RED GIANTS

The Sun looks the same to us, unchanging, day after day. A simple observation, however, tells us that it is evolving and must be changing in some manner. That observation is just the warmth on our upturned faces on a sunny day. The radiation that flows from the Sun carries energy out into space. There is nothing from space replacing that energy. The Sun must, therefore, be losing energy overall. Something must be going on within the Sun that is slowly, inevitably altering it. The lesson from Chapter 1 is that the change in the Sun involves its composition. The Sun is irrevocably transmuting some of its hydrogen into helium. That transformation cannot be undone. The alteration of the structure of the Sun is slow, but it is steady. Eventually, the changes will be drastic.

As remarked in Chapter 1, the hydrogen burns only in the center of a star, where the temperatures are highest. That means that the central region is where the hydrogen is consumed and the helium builds up. Even when the hydrogen is fully transformed in the central region, the outer, cooler portions of the star will not have burned. They retain their original composition. This causes the star to become schizoid and to do two things simultaneously: shrink and swell. This development is in strict accord with the principle of conservation of energy, but the application of this principle is more complex than for stars with a homogeneous composition.