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Unformatted text preview: of those spheres. The same total amount of energy must pass through each sphere surface. Since a sphere has a surface area of 4 π × (its radius) 2 , the flux of energy on sphere1 = (the flux of energy on sphere #2) × [(sphere #2's radius)/(sphere #1's radius)] 2 . Notice that the radius for the reference flux (sphere #2) is on the top of the fraction while the radius for the unknown flux (sphere #1) is on the bottomthis is an inverse square law! As the distance INcreases, the flux DEcreases with the square of the distance. See the math review appendix for help on when to multiply and when to divide the distance factor. Put another way: As the flux DEcreases, the star's distance INcreases with the square root of the flux. If you know how much energy pours through the star's surface and you measure how much energy you detect here on the Earth, then you can derive the star's distance from you....
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This note was uploaded on 12/15/2011 for the course AST AST1002 taught by Professor Emilyhoward during the Fall '10 term at Broward College.
 Fall '10
 EmilyHoward
 Astronomy

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