We will begin our work on stars by studying the one we know best: our Sun. The Sun is the closest star. Unlike every other star, it is so close that we can minutely observe its surface and surrounding layers.

We owe our existence to the Sun. Its great emissions warm us, and protect us from the unimaginable cold of interstellar space. Indeed most of the Universe, far from the Sun or other stars, is just a few degrees above absolute zero, which is 459 degrees below zero Fahrenheit. We lie huddled close to a warming campfire in a frigid wasteland.

As we have noted, the Sun is gigantic – more than a hundred times the size of the Earth – and immensely massive – far more massive than all the planets of the Solar System combined. And it is so hot as to vaporize every known substance. We might say that the Sun is nothing more than a ball of superheated gas. But perhaps we should put quotation marks around that “nothing more.” As we will see, this blazing sphere of gas exhibits a rich and complex behavior.

In this chapter we will discuss the outer regions of the Sun: the Sun that we can see. In Chapter 14 we will turn our attention to the Sun that we cannot see: its deep interior.