Caption: Cartoon of a stellar structure model (i.e., interior stellar structure model) of the Sun (CK-263) showing the "runs" (i.e., distributions) of interior luminosity, interior mass, density, and temperature as functions radius in units of the solar radius R_☉ = 6.957*10**5 km = 109.1 R_⊕ = 4.650*10**(-3) AU.

Features:

1. Stellar structure models must be calculated using numerical methods on the computer from the 4 equations of stellar structure. There are NO analytic solutions.

2. Usually, for stellar structure models the boundary conditions for density and temperature are set to zero since they are so small that are negligible for the interior structure and can only be determined to any accuracy/precision by a stellar atmosphere model in any case.

3. Below is a table illustrating the center-to-surface variations in Sun quantities radius, interior luminosity, interior mass, density, temperature, and pressure. The surface values are determined by stellar atmosphere models.

   _________________________________
   Table:  Center and Photosphere 
           Quantities of the Sun
   _________________________________
             Center     Photosphere
   _________________________________
   
   R (m)       0        6.96*10**8
   
   L (W)       0        3.828
                          *10**26
   
   M (kg)      0        1.98855
                          *10**30
   
   Density   150        2.18
                          *10**(-7)
   (g/cm**3)
   
   T (K)     15.7       5772
                *10**6
   Pressure   2.33      0.827
   (Earth       *10**11
   atmos-
   pheres)
   _________________________________

   References: Cox-342, Wikipedia: Sun.

   _________________________________

4. As one can see from the table above and the plots, there are vast center-to-surface variations in Sun quantities.

   In particular, the pressure at the Sun's center is huge as it must be to hold up the Sun against the force of gravity acting on the Sun's own mass (i.e., against the Sun's self-gravity) and trying to collapse Sun.

   Note that only the pressure force can support astronomical objects against their own self-gravity for astronomical objects more massive than a small asteroid and unsupported by kinetic energy.

5. The Sun's surface temperature (i.e., photospheric temperature) in the above table is determined by Wien's law by approximating the Sun as black-body radiator. Reversing the calculation, one finds the solar spectrum maximum is

     λ_max = 2897.7685(51) micron-K / 5772 K
   
          ≅  0.5015 microns
                    which is in the visible range 0.4--0.7 microns.  

   The maximum is, in fact, in green light, but the psychophysical response to sunlight is what we call white light (see HyperPhysics: Color).