A vast dark cloud of matter in the constellation of
Orion, and in fact invisibly occupying much of that
constellation. The Cloud, which is about 1,300
light years from Earth, is the largest such
phenomenon known in our Galaxy. Occasionally, local events have rendered some portions of
the dark Cloud visible. For example, the formation of the Trapezium system illuminates a
region commonly known as the Orion Nebula.