Sun & stellar structure

Much of what is known about the stars comes from studying the star closest to us, the Sun. At a distance of almost 150 million kilometers, the Sun is a few hundred thousand times closer to us than the next nearest star. Because of its proximity, astronomers are able to study our star in much, much greater detail than they can the other stars.
The Sun is a G2-type main sequence star that has been shining for almost 5 billion years. It is known from radioactive dating of the Earth, Moon, and meteorites, that these objects have been around for about that length of time and temperatures on the surface of the Earth have been pleasant since it formed. The Sun's energy has made this possible. What could power something as big as the Sun for so long? The process called nuclear fusion is now known to be the source of the Sun's enormous energy, as well as, other stars. This is a relatively recent discovery. However, using simple physical principles of gas physics, astronomers knew about the density and temperature structure of the interior of the stars long before they unlocked the secret to what could power them for so long. This chapter will cover these topics. I will first give a brief description of the Sun to give you an idea of what a star is like and then go into the basic principles of what the interiors of stars are like and what powers them. The vocabulary terms are in boldface.