Extended outer atmosphere of the Our parent star. The structure of Sun's interior is the result of the hydrostatic equilibrium between gravity and the pressure of the gas. The interior consists of three shells: the core, radiative region, and convective region. Image source: http://eclipse99.nasa.gov/pages/SunActiv.html. The core is the hot, dense central region in which the. The glow of the corona is a million times less bright than that of the Point where a star's atmosphere appears to become completely opaque. Thus, the photosphere may be thought of as the imaginary surface from which the starlight that we see appears to be emitted. The photosphere is not a thin surface; the Sun's photosphere has a thickness of ~100 km. (Within that Click on Term to Read More; it can only be seen when the disk of the Sun is blocked during a total solar Obscuring of one celestial body by another, either by direct superposition or by the casting of a shadow. Solar eclipses are of three kinds, total (when the Moon completely eclipses the Sun), annular (when a complete ring of sunlight escapes around the edge of the Sun), and partial. Lunar eclipses Click on Term to Read More, or by using a coronagraph, which artificially blocks the disk of the Sun so that it can image the regions surrounding the Sun. The corona is very hot as indicated by emission lines corresponding to very highly ionized atoms (e.g., Fe16+). Such highly ionized atoms can only be produced at temperatures in the 106 degree range. The extremely high temperature of the corona is thought to due to the solar magnetic field, which can store and transport energy from lower regions of the Sun to the corona. However, the details of how this heating takes place are not yet fully understood.
Some or all content above used with permission from J. H. Wittke.