The Sun Is a Gas

Abstract

The sun is a ball of gas—a special kind of gas to be sure. It is so hot in some regions in the interior that the atoms have come apart completely to form a state of matter known as a plasma—an electrically charged gas. To understand the physical processes that cause stars, like the sun, to shine and to understand how and why stars evolve, we must learn something about the behavior of gases. A quantity that is quite useful in describing the state of a fluid (gas or liquid) is the pressure. We define the average pressure p ona small area ΔA in a fluid as (ΔF)⊥, the component of the force exerted perpendicular to the area, divided by the area,