Lecture 1: What are the Stars ?
This first lecture takes us through the early evolution of Astrophysics when amazing discoveries began to take place through scientist's efforts to explain celestial observations using known laws of physics.
This lecture begins with the reason for the "limb darkening" of the Sun, and the discovery of Helium in the Sun. It then explains the late 19th century ideas on "Stars as globes of gas", supported against gravity by the pressure of the gas. The equation of "hydrostatic equilibrium" is derived.