Messier 43 (also NGC 1982) is actually a part of the Great Orion Nebula, M 42. It is separated from the main nebula by an impressive, turbulent dark lane.
First reported in 1731 by Jean-Jacques Dortous de Mairan, M 43 is occasionally known as de Mairan's Nebula. Charles Messier included in his drawing of the Orion Nebula, and assigned it the catalog number M 43 in 1769. William Herschel observed it in 1774, and cataloged it in 1783 as H III.1. M 43 shows up on the first photograph of the Orion Nebula, taken in 1882 by Henry Draper.
M 43 is a large bright nebula just north of M 42, appearing 7' north of the Trapezium cluster. Its brightest part is comma-shaped, bordered on the northeast by a dark lane. Faint arcs of nebulosity spread outward from the arc, terminated by the dark lane that separates M 43 from M 42. The dark features along its eastern border are visible in telescopes larger than about 8 inches' aperture. The nebula itself is a fine view even in a 4-inch scope.
M 43 surrounds the young irregular variable NU Orionis (magnitude 6.5-7.6). This star, of spectral type B0.5 V, is apparently responsible for most of the ultraviolet radiation that excites the nebula. NU Ori is quite cool for the central star of an H II region, which accounts for the comparatively low luminosity of M 43 at all wavelengths.
M 43 contains its own, separate small cluster of stars which have formed in this part of the Orion Nebula, and lies at a distance of about 1400 light years.