Laurent Mahy

Physical properties of stars such as luminosity, surface temperature, distance, or mass are measured from observations. These physical properties are of paramount importance to understand how stars are born, live, and die in the universe near and far. This chapter discusses the basic concepts used by astronomers to derive key information about stars from the light they emit. We present through a pedagogical approach the methods required for determining stellar brightness (apparent and absolute magnitudes), surface temperature (via black-body radiation and spectral classification), and distance (using parallax and standard candles). We finally review techniques for estimating stellar mass and radius, including the use of binary star systems and stellar evolution models.