De Mairan's Nebula (Messier 43 / NGC 1982)
Coordinates, Gaia DR3 distance (398 pc), NU Orionis B0.5 V ionizing star, Fish's Mouth dust lane, and observing guide for M43 in Orion.
Provenance-Backed Scientific Measurements
Every measurement below preserves its unit, uncertainty interval, observational method, reference epoch, quality status, and primary catalog source. See Uncertainty & Provenance for how competing measurements are handled.
| Parameter | Value | Uncertainty | Method & Epoch | Quality Status | Source Archive |
|---|---|---|---|---|---|
| Integrated visual magnitude (V) | 9 mag | ± 0.2 mag | Integrated nebular CCD photometry (excluding V=6.8 NU Ori) | definitive | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
| Heliocentric distance | 1300 ly | ± 35 ly | Gaia DR3 parallax of NU Orionis & Orion Complex members (398 ± 11 pc) (J2016.0) | definitive | ESA Gaia Archive — Data Release 3 |
| Apparent angular dimensions | 20 arcmin | ± 2 arcmin | Optical H-alpha emission comma (20′ × 15′) | high-confidence | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots De Mairan's Nebula (Messier 43 / NGC 1982) at RA 05h 35m 35.00s, Dec -05° 16′ 00.0″ within Orion, alongside peak meridian transit altitudes for 40°N and 30°S observers. Use the RA/Dec Coordinate Converter to compute exact culmination altitude for your latitude.
Astrophysical Context & Structure
De Mairan's Nebula (Messier 43, NGC 1982) is a bright, comma-shaped H II emission and reflection region sitting just 7 arcminutes north of the Trapezium in Orion's Sword, separated from the main body of the Orion Nebula (M42) by the dark foreground dust lane known as the 'Fish's Mouth' ( Sinus Magnus). First documented by French physicist Jean-Jacques Dortous de Mairan in his 1731 treatise on the aurora borealis as a luminous atmosphere surrounding a star, it was given a separate catalog number by Charles Messier on March 4, 1769.
Although physically attached to the same Orion A giant molecular cloud at a distance of ~1,300 light-years (398 ± 11 parsecs), M43 is an independent, self-contained Strömgren sphere roughly 3 light-years across that is ionized not by the Trapezium, but by its own central star: NU Orionis (HD 37061), a young 6.8-magnitude B0.5 V massive triple system.
Because NU Orionis is significantly cooler (~31,000 K) than M42's O7 V powerhouse θ¹ Orionis C (~39,000 K), M43 produces much weaker doubly ionized oxygen ([O III]) emission and a stronger dust-scattered continuum—explaining why M43 responds more strongly to H-beta and broadband UHC filters than to strict O-III narrowband filters.
Practical Visual Observing Guide
- Located immediately north of the dark 'Fish's Mouth' dust bay cutting into the northeastern side of the Orion Nebula (M42), sharing the same eyepiece field at low and medium magnifications.
- Visible in 10×50 binoculars as a fuzzy halo around 6.8-magnitude NU Orionis, just north of the dazzling Huygens core of M42.
- In a 100–200 mm telescope at 80×–140×, M43 curls like a comma or miniatureautilus shell around NU Orionis with a dark interior dust lane curving along its eastern boundary.
Catalog Cross-Identifications & Aliases
Common Aliases: M43 · NGC 1982 · De Mairan's Nebula
| Catalog Authority | Identifier |
|---|---|
| MESSIER | M 43 |
| NGC | NGC 1982 |
| SIMBAD | M 43 |
| WIKIDATA | Q11406 |
Related Objects, Comparisons & Guides
Orion Nebula (Messier 42 / NGC 1976)
Coordinates, VLBI/Gaia distance (412 pc), Trapezium ionizing cluster, and visual observing guide for the Orion Nebula (M42) in Orion.
Flame Nebula (NGC 2024 near Alnitak)
Coordinates, Gaia DR3 distance (415 pc), IRS 2b O8 V hidden ionizer, maple-leaf dust lanes, and observing guide for NGC 2024 in Orion.
Messier 78 (NGC 2068 Reflection Nebula)
Coordinates, Gaia DR3 distance (410 pc), magnitude 8.3, McNeil's Nebula variable outburst, and observing guide for M78 in Orion.
Surface Brightness & Extended Objects Guide
Why surface brightness (mag/arcsec²) governs nebula and galaxy visibility more than integrated magnitude, and how exit pupil controls eyepiece contrast.
Angular Size, Separation & Field of View
How angular diameter (degrees, arcminutes, arcseconds), spherical angular separation, and small-angle physical diameter relate to telescope field of view.
Scientific Sources & Dataset Provenance
- ESA Gaia Archive — Data Release 3 (DR3 (2022-06-13)): Gaia Collaboration, Vallenari, A., et al. 2023, A&A, 674, A1 (Gaia Data Release 3) — European Space Agency / Gaia DPAC
- Revised New General Catalogue and Index Catalogue (RNGC/IC) (2024/2026 edition): Steinicke, W. 2010, Observing and Cataloguing Nebulae and Star Clusters (Cambridge Univ. Press); Verga, M. OpenNGC (CC-BY-SA 4.0 / data tables) — Wolfgang Steinicke / OpenNGC
- SIMBAD Astronomical Database (CDS) (2026-10 release): Wenger, M., et al. 2000, A&AS, 143, 9 (The SIMBAD astronomical database) — Centre de Données astronomiques de Strasbourg