Coalsack Nebula (Caldwell 99 / TGU H1867)
Coordinates, Gaia DR3 3D dust distance (180 pc), visual extinction physics, Emu in the Sky lore, and observing guide for the Coalsack in Crux.
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 |
|---|---|---|---|---|---|
| Mean visual dust extinction (A_V) | 2.5 mag | ± 1 mag | Gaia/2MASS star-count & color-excess mapping (dense cores reach A_V ≈ 15 mag) | high-confidence | ESA Gaia Archive — Data Release 3 |
| Heliocentric distance | 587 ly | ± 35 ly | Gaia DR3 3D reddening jump tomography (180 ± 10 pc) (J2016.0) | definitive | ESA Gaia Archive — Data Release 3 |
| Apparent major axis | 420 arcmin | ± 30 arcmin | Naked-eye dark silhouette (420′ × 300′ / 7° × 5°) | definitive | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Coalsack Nebula (Southern Cross Dark Cloud) at RA 12h 50m 00.00s, Dec -62° 30′ 00.0″ within Crux, 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
The Coalsack Nebula (Caldwell 99) is the single most prominent naked-eye dark nebula in Earth's sky, carving out a pitch-black 7 × 5 degree void immediately adjacent to Acrux and Mimosa in the Southern Cross (Crux). Known for millennia in Indigenous Australian astronomy as the head and beak of the celestial 'Emu in the Sky' (whose dark dust body stretches down through Centaurus, Scorpius, and Sagittarius) and in Andean Inca cosmology as Yutu (the Tinamou partridge), it was first reported to Europeans by Spanish navigator Vicente Yáñez Pinzón in 1499.
Three-dimensional interstellar reddening tomography using ESA's Gaia DR3 catalog shows that the Coalsack is one of the closest molecular cloud complexes to the Solar System, beginning just 587 light-years (180 ± 10 parsecs) away on the southern rim of the Local Bubble and spanning roughly 65 by 50 light-years physically.
Containing ~3,500 solar masses of cold (10–15 K) molecular hydrogen and sub-micron carbon/silicate dust grains, the Coalsack blocks 75% to 99% of visible starlight from the background Carina–Sagittarius spiral arm, though unlike Orion it is completely quiescent and currently devoid of active star formation.
Practical Visual Observing Guide
- Situated at declination −62°30′ immediately east of Acrux (α Crucis) and south of Mimosa (β Crucis) in the Southern Cross, extending into Centaurus and Musca (visible south of ~25°N).
- Best observed with the naked eye or wide-angle 7×50 binoculars under dark southern skies, where it looks like a coal-black hole punched right through the brightest part of the southern Milky Way.
- Place the northern edge of the Coalsack in your binoculars or wide-field telescope to see the dazzling Jewel Box Cluster (NGC 4755) shining like a diamond brooch against the edge of the dark dust cloud.
Catalog Cross-Identifications & Aliases
Common Aliases: Coalsack Nebula · Southern Coalsack · Caldwell 99 · TGU H1867
| Catalog Authority | Identifier |
|---|---|
| SIMBAD | Coalsack |
| WIKIDATA | Q14275 |
Related Objects, Comparisons & Guides
Jewel Box Cluster (NGC 4755 / Kappa Crucis)
Coordinates, Gaia DR3 distance (1.97 kpc), magnitude 4.2, supergiant color contrast in the Herschel 'A' asterism, and observing guide for NGC 4755.
Carina Nebula (NGC 3372 Star-Forming Cloud)
Coordinates, Gaia DR3 distance (2.35 kpc), Keyhole Nebula, Trumpler 14/16 OB clusters, and observing guide for NGC 3372 in Carina.
Horsehead Nebula (Barnard 33 / IC 434)
Coordinates, Gaia DR3 distance (415 pc), Sigma Orionis ionization wall IC 434, and H-beta filter observing guide for the Horsehead Nebula in Orion.
Bortle Dark-Sky Scale & Sky Brightness Guide
Reference guide to the 9-class Bortle Dark-Sky Scale, zenith Sky Quality Meter (SQM) readings in mag/arcsec², naked-eye limiting magnitude, and light pollution.
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.
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
- 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
- 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