effective temperature

The effective temperature of a star is a measure of its total energy output and radius. It is defined by the equation (L = 4\pi R^2\sigma T_{eff}^4), where (L) is the star's luminosity, (R) is its radius, (\sigma) is the Stefan-Boltzmann constant, and (T_{eff}) is the effective temperature. This temperature is a derived quantity, representing the star's equivalent blackbody temperature, and is fundamental to understanding stellar properties.1

Stars are classified based on their surface temperatures, which are estimated from their spectra. The Harvard system, refined over time, orders stars from hottest to coolest as O, B, A, F, G, K, and M. For example, O-type stars can reach 50,000 K, while the Sun (a G-type star) is around 5,800 K, and M-type stars are about 3,000 K. This classification is closely linked to a star's luminosity and its stage of evolution.23