Are any supergiants translucent? Are any supergiants translucent? Some have volumes thousands of times more than the Sun's while having maybe twenty times the mass of the Sun which makes them sound rather diffuse. If there was a very bright distant star behind the supergiant would we be able to see it?
No mass blob of stellar mass is transparent at any wavelength of interest. Opacities $\kappa_{\nu}$(inverse transparency) as function of wavelength becomes really high and broad band at pressures above &gt; 0.1 bars, for all wavelengths.
This leads to the optical depths $\tau_{\nu}$ being enormous and as transmission is $T=1-\exp(-\tau)$, you won't be able to see through any star, ever.