The low-density outer region of a star that is mostly transparent to light. Most stellar atmospheres consist of a photosphere, chromosphere, transition region, and corona analogous to those of the solar atmosphere, although a number of evolved stars, as well as B and A main-sequence stars, do not have transition regions or coronas. Atoms and ions in the photosphere and chromosphere absorb radiation at specific wavelengths, giving rise to dark absorption lines in the stars' spectra, notably the Fraunhofer lines. Absorption lines provide information about the chemical composition, pressure, temperature, rotation, and magnetic field strength in the stars' atmospheres.