For 10 points, name this measure of brightness from which one can compute a star's apparent magnitude, and which can be measured in lux or lumens.
A function named after this quantity was modeled as a power law with an exponential cut-off by Paul Schechter. Ernst Opik calculated the distance to the Andromeda Galaxy by assuming that the ratio between its mass and this quantity was constant. It is a power function of rotation rate, according to the Tully-Fisher relation. The value of this quantity for which a star's gravitational pressure equals its radiation pressure is known as the Eddington limit. Standard candles have a known value for this quantity, which equals the total amount of energy produced in one second. It is plotted against temperature in a Hertzsprung-Russell diagram. For 10 points, name this measure of brightness from which one can compute a star's apparent magnitude, and which can be measured in lux or lumens.
A function named after this quantity was modeled as a power law with an exponential cut-off by Paul Schechter.
luminosity [prompt on absolute magnitude; do not accept luminance]