H-R diagrams: The luminosity of a star is the total amount of energy the star radiates (visible light as well as x rays and all other wavelengths) in 1 second. In practice, astronomers compare the luminosity of a star with that of the sun and speak ofrelative luminosity. Thus a star of relative luminosity 5 is five times as luminous as the sun. One of the most important graphical representations in astronomy is the Hertzsprung-Russell diagram, or H-R diagram, which plots relative luminosity30 versus surface temperature in thousands of kelvins (degrees on the Kelvin scale). shows an H-R diagram. Note that the temperature scale decreases as we read from left to right.
a. What is the surface temperature of a main sequence star that is 10,000 times as luminous as the sun?
b. What is the relative luminosity of the sun?
c. About 90% of all stars, including the sun, lie on or near the main sequence. Approximately what is the surface temperature of the sun?
d. The H-R diagram in Figure 1.49 shows that white dwarfs lie well below the main sequence. Are white dwarfs more or less luminous than main sequence stars of the same surface temperature?
e. If one star is three times as luminous as another, yet they have the same surface temperature, then the brighter star must have three times the surface area of the dimmer star. How would the surface area of a supergiant star with the same
surface temperature as the sun compare with the surface area of the sun?