This chapter presents some basic calculations that show counterintuitive or unexpected results. First, it is shown that the Planck spectrum of light, which played an important role in the history of quantum mechanics, doesn’t say anything about the existence of indivisible particles. Second, a brief discussion of “chaos theory” shows that jumpy and unpredictable behavior can occur in classical systems. Last, the concept of “entanglement” is introduced as a basic property of quantum systems.

The chapter describes the physical properties and important processes of the Sun’s interior, surface, and atmosphere including the physics of heat transfer and electromagnetic radiation. The different features of each of the main solar regions (core, radiative zone, convective zone, photosphere, chromosphere, and corona) are described and illustrated. The learning tool called concept mapping is described and used to highlight how to frame ideas, physical concepts, and systems into a graphical organizational manner to help assess understanding.

Following directly the from the previous chapter, we see that in addition to a shift toward shorter peak wavelength, a higher temperature also increases the overall brightness of blackbody emission at all wavelengths. This suggests that the total energy emitted over all wavelengths should increase quite sharply with temperature. We introduce the Stefan–Boltzmann law, one of the linchpins of stellar astronomy.

There are no restrictions on how many bosons can occupy a single particle state, which has important consequences for their thermodynamic behaviour.Photons, quanta of the electromagnetic field, can be viewed as bosons with zero chemical potential, which allows the derivation of the thermodynamic properties of blackbody radiation, including the Stefan--Boltzmann Law.Non-interacting bosons with non-zero chemical potential can exhibit Bose--Einstein condensation at low temperatures, and interacting bosons may form a superfluid state.Low energy excitations in materials -- lattice vibrations (phonons) and spin waves (magnons) -- also behave as bosons, and are important for understanding the specific heat of materials at low temperatures.Of particular note is the Debye model which gives a simple account of the contributions of phonons to specific heat.