Calculating the distance between the clusters

[CaptCoonoor]

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

 

[phyzguy]

The flux falls off proportional to $\frac{1}{r^2}$. Is this enough of a hint?

 

[CaptCoonoor]

a little bit more please

 

[phyzguy]

Suppose I said the flux from a light bulb 1 meter away is $I_0$ Then I move the light bulb until the flux is $\frac{I_0}{4}$. How far away is the light bulb now?

 

[CaptCoonoor]

Suppose I said the flux from a light bulb 1 meter away is $I_0$ Then I move the light bulb until the flux is $\frac{I_0}{4}$. How far away is the light bulb now?

2 m?

 

[phyzguy]

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?