Introduction

At the beginning of §2.4, we pointed out the scope of the subject stellar interior. It appears from observational data (to be discussed in detail later) that various quantities pertaining to stars have some relations amongst each other.For example, a more massive star usually has a higher luminosity and also a higher surface temperature. To explain such observed relations theoretically, we have to figure out the equations which should hold inside a star and then solve them to construct models of stellar structure.

The years ≈1920–1940 constituted the golden period of research in this field, when theoretical developments led to elegant explanations of a vast mass of observational data pertaining to stars. Ever since that time, the subject of stellarinterior or stellar structure has remained a cornerstone of modern astrophysics and improved computational powers have ledto more detailed models. This is a subject in which theory and observations are intimately combined together to build up an imposing edifice. While presenting a subject like this, the first question that a teacher or a writer has to face is this: from a purely pedagogical point of view, is it better to start with a discussion of observational data or with a discussion of basic theoretical ideas?

It follows from simple theoretical considerations that there must be objects like stars, provided energy can be generated by some mechanism in the central regions.