When describing stars

PHYSICS · Multi-part · A Level · Physics · Astrophysics · Astrophysics

Problem

When describing stars, apparent brightness is denoted by

b

. (1) State what is meant by apparent brightness,

b

. (2) Show that the apparent brightness

b_{\odot}

of the Sun, of luminosity

L_{\odot}=3.83\times10^{26}\,\text{W}

, is

1.4\times10^3\,\text{W m}^{-2}

when the Sun is

1.5\times10^{11}\,\text{m}

from Earth. State the usual name of this quantity. (3) Calculate the apparent brightness of a star with luminosity

5.0\times10^{28}\,\text{W}

at a distance of four light-years.