A word of caution
The sections of "Stargazers" covering the Sun was an afterthought. The rest of the material was mostly complete when a teacher of astronomy, adapting the material for his course, pointed out an omission. "How can I give them astronomy and not discuss the electromagnetic spectrum?" All our information about stars, he noted, comes to us as light or other electromagnetic radiation.
Yes, indeed--and therefore this part was added. If you, dear reader, are engaged in a personal voyage of discovery, dig right in. You will find many interesting subjects, and your only limitations will be your own time and your own patience.
However, if you are a teacher presenting a class in astronomy, you are only given a limited time. Even without optional sections, "Stargazers" contains more than can be presented in one school year. You are therefore advised to cover either Newtonian mechanics or the sections on the Sun that follow here, but not both.
A class stressing astronomy may skip mechanics. Newton's law of gravitation will then be missed, as will be some interesting applications such as weightlessness in space. However, almost all the material on the Sun fits seamlessly into the sections that precede it or follow it, and lesson plans have been provided for sections #S-1 to #S-7 as well. If your class stresses physics, you might prefer to cover mechanics and omit (or skim) the parts on the Sun, which are less mathematical, although they also cover interesting areas of physics.
What is covered here (mainly for teachers)
Astronomy is often the stepchild subject in high school. Usually taught as an elective subject, much of its material is memorized from textbooks or from the teacher's description, based on scaled-down college material. It is difficult for students to do much in astronomy class, since stars are only seen at night, and the tools of the astronomer are usually beyond the reach of a high school student, in more ways than one.
This part of "Stargazers" develops a novel approach, using the Sun as the key to the astronomical universe. That key opens many other doors as well: to the weather and the atmosphere (section #S-1), to magnetism (#S-3), to the study of spectra (#S-4), to the notions of electromagnetic waves and photons (#S-5), to X-rays (#S-6) and to the atomic nucleus (#S-7). This part may therefore is studied not just for what it tells about the Sun, but also as an introduction to subjects of modern physics.
In compiling educational material, it is all too easy to get carried away and add interesting but optional material. And this particular writer is so easily tempted! Section #1 was therefore extended to a 3-section discussion covering aspects of the processes driving weather and climate. Section #S-7 also contains ideas on the evolution of stars, e.g. supernovas and their remnants, including black holes. Later, when compelling evidence emerged about the black hole at the center of our galaxy, a section dealing with that exotic subject was also added.
Also, since the student has already been introduced to nuclear physics, an additional section #S-8 was added about nuclear power generation. That subject is of great public interest and concern, but so far, it seems, a concise but explicit introduction has not been available. Maybe this will fill the need! Still later a section on nuclear weapons was also added, a reluctant concession to reality.
Brief optional sections were added during the writing of the lesson plans: on the three-color theory of vision (#S-4A; an easier approach was later found and is cited), on the interplanetary magnetic field (#S-6A) and on the history of atomic and nuclear theory (#S-7A). The first two contain hands-on exercises.
Enough of this introduction. Go to it, and discover!