Hertzsprung-Russell, Mass-Luminosity Relations

Hertzsprung-Russell, Mass-Luminosity Relations, and Binary Stars 

Men can do nothing without the make-believe of a beginning. Even Science, the strict measurer, is obliged to start with a make-believe unit, and must fix on a point in the stars unceasing journey when his sidereal clock shall pretend that time is Nought. 

The veined membrane is nowhere in sight. We can be thankful, at least, for that. 

Bob looks down. The ground is flat. The air is fresh with the faint ozonic smell of rain. Bob is momentarily paralyzed with the shock of suddenly being in a new environment. 

Bob touches the ground beneath his feet to see exactly what he is standing on, but there is nothing unusual about the soil, as far as he can tell. He feels lighter. Gravity seems much lower on this world than on Earth. 

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The Danish astronomer Ejnar Hertzsprung and the American astronomer Henry Norris Russell independently observed a very well defined correlation between the luminosity and surface temperature of stars. That correlation is shown in Figure 12.7 and is called a Hertzsprung-Russell, or H-R, diagram. Most stars, such as our sun, fall in a narrow band on this diagram called the main sequence. Stars in this main sequence have luminosities L that are approximately proportional to 7 s5u3face, or in terms of their mass, M, L °c M3 5. How long a star stays on the main sequence will depend on its mass, which, in ton, is related to the reaction rates in its interior. 

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