<p>Chapter 21. Problem 58<br /><br />Consider a bright star in our night sky. As

Question

<p>Chapter 21. Problem 58<br /><br />Consider a bright star in our night sky. Assume its distance from Earth is 42.4 light-years (ly) and its power output is 4.00 x10^28 W, about 100 times that of the Sun.<br />(a) Find the intensity of the starlight at the Earth.<br /><br />________________nW/m^2.<br /><br />(b) Find the power of the starlight the Earth intercepts. One light-year is the distance traveled by the light through a vacuum in one year. (The radius of Earth is 6.37 106 m.)<br /><br />_______________MW.</p>

Explanation / Answer

(a) Intensity of star light = 4 * 10^28 / 4 pi ( 42.4*3*10^8*365*86400)^2 = 19.78 nW/m^2 (b) Power intercepted by earth = 19.78 * 10^-9 * pi * (6381060)^2 = 2.53 MW

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