Let's say we know the "real" flux of a star in a certain bandwidth because we consider it a black body of known temperature. That's just the integer of the power density, so we find the real flux $F\left[=\right]\frac{\mathrm{W}}{\mathrm{m}^2}$.
How do we find the portion of the flux that reaches us? Let's say $R_{\text{star}}$ is the radius of the star and $D_{\text{star}}$ is the distance of the star from Earth; is the apparent flux then$$
A\left(f\right)~=~ \left(\frac{R_\text{star}}{D_\text{star}}\right)^2 \,F
\,,$$or am I doing something wrong here?
Best Answer
I haven't seen the term 'apparent flux' before. Flux is always 'apparent' in the sense that it depends on the distance from you to the source. Your equation for flux received $A(f) = \frac{FR^2}{D^2}$ is only true if $F$ is the flux at the surface of the star.