What is the Hertzsprung-Russell diagram? Which properties of a star are on the x and y axes?
a) A diagram showing the relationship between a star's age and luminosity; Age on the x-axis and luminosity on the y-axis
b) A diagram showing the relationship between a star's temperature and luminosity; Temperature on the x-axis and luminosity on the y-axis
c) A diagram showing the relationship between a star's mass and size; Mass on the x-axis and size on the y-axis
d) A diagram showing the relationship between a star's color and temperature; Color on the x-axis and temperature on the y-axis