M43 (NGC 1982) — De Mairan's Nebula in Orion

Physical characteristics

The nebula glows primarily in hydrogen recombination lines (H-alpha) and other emission lines produced when ultraviolet light from hot stars ionizes surrounding gas. The main source of ionization for M43 is the bright, hot star NU Orionis (HD 37061), whose radiation keeps a local pocket of gas ionized and luminous. A dusty lane or dark band separates M43 from M42, so although they are physically connected parts of the same molecular cloud complex, they can appear as separate objects in visible light.

Names and designations

• Messier: M43
• NGC: NGC 1982
• Other: De Mairan's Nebula

History and classification

M43 has been recorded by astronomers since the 18th century and took its popular name from Jean-Jacques d'Ortous de Mairan. It was later included in Charles Messier's catalogue. Over time, improved spectroscopy and imaging clarified that M43 is part of the Orion Nebula complex and is a site of active photoionization rather than a planetary nebula; this correction appears in many modern sources about nebular classification, including general references to emission nebulae (see emission nebula).

Observation and significance

M43 is accessible to small telescopes and even good binoculars under dark skies as a faint, rounded patch north of M42. Amateur and professional observers study it to learn about star formation, the interaction of young stars with their environment, and the structure of the Orion molecular cloud. Its distance is similar to that of the broader Orion Nebula complex—commonly cited near 1,600 light‑years in many educational sources (distance references)—and it provides a nearby laboratory for understanding H II regions and ionization fronts.

Further reading

For general background on the Orion region and related nebulae, see resources on the constellation Orion and on the larger Orion Nebula complex. More technical discussions of emission processes and young stellar environments can be found in introductory texts on interstellar medium and star formation (emission nebula).