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What's in the Sun?

The physicist Artur Eddington once said he hoped one day science would have advanced far enough to understand "so simple a thing as a star."

As scientists study our own sun, Eddington's dream of at least understanding one star is getting closer to reality, but the task is a more complex one than it may seem.

For example, from here on earth, the sense we get of the sun is largely homogeneous. The sun appears as an intensely bright ball of fire, without much detail. In this respect, it appears rather simple.

Modern investigations, however, have shown our "common sense" image to be superficial. Far from being homogeneous, the sun in fact has several interior layers, each concealing the next like skins on an onion.

The round, bright surface we see is called the "photosphere," because it is the part of the sun that emits light. If we could peel the photosphere back we would find a bubbling, churning layer underneath it known as "the convection zone." This part of the sun resembles boiling water: hot gases are racing to the surface and cooler ones being submerged all the time, making for a layer of bubbling fluid.

Underneath the convection zone lies "the radiative zone." This area is not soupy like the convection zone, but is more like a wall of radiant energy pressing outward from the core. The core itself forms the final piece of the sun, where the fundamental nuclear reactions are taking place that keep our star burning.

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