Star A has a luminosity half that of the Sun (LA = 0.5L ), and star B has a luminosity 4.5 times that of the Sun (LB = 4.5L ). Yet when we observe them from the Earth, we see that they have the same brightness (flux): FA = FB. This must mean that one star is more distant than the other. (a) Which star is farther away? (b) How many times farther is it than the other?
Star A has a luminosity half that of the Sun (LA = 0.5L ), and star B has a luminosity 4.5 times that of the Sun (LB = 4.5L ). Yet when we observe them from the Earth, we see that they have the same brightness (flux): FA = FB. This must mean that one star is more distant than the other.
(a) Which star is farther away?
(b) How many times farther is it than the other?
The luminosity of a star is the amount of light that it emits from its surface. Luminosity and brightness are differentiated from a distance. A highly luminous star may appear less bright owing to its distance from the viewer. The relationship between brightness, luminosity, and distance is :
where,
B =Brightness,
L=Luminosity,
d=distance.
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