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Calculating the distance between the clusters

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  1. Mar 18, 2015 #1
    Blue star 1 is 1.36 parsecs from you, and has a measured flux of 9.6×10−9Wm−2.

    The similar colour star in star cluster 1 has a measured flux of 9.5×10−21Wm−2.

    How far away (in Mega-parsecs) is star cluster 1?

    Can anyone tell me how to start off? I'll do the rest
     
  2. jcsd
  3. Mar 18, 2015 #2

    phyzguy

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    The flux falls off proportional to [itex]\frac{1}{r^2}[/itex]. Is this enough of a hint?
     
  4. Mar 18, 2015 #3
    a little bit more please
     
  5. Mar 18, 2015 #4

    phyzguy

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    Suppose I said the flux from a light bulb 1 meter away is [itex]I_0[/itex] Then I move the light bulb until the flux is [itex]\frac{I_0}{4}[/itex]. How far away is the light bulb now?
     
  6. Mar 18, 2015 #5
    2 m?
     
  7. Mar 18, 2015 #6

    phyzguy

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    OK, good. Now apply this same logic to the stars. By what ratio has the flux decreased? So what is the ratio of the distances?
     
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