Nebulae look dark against the backdrop of stars, but how opaque are they likely to be from inside?
In other words, if our Solar System had drifted into the middle of, say, the Horsehead Nebula, would we be able to see any stars through it, or would their light be blotted out?
Typical Bok globules like the Horsehead Nebula have extinction values of $10 < A_V < 40$ through their centres, as judged from star counts and reddening estimates (Kandori et al. 2005). i.e. Starlight passing through the centre of the clouds is dimmed by 10-40 magnitudes (so by factors of at least $10^{4}$) at visible wavelengths.
If you were at the centre of the nebula, these numbers would only be reduced by just $\sim 0.75$ magnitudes (a factor of two), assuming that by the centre of the cloud, we mean the centre of extinction.
The brightest stars in the sky are around magnitude zero and it would take only 6 magnitudes of extinction to make them invisible to the naked eye. If the surrounding stars were distributed like they are around the Sun, then since Bok globules are only a few light years across, then it is unlikely that even the nearest stars would be visible to an observer at the centre of the globule.
Our eyes are not sensitive to the kind of light that nebulae produce. Once close to them, you cannot see the light they produce. If the Earth was put inside of the nebula you wouldn’t be able to see it.
In some nebulae stars formed inside the cloud illuminate their light through the cloud, making it hardly visible to us.
The Solar System? After gathering the data from our Sun we could calculate the lightness of nearby stars. If we lived inside a nebula, we would notice that the Sun is much brighter. The nebula would be only the dimming light going outside of it.
