It is a great pleasure and privilege to give the opening lecture at this IAU Colloquium “Inside the Stars”. It is particularly appropriate that it is held in Austria, the country of Ludwig Boltzmann whose name will appear explicitly or implicitly in every lecture.
My task is to describe the astrophysical and cosmological setting within which our discussions will take place. I emphasise that I am an outsider at this colloquium in all possible senses. My own research interests are in the areas of high energy astrophysics, extragalactic research and astrophysical cosmology. In lecturing to my students, however, I emphasise that the subject of the present colloquium is at the very heart of virtually all astrophysics and these studies are quite essential in order to make sense of galaxies and extragalactic systems. If we did not have this confidence in our ability to understand the stars, at least in principle, we would worry about the reliability of the enormous astrophysical edifice which has been built up to explain the large scale features of our Universe. I also emphasise to my students that the study of the stars is among the most exact of the astrophysical sciences — in my enthusiastic moments, I claim that, in the very best of these studies, astrophysics approaches the precision of laboratory experiment. I hope to find many examples this week to reinforce this belief.
From my perspective, what I need is a User’s Guide to Stars and Stellar Evolution, in other words, a reliable set of rules about the origin and evolution of stars in order to diagnose the physical properties of the systems I am trying to understand. I will illustrate the types of information we need by discussing three case studies in the areas of (i) high energy astrophysics, (ii) classical cosmology and (iii) astrophysical cosmology and the origin of galaxies. Necessarily, these studies will be far from complete, but I hope they will illustrate some of the issues which come up in these disciplines. In the course of the discussion, it will become apparent that I will touch upon essentially all branches of contemporary astrophysics. I will take very different approaches to the three case studies.