The sun is a star, just like the other stars we see at night. The difference is distance -- the other stars we see are light-years away, while our sun is only about 8 light minutes away -- many thousands of times closer.
Officially, the sun is classified as a G2 type star, based on its temperature and the wavelengths or spectrum of light that it emits. There are lots of G2s out there, and Earth's sun is merely one of billions of stars that orbit the center of our galaxy, made up of the same substance and components.
The sun is composed of gas. It has no solid surface. However, it still has a defined structure. The three major structural areas of the sun are shown in the upper half of Figure 1. They include:
- Core -- The center of the sun, comprising 25 percent of its radius.
- Radiative zone --The section immediately surrounding the core, comprising 45 percent of its radius.
- Convective zone -- The outermost ring of the sun, comprising the 30 percent of its radius.
Above the surface of the sun is its atmosphere, which consists of three parts, shown in the lower half of Figure 1:
- Photosphere -- The innermost part of the sun's atmosphere and the only part we can see.
- Chromosphere -- The area between the photosphere and the corona; hotter than the photosphere.
- Corona -- The extremely hot outermost layer, extending outward several million miles from the chromosphere.
All of the major features of the sun can be explained by the nuclear reactions that produce its energy, by the magnetic fields resulting from the movements of the gas and by its immense gravity.
It begins at the core.