The theorem, found valid except in rare circumstances, that there is only one internal structure possible for a star of given mass and chemical composition. The calculation of that structure depends on knowing how quantities such as pressure, rate of energy production, and opacity depend on local gas properties such as temperature and chemical composition. The mass–radius and mass–luminosity relations in main sequence stars are among the theorem's consequences. It is named after the German astronomer Heinrich Vogt (1890–1968) and H. N. Russell.
Subjects: Astronomy and Astrophysics.