barnard68_vlt
Figure 1: Molecular Cloud Barnard 68: A small molecular cloud, or Bok globule, of about 2 solar masses, at a distance of about 500 light-years, and about ½ light-year across, yet not a single star can be seen in it. That means there are no stars between the sun and the cloud. It absorbs all light from the background stars, hence is optically thick. (Illustrated on page 409 of Carroll & Ostlie, 2nd Edition) Credit: FORS Team, 8.2-meter VLT Antu, ESO