Model photosphere
![Some essential steps in model-atmosphere analysis for determining stellar abundances (Figure by Bengt Gustafsson, Astronomical Observatory, Uppsala).](/Images/godic/202501/27/Model_atmospheres_Bengt_Gustafsson1746.jpg")
The photosphere denotes those solar or stellar surface layers from which optical radiation escapes. These stellar outer layers can be modeled by different computer programs. Often, calculated models are used, together with other programs, to calculate synthetic spectra for stars. For example, in varying the assumed abundance of a chemical element, and comparing the synthetic spectra to observed ones, the abundance of that element in that particular star can be determined. As computers have evolved, the complexity of the models has deepened, becoming more realistic in including more physical data and excluding more of the simplifying assumptions. This evolution of the models has also made them applicable to different kinds of stars.