Best example is the Coal sack nebula in Crux. distance modulus Defined as m - M. A negative distance modulus means that the object is closer than 10 parsecs to us whilst a positive value means that it is further away than 10 parsecs.
About a third of the Coal Sack Nebula spills over into Musca; most of it is found in neighbouring Crux. There are only a dozen or so (mainly third and fourth magnitude) Bayer stars.
The most famous example in the southern hemisphere is the Coal Sack nebula near α Crux in the Southern Cross.
 See also: Constellation, Constellations, Nebula, Cluster, Delta
  
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