myself wondering just what we really know from all this theory; But, then, I read Chapter 8. At the end of that chapter, the author talks about a process of using sound waves that travel from the far side of the Sun to the near side, and using them to construct images of the far side. Those images can be used to predict when and where Sunspots will appear when corresponding patches of the Sun's surface rotate into view. And the accuracy of these predictions depends on the correctness of the conclusions they've drawn about deeper structure within the Sun. The data are course and subject to some changes that can occur during the 10 days or so that it takes for the imaged regions to rotate from the far side into full view, but on the whole they offer a rather concrete confirmation of a lot of the theory in this relatively young branch of Astrophysics.
We live in truly remarkable times.