The Sun may be described as a globe of gas heated to incandescence by thermonuclear reac-tions from within the central core.

The main body of the Sun, although com-posed of gases, is opaque and has several distinct layers. (See fig. 1-2-1.) The first of these layers beyond the radiative zone is the convective zone. This zone extends very nearly to the Suns surface. Here, heated gases are raised buoyantly upwards with some cooling occurring and subsequent convective action similar to that which occurs within Earths atmosphere: The next layer is a

Figure 1-2-1.One-quarter cross-section depicting solar structure.

 well-defined visible surface layer referred to as the photosphere. The bottom of the photosphere is the solar surface. In this layer the temperature has cooled to a surface temperature of 6,000K at the bottom to 4,300K at the top of the layer. All the light and heat of the Sun is radiated from the photosphere. Above the photosphere is a more transparent gaseous layer referred to as the chromosphere with a thickness of about 1,800 miles (3,000 km). It is hotter than the photo-sphere.

Above the chromosphere is the corona, a low density high temperature region. It is extended far out into interplanetary space by the solar winda steady outward streaming of the coronal materiai. Much of the electromagnetic radiation emissions consisting of gamma rays through x-rays, ultraviolet, visible and radio waves, originate in the corona.

Within the solar atmosphere we see the occurrence of transient phenomena (referred to as solar activity), just as cyclones, frontal systems, and thunderstorms occur within the atmosphere of Earth. This solar activity may consist of the phenomena discussed in the following paragraphs which collectively describe the features of the solar disk (the visual image of the outer surface of the sun as observed from outside regions). (See fig. 1-2-2.)

Privacy Statement - Press Release - Copyright Information. - Contact Us - Support Integrated Publishing