(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

We are asked to calculate the flux at a specific wavelength (f_5500), the surface flux(F) and the radius of a star (Sirius A and then B)

We are given the following:

Brightness of Sirius A: V=-1.47

Effective temperature: 9870K

Central wavelength: 5510 Angstroms

Filter constant: Cv=3.58 x 10^-2 W m^-2 m^-1

We calculated distance earlier to be: 8.14 x 10^16 m

2. Relevant equations

f_5500=Cv x 10^-0.4V

F=((2hc^2)/(lambda)^5)(1/(exp(hc/lambda k T)-1))

3. The attempt at a solution

I calculated the first two parts correctly, getting values of:

f_5500=1.37x10^-1 W/m^2 m

F=1.804x10^14 W/m^2m

I am stuck on how to calculate the radius, as i thought have thought taking a ratio of the two fluxes would work, but i end up with R= d sqrt (f_5500/F)

This gives the wrong answer, the correct answer is found by using the same equation but with the F being (pi F)

I am unsure as to how this equation can be found, and so have no idea how to continue with the question

Any help would be greatly appreciated :D

Thanks

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