2000AJ....120..382O

The optical appearance of the Orion Nebula is significantly altered by the presence of interstellar extinction. Since Orion is high above the Galactic plane and is nearby, most of this extinction is due to material immediately in front of the associated star cluster. This extinction fundamentally alters the optical appearance of the Orion Nebula. We have quantitatively determined the extinction correction by comparing the surface brightness of the nebula at a resolution of about 1".7 in the radio continuum and the Hα emission line. The results compare well with new determinations made from Hα and Hβ line ratios. Extinction-corrected optical images are generated and discussed. The most important extinction feature, the dark bay that obscures the east side of the nebula, has a mass of about 3 M_☉ and possesses numerous small knots of material in addition to a feature that appears to be a shock. We also find that the thin main emitting layer on the front of the parent Orion molecular cloud is marked by numerous walls and plateaus. Only one such structure had been previously known, the one that produces a bright bar across the southeast portion of the nebula. The sharpest structure is associated with the complex of molecular outflow and infrared sources near the region called Orion-S and is likely to be the result of uncollimated outflow from an imbedded young star.