Is Barnard 68 the only cloud so close to us that there are no stars between us and it? Regarding molecular clouds / absorption nebulae / Bok globules / obscuring clouds,

(I'm not sure if there's one generic term encompassing all those and any similar obscuring clouds - I just used "cloud" in the question title),

is Barnard 68 the only one so close to us that there are no stars between us and it?

If not, what is the list of such?  (Are we observationally confident about this, at this stage?)



I guess a related question would be: "about what is the density of bok globules near us?" ... in a cube of 1000pc on a side, about how many bok globules are we talking? One or two or thousands??


http://sci.esa.int/gaia/60207-barnard-68/
Barnard 68 has a surface area of around 10 square arcminutes on the sky and is at an estimated distance of around 160 pc. The volume of space encompassed by a sightline to Barnard 68 is therefore about 1 pc$^{3}$.

The the density of stars in the solar neighbourhood (hydrogen burning stars with mass above about 0.1$M_{\odot}$) is about 0.1 pc$^{-3}$. So it is not surprising that no stars are seen in front of Barnard 68.

At this distance, the brightness of the faintest stars would be around $V \sim 20$ so ought to have been picked up in various observations that have been performed on this cloud. Such stars would be more obvious in the near-infrared, but then you pick up background stars through the cloud and you would need an estimate of the distance.

I'm not actually aware of any clear statement that there are no faint stars in the foreground, though obviously you can't see any in the widely available visible pictures.  

There are lots more Bok globules known which appear to have very little in the way of foreground stars. As I outlined in the calculation above - if they are small and nearby, then that is to be expected. You could also look at the list of "dark nebulae".

Other catalogues include the Lynds catalogue of dark nebulae or the catalogue of southern dark clouds by Hartley et al. (1986).