L’astronomia: un’applicazione della fisica
Newtonian gravitational laws explain the motions of planets around the Sun and the motions of double stars around their center of mass. Small deviations from the predictions of these laws have given confirmation of the general relativity theory. Astrophysics, by means of the analysis of the electromagnetic radiation emitted by the celestial bodies permits us to derive the surface temperature of stars, their surface gravity and their quantitative chemical composition. Motions of the stars as a whole as well as differential motions in their atmospheres can be derived by the Doppler effect on their spectral lines. From the observed data, luminosity, mass and radius, one can derive the internal structure of a star, and therefore the source of its radiant energy. This permits to derive which nuclear reactions occur in the interior, how they modify the structure of the star and determine its evolution. Stellar evolution is the first step for understanding the origin and evolution of the galaxies and of the universe as a whole.