Structure and Physical Conditions in the Huygens Region of the Orion
  Nebula
  HST images, MUSE maps of emission-lines, and an atlas of high velocity
resolution emission-line spectra have been used to establish for the firrst
time correlations of the electron temperature, electron density, radial
velocity, turbulence, and orientation within the main ionization front of the
nebula. From the study of the combined properties of multiple features, it is
established that variations in the radial velocity are primarily caused by the
photo-evaporating ionization front being viewed at different angles. There is a
progressive increase of the electron temperature and density with decreasing
distance from the dominant ionizing star Theta1 Ori C. The product of these
characteristics (NexTe) is the most relevant parameter in modeling a
blister-type nebula like the Huygens Region, where this quantity should vary
with the surface brightness in Halpha. Several lines of evidence indicate that
small-scale structure and turbulence exists down to the level of our resolution
of a few arcseconds. Although photo-evaporative ow must contribute at some
level to the well-known non-thermal broadening of the emission lines,
comparison of quantitative predictions with the observed optical line widths
indicate that it is not the major additive broad- ening component. Derivation
of Te values for H+ from radio+optical and optical-only ionized hydro- gen
emission showed that this temperature is close to that derived from [Nii] and
that the transition from the well-known at extinction curve that applies in the
Huygens Region to a more normal steep extinction curve occurs immediately
outside of the Bright Bar feature of the nebula.
