Table 780 

 SOLAR DATA 



613 



Quantitative Estimates of Composition of Solar Atmosphere 



(Taken from Russell, Astrophys. Journ., 70, II, 1929.) 



In the chromosphere a deep layer of gases is held up by radiation pressure. The (gas) pressure, p, and 

 density, d, increase slowly downwards as gravity gradually balances the radiation pressure. At the base p 

 may be about 10 7 atmosphere. At lower levels is the reversing layer in which gravity is dominant, p 

 increases rapidly, and temperature remains nearly constant at 5000 K., as long as the gases are trans- 

 parent. When p < 0.01 atm. general absorption by electron collisions make gas hazy. Opacity gains 

 greatly with p, passes rapidly to the photosphere. When opacity important, temperature rises (radiative 

 equilibrium, Schwarzschild, Eddington). Observed photospheric temperature = mean value of the 

 radiating layers (Russell, Stewart, Astrophys. Journ. 59, 197, 1924). 



The presence and absence of lines of different elements depends on the excitation potential. Almost 

 all the elements for which this is less than 5 volts appear. There are very few other lines except the strong 

 ones of H. The level of ionization in solar atmosphere is such that those of 8.3 volts are 50% ionized. 



Na, Mg, Si, K, Ca, and Fe are 95% of the whole mass. Number of metallic atoms above cm 2 of surface 

 = 8 X io 20 . 80% are ionized. Mean atomic weight = 32, total mass 42 mg/cm 2 . Even atomic weights 

 10 times as abundant as odd. Heavy metals (Ba onwards) little less abundant than those beyond Sr. 

 Hypothesis that heavy metals sink below photosphere thus not confirmed. Metals Na-Zn far most 

 common. Most elements not appearing in the table would hardly be expected to show spectral lines under 

 solar conditions. 



Nonmetal abundance difficult to estimate. O is as abundant by weight as all metals together. Atmosphere 

 = 60 H by vol., 2 He, 2 0, 1 of metallic vapors, 0.8, free electrons. Temperature of reversing layer = 

 5600 K.; pressure at its base 0.005 atm. 



In the following table, S Q = whole no. neutral atom/cm 2 ; Si, no. ionized; T, total no. both stages of 

 ionization; Q, total mass/cm 2 = T X at. wt. :, ::, indicate less accuracy; ?, origin doubtful. 



Comparison of above values with values of Payne by a very different process show good agreement 

 except for H (Payne 12.9, Russell, 11.5, the latter uncertain) and K, (Payne 5.3, Russell 6.8; the former 

 probably too low). 



Smithsonian Tables 



