The goal of this course is to undertake a quantitative examination of the physical structure of the
Sun. The text is aimed at upper-level physics undergraduates and at graduate students in their early
years of graduate study. To achieve our goal, we explore how various laws of physics can be used
to help us derive realistic information about different regions in the Sun. Although the material that
makes up the Sun is gaseous throughout its volume, the physical conditions change dramatically
from one part of the Sun to another: e.g., the gas pressure changes by some 12 orders of magnitude
between center and “surface”. As a result, different aspects of physics are found to be dominant in
different regions. For someone who is interested in physics, the Sun provides a “real world” laboratory in which to test a broad range of topics, including fluid flow, heat transport, thermodynamics,
radiative transfer, quantum mechanics, nuclear physics, plasma physics, and turbulence. Of special
interest is the fact that the Sun presents us with striking examples of magnetohydrodynamic (MHD)
processes, i.e., the interactions that occur between fluid flows and electromagnetic fields. In the
later chapters of this book, we shall discuss how the Sun displays evidence for an array of MHD
processes: specifically, in certain regions, the fields control the motions of the gas, whereas in other
regions, the gas controls the motions of the field.