Task: Text Categorization
Input (English): Measurements of this quantity are always subject to a Malmquist bias. This property is proportional to the fourth power of the velocity dispersal, and this quantity is calculated using the Faber-Jackson and Tully-Fisher relations for elliptical and spiral galaxies. This quantity is larger for objects with longer periods in systems like (*) Cepheid variables, which have constantly varying values for this quantity. This quantity is known for standard candles. For 10 points, name this quantity that is plotted against temperature in the Hertzsprung Russell diagram, which describes objects' brightness.
Output (English): Science