Here L is the luminosity of the star, C is a constant 1, R is the radius of the star in meters, and T is the surface temperature of the star in K°. L = C R 2 T 4 (Total luminosity of a hot sphere) This last fact generates yet another constraint, because the energy radiation of a sphere suspended in a vacuum obeys a law known as the Stefan-Boltzmann Equation: And finally, of course, the total energy generated in the core must equal the total energy radiated at the surface.
It is also the case that the gas pressure at any depth in the star (which also depends on the temperature at that depth) must balance the weight of the gas above it.
In general, the more massive a star is, the brighter and hotter it must be. The dependence on mass comes about because the sheer weight of the star's mass determines its central pressure, which in turn determines its rate of nuclear burning (higher pressure = more collisions = more energy), and the resulting fusion energy is what drives the star's temperature. All stars are about three-quarters hydrogen and one-quarter helium when they are born.) ( Chemical composition also has some effect, but not enough to change the overall picture of what we will be discussing here. They come in a variety of sizes and temperatures, but the great majority can be characterized by just two parameters: their mass and their age. The Hertzsprung-Russell Diagram (aka the Main Sequence)
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