Heart Nebula (IC 1805 / Sharpless 2-190)
Coordinates, Gaia DR3 distance (2.07 kpc), Melotte 15 O-star cluster, Fishhead Nebula IC 1795, and observing guide for IC 1805 in Cassiopeia.
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) | 6.5 mag | ± 0.2 mag | Integrated Melotte 15 cluster + nebular photometry | high-confidence | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
| Heliocentric distance | 6750 ly | ± 160 ly | Gaia DR3 astrometric parallax of Melotte 15 OB stars (2.07 ± 0.05 kpc) (J2016.0) | definitive | ESA Gaia Archive — Data Release 3 |
| Apparent angular dimensions | 150 arcmin | ± 10 arcmin | Full H-alpha heart shell including IC 1795 (150′ × 150′) | high-confidence | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
| Melotte 15 ionizing cluster age | 0.002 Gyr | ± 0.0005 Gyr | O4 If+ and O5 V main-sequence isochrone fitting (2.0 ± 0.5 Myr) | high-confidence | ESA Gaia Archive — Data Release 3 |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Heart Nebula (IC 1805 / Melotte 15) at RA 02h 32m 42.00s, Dec +61° 27′ 00.0″ within Cassiopeia, 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 Heart Nebula (IC 1805, Sharpless 2-190) is a cavernous 2.5-degree-wide H II star-forming complex located 6,750 light-years (2.07 ± 0.05 kiloparsecs) away in the Perseus Spiral Arm in eastern Cassiopeia, paired immediately alongside its neighbor, the Soul Nebula (IC 1848), across a 300-light-year molecular cloud ridge known as the W3/W4/W5 complex. While Edward Emerson Barnard photographed the vast heart-shaped hydrogen loop in the 1890s, William Herschel had already discovered its brightest northwestern knot in 1787 (now cataloged as NGC 896 / IC 1795, the 'Fishhead Nebula').
Sculpting the 160-light-year central cavity of the Heart is the ~2-million-year-old open cluster Melotte 15 (Collinder 26), which packs nine massive O-type stars and dozens of B-type stars into its core—led by the O4 If+ supergiant HD 15570 (~60 solar masses, 600,000 solar luminosities) and the O5.5((f)) spectroscopic binary HD 15558. Radiation pressure and stellar winds from Melotte 15 have compressed dramatic dust pillars around the core while blowing an open 'Galactic chimney' (the W4 superbubble) high into the Milky Way halo.
Located near the northern edge of IC 1805 is the famous runaway microquasar LS I +61 303, a high-mass X-ray binary consisting of a compact neutron star or black hole in an eccentric 26.5-day orbit around a fast-spinning B0 Ve star, emitting periodic TeV gamma-ray flares.
Practical Visual Observing Guide
- Located 5° east of Epsilon Cassiopeiae (Segin), the easternmost star of the Cassiopeia W, and 4.5° north of the Perseus Double Cluster (NGC 869/884).
- In 10×50 binoculars or a small telescope, the 6.5-magnitude central cluster Melotte 15 is easily spotted as a loose chain of 7th-to-10th magnitude stars.
- For visual observers with a 100–200 mm telescope at 25×–60× and a UHC or O-III filter, the brightest part of the nebula by far is the northwestern 'Fishhead' knot (IC 1795 / NGC 896), which stands out clearly while the huge southern Heart loop requires dark skies and very wide fields.
Catalog Cross-Identifications & Aliases
Common Aliases: IC 1805 · Melotte 15 · Heart Nebula · Sharpless 2-190
| Catalog Authority | Identifier |
|---|---|
| IC | IC 1805 |
| SIMBAD | IC 1805 |
| WIKIDATA | Q488505 |
Related Objects, Comparisons & Guides
Soul Nebula (IC 1848 / Westerhout 5)
Coordinates, Gaia DR3 distance (2.06 kpc), W5 West/East triggered star-formation bubbles, and observing guide for the Soul Nebula in Cassiopeia.
Double Cluster (NGC 869 & NGC 884)
Coordinates, Gaia DR3 distance (2.29 kpc), age 14 Myr, supergiant population, and observing guide for NGC 869 and NGC 884 in Perseus.
Rosette Nebula (NGC 2237 & NGC 2244 Cluster)
Coordinates, Gaia DR3 distance (1.42 kpc), central wind-blown cavity around NGC 2244 O-stars, and observing guide for the Rosette Nebula in Monoceros.
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.
Astronomical Catalogs Explained (M, NGC, Gaia)
How astronomical designations work across the Messier (M), NGC/IC, Bayer/Flamsteed, Henry Draper (HD), Hipparcos (HIP), and Gaia DR3 catalogs.
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