Explanation:
Why is the
belt of Orion surrounded by a bubble?
Although glowing like an
emission nebula,
the origin of the bubble, known as
Barnard's Loop, is currently unknown.
Progenitor hypotheses include the
winds
from bright Orion stars and the
supernovas
of stars long gone.
Barnard's Loop is too faint to be identified with the unaided eye.
The nebula
was discovered only in 1895 by
E. E. Barnard on long duration film exposures.
Orion's belt is seen as the
three bright stars across the center of the image,
the upper two noticeably blue.
Just to the right of the
lowest star in Orion's belt is a slight indentation in an
emission nebula that, when seen at
higher magnification, resolves into the
Horsehead Nebula.
To the right of the belt stars is the bright, famous, and photogenic
Orion Nebula.
