In reality., stars are not perfect blackbodies, and so their emitted spectra don’t depend solely on temperature, but instead contain detailed signatures of key physical properties like elemental composition. For atoms in a gas, the ability to absorb, scatter, and emit light can likewise depend on the wavelength, sometimes quite sharply. We find that the discrete energies levels associated with atoms of different elements are quite distinct. We introduce the stellar spectral classes (OBAFGKM).

This book critically examines the following claim: Self-interest is the problem; it is also the only possible solution. The problem with what? The solution to what? This is a book about American government and politics, and both the problem and the solution are concerned with how best to conduct our politics. The title to this introduction states a paradox: The thing that causes the predicament – self-interest – also gets us out of it. To put it more precisely (and optimistically): All that is required in a well-ordered political system for the public good to be achieved is for everyone – politicians, citizens, leaders of special interest groups – to pursue their own selfish interests. The political system does not require anyone to set aside his or her interests in the name of the public good for that good to be achieved. We describe in detail the source of this claim in Chapter 2 and devote the rest of the book to some critical questions about whether the claim that self-interest is sufficient to resolve the problems it creates in politics fits with the reality of American politics today.

Setting aside Donald Trump’s typical braggadocio, when he claimed he alone could fix the mess that was America after eight years under Democratic President Barack Obama, he was following a long-standing political tradition in at least two ways: Presidential candidates from the party not currently in power emphasize what is wrong in American national life, not what is going well, and presidential candidates of both parties promise more than they can deliver. Whether it was Jimmy Carter promising independence from foreign oil, Ronald Reagan promising to balance the budget, cut taxes, and increase spending on the military, or Barack Obama promising healthcare reform that would require little inconvenience or change from those satisfied with their insurance coverage, presidential candidates assume the mantle of responsibility for the nation’s well-being well beyond their constitutional capacity to deliver.

As a star ages, more and more of the hydrogen in its core becomes consumed by fusion into helium. Once this core hydrogen is used up, how does the star react and adjust? Stars at this post-main-sequence stage of life actually start to expand, eventually becoming much brighter giant or supergiant stars, shining with a luminosity that can be thousands or even tens of thousands that of their core hydrogen-burning main sequence. We discuss how such stars reach their stellar end-points as planetary nebulae or white dwarfs.

Before beginning in earnest our exposition of Madison’s Republic in the next chapter, we spell out some key concepts and questions that help to give context to the next chapter and the rest of the book. We discuss concepts such as the meaning of democracy, the principal–agent problem, and collective action because these concepts relate directly to an understanding of how theories relate to the world of politics. We also introduce basic ideas about how political scientists approach the study of politics especially by using models that simplify some important aspect of the political world under study.

This chapter considers stellar ages. Just how old are stars such as the Sun? What provides the energy that keeps them shining? And what will happen to them as they exhaust various available energy sources? We show that the ages and lifetimes of stars like the Sun are set by long nuclear burning timescales and the implications that high-mass stars should have much shorter lifetimes than low-mass stars.

Mass is clearly a physically important parameter for a star, as it will determine the strength of the gravity that tries to pull the star’s matter together. We discuss one basic way we can determine mass, from orbits of stars in stellar binaries, and see the range of stellar masses. This leads us to the Virial Theorem, which describes a stably bound gravitational system.

As a basis for interpreting observations of binary systems in terms of the orbital velocity of the component stars, we review the astrometric and spectrometric techniques used to measure the motion of stars through space. Nearby stars generally exhibit some systematic motion relative to the Sun, generally with components both transverse (i.e., perpendicular to) and along (parallel to) the observed line of sight.

We conclude our discussion of stellar properties by considering ways to infer the rotation of stars. All stars rotate, but in cool, low-mass stars such as the Sun the rotation is quite slow. In hotter, more-massive stars, the rotation can be more rapid, with some cases (e.g., the Berillium stars) near the “critical” rotation speed at the star’s surface.

Hubble’s law gives us the simple and obvious interpretation that we currently live in an expanding universe. The inverse of Hubble’s constant defines the “Hubble time,” which effectively marks the time in the past since the expansion began. More realistically, one would expect the universe expansion to be slowed by the persistent inward pull of gravity from its matter. We consider how various theoretical models for the universe connect with the observable redshift that indicates its expansion.